Ten Favorite Things about Physics

One: Inertia

 My favorite concept is Inertia. Inertia is NewtonsTthird Law which states that any object, whether in motion or at rest, will continue doing what it is doing. I thought this was amazing because I thought everything just started at a rest state where there not going and that when we push something we apply energy to the object making it move. I thought that this energy would be used up (in the form of heat) and when it ran out of energy it would stop. But mass doesn't act like a car, instead it's outside forces that do the stopping and starting 

Two: Newton's Second Law of Motion. 

Newtons second Law explicitly states that an object's acceleration is directly proportional to the net force acting on it and indirectly proportional to the mass. I really like this mainly because it was one of the simplest and easiest examples to understand in physics. It makes sense that the more force you put on an object the more it will accelerate (or "decelerate" due to an opposite force). And it also makes sense that the more mass something has the harder it will be to push it. It's much easier to push a small child than a large man. 

Three: Newton's Their Law of Motion 

This concept blows my mind, but makes tons of sense at the same time. Newtons Third Law states that to every action there is an opposite and equal reaction. No wonder I don't just break through a chair when I sit on it, because it pushes back on me (I guess the creaking noise when a large person sits in a chair is the chair actually pushing back).It would also be nice to say that if I hit someone then that person hit me also and the ensuing fight is just as much his fault (though that wouldn't get passed the headmaster). I guess thats why I would have bloody knuckles after the fight, because my opponent was hitting me right back.

Four: Systems 

Another smaller concept that I really like is that a force acting inside of a system doesn't do anything to the system. Only an external force can cause something to move or slow down. A person can't stop him or herself from falling through the air without a parachute and we also need to push on the floor in order to move. 

Five: Tangential vs Rotational 

Tangential velocity is the linear velocity (how fast a spot on a wheel is moving at any point) and rotational velocity is how many rotations a circular object takes. I thought it was especially interesting that a point on the outer part a circle has to move faster (have a higher tangential velocity) In order to keep up with a point closer to the center of a circle. It's just strange thinking one part of an object is moving faster than the other. 

Five: Lever Arm

In a way I always knew, but never realized, that the longer something is the easier it will be to move something else with it. Working with my Dad on projects at home we would always use a longer wrench for more stubborn bolts but I never actually thought about why that made things easier. Because the work formula is W=F times Lever arm the longer lever arm you have the smaller the force if you want to do the same amount of work. "Physics makes good sense" (Paul G. Hewitt).

Six: Centrifugal Force. 

First centrifugal force isn't real, it is merely the name we give to the inertia of us wanting to stay going in one direction while a centripetal force pushes us closer to the center of a circle. I thought that was really cool because I have felt the force of a car pushing against me as I go around a turn. Now when I sit in a car I actually know why my body hits the car door.

Seven: Gravity 

At every moment we are being pulled down towards Earths core and if it wasn't for Newtons Third Law we'd all be screwed and fall straight towards the center of the Earth. This is do to the fact that  every single object (that has mass) attracts other objects. and so we are attracted toward the center of earth. So if a girl says she doesn't find me attractive, i'll know physics says otherwise. 

Eight: Satellite Motion

Thanks to a combination of gravity and inertia we have satellites. If an object is moving fast enough around earth than it will not fall towards earth because it's inertia will keep it going in a linear path, but if it is close enough than gravity will still have an effect causing that linear path to turn and curve around the earth. So in reality satellites (and astronauts) are all in free fall and inertia is the only thing keeping them safe.

Nine: Magnets 

Magnets are amazing. The thought that some invisible force can actually interact and pull or push a force. I thinks it's really cool how magnets repel each other. Because field lines move from north to south (outside the magnet) and south to north inside if you put a south to a south or a north to a north the field lines oppose each other and actually push each other away. But if a North and South are in close proximity their field lines are going in the same direction and so attract. 

Ten: Energy Conservation 

Perhaps one of the simplest but still amazing concepts is that no matter what happens energy is always conserved, Energy in= Energy out. When using electronics or using your very own body you expend energy, but that energy doesn't just disappear it just takes on a different form. Ever touched a computer that's been on for a long time? Feels hot doesn't it, heat is just energy in it's simplest form (think of the sun). Other things such as the noise is also another form of energy. Energy in = energy out, it is always conserved. We can neither create nor destroy energy, just change it's form.

Wind Turbine Reflection

Making a Wind Turbine  

Section 1: Background 

The most basic concept about this lab will be taken from the from our studied of magnetism. We know that as a magnet passes through a coil of ferromagnetic material (like copper or silver) it produces a voltage. But the way voltage is induced is by a change in the magnetic field. The wind turbine provides this change.  

Section 2: Material and Method. 

To create this we needed some pipes in order to create a base. after that we tied some copper wire together in order to create the coils of wire. We used a hollow pipe at the top of the base in order to put a cylinder with batteries on it so that it could spin freely between the coils of wire. This cylinder is attached to the rotor of the turbine so that it spins. We placed four magnets north to south opposite each other so that they could create a changing magnetic filed as the turbine spins them. Inside the base we placed two wires down and had them exit through terminals so that we could complete the circuit for the current to flow.  

Below is a picture of a turbine like my teams.

 

Example of magnets and copper wire used.                                                                                                      

Section 3: Results and Discussion.  

The biggest factor to inducing voltage is making your propellors spin fast, the faster they spin the more change in magnetic field and so more voltage. In order to do this you need big (but lightweight) propellors that also have to be curved slightly so that the wind can push it sideways instead of back. If you use more than one magnet make sure they are far enough apart or else if they are strong enough they may break out of whatever you bound them with and attach together. Also make sure your magnet (or whatever their attached to) can fit into the coils of wire because if they can't, your screwed.

Below is a video our actual turbine working. You can stop it at 0:31.

Unit 7 Reflection

Unit 7 Reflection:  Magnetism

Magnets 

Moving charges produce a magnetic field. A domain is what we call a group of atoms whose electrons are all spinning in the same direction. When all of these domains are aligned is when an object becomes magnetized. Because all of these domains are now aligned they all point in the same direction. This is what creates the north and south poles. The charge always goes north then circles around the magnet into the south side and then up through the magnet to the north side again.  

In the picture above you can see what are called field lines. These are the magnetic charges that go throughout the magnet. As you can see when the north end meets a another north end they actually hit against each other and repel, the same goes for the south end. If you put a north and south pole next to each other the field lines go from the north side to the south side because their domains are facing in the same direction.

Horseshoe and refrigerator magnets are often called permanent magnets because of their lasting magnetic fields. However no magnet is truly a permanently magnetic, just as domains are aligned they can be unaligned. This can happen through a number of ways. Heat causes domains to be unaligned as well as simply hitting a magnet hard enough can jostle the domains. 

 Magnetizing a paperclip 

How can we magnetize a ferromagnetic material that is not magnetic, like a paper clip? First we need a magnet. A paperclips domains are all random, their all pointing in different directions and so cancel each other out. A magnet has a magnetic field because it's domains are aligned. When you bring the paperclip close the domains are attracted by the magnet and become aligned with the magnetic filed. The paperclip now has a north and south pole. The opposite pole of the paperclip is now attracted to the opposite pole of the magnet.

Earths Magnetic field 

Earth is a giant magnet. It has a north and south pole, but the geographic north pole is actually the magnetic south pole. This is why the north side on a magnet is attracted to the north pole. 

Cosmic Rays, Northern lights and Compasses. 

A charged particle moving through a magnetic field will only experience a force if it is moving perpendicular to the field. 

Cosmic Rays:  

 Every day the earth is being bombarded by particles (protons, electrons, photons) called cosmic rays. Due to earths magnetic field these particles are swept up, because they are moving perpendicularly with the field, which causes them to spiral towards the earths poles. 

Northern Lights: 

As the rays that travel along earths filed lines are brought to the poles they interact with the atmosphere creating auroras and other such things.  

Compasses: 

A compass is a tiny magnet allowed to swing around freely on a stick. Because of this it is affected by the earths magnetic field and when it is perpendicular to the field then it experiences a force that pushes it to be parallel with the filed lines and point north and south. 

 

Transformers

A transformer is a device that carries electric charges across empty space. They does by placing two coils of wire next to each other. By giving current (and an magnetic field) to one the other has a voltage induced to it. The coil that has a charge is called the primary, the coil that feels the voltage is called the secondary. It is important to note that voltage is only induce into the other coil only if the magnetic field is changing. This is why DC current will not work on a transformer, because it supplies a steady stream of current. Whereas AC switches back and forth constantly so the field is always changing. In a transformer the amount of coils (or turns) creates more voltage. If the primary has 10 turns and the secondary has 20, then the secondary would have twice as much voltage. This type of transformer is called a stepped up transformer. A transformer that has less secondary turns than the primary is called a stepped down transformer. This is how in a power line the voltage can be stepped up at the power plant and then sent long distances, then stepped down at a site closer to your house. This is similar to laptop chargers who use a step down charger in order to power your computer. Th
e wall socked may have 220 volts but the transformer in the charger pushes the voltage down to around 120 volts.

Equations 

Following these are the equations for the transformers: 

For voltage, turns and to show energy is conserved.

Primary Voltage/ No. of Primary Turns = Secondary Voltage/ No . of Secondary turns 

                                                                             or 

V(p)/Turns(p) = V(s)/ Turns  

Power is conserved equation 

PowerPrimary = PowerSecondary 

Voltage and current 

Primary Voltage X Primary Current = Secondary Voltage X Secondary Current or (VI=VI) 

Coils and Credit Cards 

We now know that when a magnet or a coil move near each other a voltage is induced. Some people found out that this could apply to how we spend money. A credit card has a strip of different magnetic charges along it (this forms the code). The credit card machine has a coil inside of it and as the magnetized strip of the card moves by it, voltage is induced which is then registered by the machine and interpreted as a code.

Motors and Generators 

Because It is much more practical to spin a coil inside a magnet, most people spin the coil to produce voltage. This arrangement of moving a coil in a stable magnetic field is called a generator. A motor is basically the exact opposite of a generator except instead of using mechanical energy to produce electrical energy, it uses electric energy to produce mechanical energy.

        A simple motor/ generator.

A simple generator/ motor.

Electric Currents and Magnetism 

As a wire carries a current, a magnetic field is produced. But if this wire moves through a magnetic field it feels a deflecting force and it will be pushed. If the wire's current changes directions than the force will also reverse. As we know the force is strongest when the current is perpendicular to the magnets. 

Heres the link to a video showing a simple motor: 

https://www.youtube.com/watch?v=O2oDaILnaoM 

How a Motor Works.

Motor Blog 

Parts: 

1. The Battery:  The Battery stores and provides the electric energy for the engine. 
2. Coil of Wire: The coil of wire is meant to carry the current through the motor 
3. Paperclip: Connects the battery to the wire and carries current. 
4. Magnet: THe magnet is responsible for pushing the coil of wire in circles so that it creates energy. 

The Armature 

The ends had to be scraped so that current could flow, but we scraped one fully and the other only partially. We did this so this because if there was a steady flow of current through the wire the coil would not turn all the way around but would turn backwards after one half turn.

Why the Motor turns  

First current flows from the battery up the paperclip into  the coil of wires, back down the other paperclip and back into the battery. The loop itself turned because the magnet field produced by the magnet applies a force up at the coil of wire. The loop had to be vertical so that it the force from the magnet could hit the coil vertically or else there would be no torque. This is do to the right hand rule, the electric current flowing throughout the coil give it a charge. The magnetic field, from the battery, is positioned perpendicularly from the coil and so the force from the magnetic field causes the coil to spin. 

Purpose:

The motor itself has no real practical purpose because its very fragile and doesn't produce a high amount of electricity. However it is a good example  of how a motor works. The only real application it has is to give students an example of electromagnetism. 

Link 

Heres a nice little video of my groups own motor.

Unit 6 Charges and Electricity

Unit 6 Reflection Charges and Electricity 

Equations you should know 

Coulomb's Law 

F=K*q1q2/d^2 

Ohm's law 

V=IR or I =V/R 

Power 

Power = current*voltage 

Voltage = change in PE / q 

Electric field = E = F/q 

UNITS 

F=Force 

V=Voltage 

A=Current 

I=resistance  

q=charge

Charge 

The central theme of this unit is something called charge, which is the imbalance of electrons and protons. Electrons and protons are both charged particles, electrons are negatively charged and protons are positively charged. How an object is charged is when it has two much or to little of either of these particles. An object is neutral when it has an equal amount of electrons and protons. 

Electrons are a little special in this relationship because they are much much smaller than protons. Because their so small (and their on the outside of the atoms nucleus). It is much easier for them to move from one electron to another.  

There are three ways that something can be charged: Contact, Friction and Induction. 

 Contact: When two objects touch and  transfer electrons from one to the other. 

Friction: When two objects rub together and one takes electrons form the other. Visualize taking off a beanie . Do the hairs on your head stand up, If they do than they are being repulsed because they are now positive. The beanie  had stolen some electrons form the hair making both charged. 

 Induction: The process by which an object becomes charged, first by being polarized form a charged object (that is by not touching it) and then touching the object with a a different neutral object allowing the flow of the opposite charges (those not being attracted by the charged object not touching). Now the   original object is no longer neutral and has a charge.

Voltage

One the first things that we learned in this unit was potential difference or voltage. Voltage is the difference between two points of electrically charged areas.  Think of a water pipe, one end has a bunch of water in it the other end has no water, naturally the water will flow from the filed end over to the empty end. This is an excellent example of how Voltage works. The most important thing to know is that Voltage is measued across two points, from the point it flow form to the point it's going to to. We can also say that it is the energy given to each Coulomb of charge. 

The equation of Voltage is change in potential energy over charge. (Potential Energy is the amount of energy a charge could have, it's measured in one point compared to voltages two) 

THe written equation is below: 

V = Change in PE / q 

or 

Volts (V) = Joules/ Coulombs 

Current 

Current is the charge that flows through the circuit from point a to point b. It's what Voltage pushes along. 

Current is measured in Amps. 

It's equation is Amps (A) = Coulombs/second 

or 

A = q/seconds  

current flows through the electrons in a circuit form one place to another. So if voltage is turned off  there is no current flowing.

AC/DC 

There are two different types of current. AC (Alternating Current) and DC( Direct Current). As the names imply AC is current that alternates meaning that it switches directions. flowing on way along the wire and then the opposite way a moment later. DC current is (as it's name implies) direct meaning that it doesn't change direction and keep going the same way. 

Resistance

This is what resist the flow of charge. Certain properties of a circuit will effect how easily a charge moves through it. The wider the wire the less resistance because the the electrons that flow though the wire constantly bump along the sides. The wider the side the farther they will go in without hitting a wall. Heat is another factor, the more heat you have the faster the electrons move. If you tried going through a room that had a bunch of people moving very quickly it would be pretty hard to get to the other side. So the higher the heat the higher the resistance. Also the longer the wire the more resistance the electrons will encounter because they will have a much longer way to go. 

The units for resistance are Ohm's 

Ohm's Law 

Ohm's law states that current that passes through a conductor is directly proportional to the potential energy.  

I =V/R 

or 

V= IR 

V = Voltage 

I = Current 

R = Resistance 

The Speed of Light 

Do electrons really move the speed of light? No. Electrons move excruciatingly slow, instead it is the Energy/electric field that moves so quickly. Energy merely passes through the electrons ( and nudges them a little bit) so that it can get form point A to point B. 

 The electric company pumps something into your house to make your appliances run. What is pumped into you house? Electricity! But what about the electrons, there already in the wires, there in the stoves, lightbulbs, toasters, dishwasher, act. THey are always there in fact they help make up those things. Their all cluster around other clusters of Protons in a huge atom sea. Even if you touch a power line the electrons don;t move very much (only a little bit) but it's the energy that hurts you and that passes through you. 

Coulomb's Law 

How do changes in distance affect force? 

Coulomb's Law or the inverse square law tells us that the closer the charge the stronger the force.  

The mathematical formula of this is written below. 

F = K*q1q2/d^2  

An excellent example this is the ballon problem described above (in friction). You you rubbed the hair with the ballon and it stole some electrons the ballon then became negatively charged. If you were to put that negatively charged ballon next to a wall it would do something called polarization where the negative charge of the balloon pushes the negative charges of the wall away but pulls the positive charges closer. The wall's net charge is still zero the charges are simply seperated. Now the negative charges are much closer to the positive charges and so have a stronger attracting force than the farther away and repulsive negative forces.

 

Coulomb's law is also called the inverse square law because distance and force are inversely proportional to each other. 

2d=1/4F 

1/2d=4F

Electric Shielding 

If you have say an Xbox and you want to keep it running well, then you will want to keep that metal box around it, because it serves a special purpose other than to just look good. THere is this thing that is called an electric field, everything from cars to VCR's have an electric shield. THis thing is a conductor that stops charges from entering a certain area and damaging the delicate things inside (I.e. humans, circuitry). It does this by distributing the charge equally over the conductor. If a charge is the same (positive on positive, negative on negative) then they would naturally repulse each other. So the positive or negative charge will push themselves away from each other and around the conductor. Now the charges are pulling on every single part of the inside of the conductor, which means that even if the inside is oppositely charged than the outside. The inside is still neutral. Even if you have a negative charge closer to one wall then the other. Due to Coulomb's law the outside charges closer to that inside charge pull harder than the charges on the opposite side. But there are more charges pulling the negative on the opposite side, so neutrality is conserved. 

The equation for electrical shielding difference is E=F/q

Power 

Power is the rate by which something does work. 

It's formula is Power = VI 

The units of Power are joules per second or the watt

Parallel and Series 

There are two types of circuits along current can flow, Parallel and series circuits. 

Series is the more simpler of the two. It's just a simple circuit with one or two light bulbs attached in side by side. Because of this current has only one pathway that it can pass through. The resistance of these bulbs is the sum of each individual bulb.Voltage is also evenly distributed amongst the bulbs so that if you add them up they would equal the voltage of the source. 

Each bulb                        Total 

V=12v                            V=IR

                                          =3(2)

                                          = 6v 

                                        

R= 2 +2                          R=2 ohm's 

  =4 

I = V/R                            I=I

  = 12/4                             =6v

  =3A  

Parallel circuits are when you take two or more bulbs and attach them so that each bulb has it's own pathway to the battery. This makes it so that if one bulb blows the other can still run because it will have it's own own full circuit to the battery. The total resistance in a parallel circuit is half the resistance of one of the bulbs. Voltage remains the same always (this is why it glows brighter than series). And the current of a bulb adds up to the total. 

the following is true about parallel circuits

Each bulb                          Total

R= 2ohm's                         R= 1/2 (2) =1 ohm.                                             

I = V/R                              I = V/R 

 = 12/2                                 = 12/1

  = 6A                                  = 12A

 

V= 12v                               V=12v

Fuse 

A fuse is a small device that is inserted on a circuit so that it can stop the flow of current if it gets to high. When the fuse gets to hot it will melt and stop the flow of current.

What I liked 

I really liked this unit because it was interesting to find out how electricity actually powers the things that we own. Like other physics units it's really applicable to everyday life and it's interesting to think about. 

What I would do better next time. 

I'm goeing to try and pay attention a lot more during labs, I often feel like I don't get very much done or I just don't know whats going on and so i'm left feeling confused.  

 

Ohm's Law resource

Here's a great resource for Ohm's law.I think it really helped me understand how voltage relates to Ohms law and also gives some good examples to make things clearer.

I thought this was great introduction video into voltage. It focuses a lot more on current than I feel we do, but it also gave some great analogies by using lakes and rivers that would be great for any beginner physicist.

Mousetrap Car Reflection

Mouse Trap Car Reflection 

Speed: 8.64 Sec 

Place: 8th (last) 

Picture 

 

Part A, the wheels: These were made out of vinyls. We made these so big because we needed something to keep the base from touching the ground.

Part B, nuts and washers: My brother and I used nuts and washers that were tight enough to not move on the wooden rod so that the wheels could stay in place.

Part C, the string: We used a small pink string to attach the wheels to the mouse trap. This was the part of the car that pulled on the axil so that the car could move.

Part D, The weight: In order to keep the base from moving we needed some form of weight in order to keep it in place.

Part E, The base: This consisted of a block of pine wood with a mouse trap glued to the top. This allowed the mouse trap to go off and pull the string so that the the axil could move.


Reflection: 

Question a. 

Explain how Newtons first, second and third laws apply to the performance of the car. 

Newtons First Law states: That any object will want to keep doing what it is currently doing and will only stop or start if there is an outside force. (Law of Inertia) 

Newtons second Law states: The acceleration of an object is  directly proportional to the force of an object and inversely proportional to the mass 

a = Fnet/m 

Fnet = a times m. 

Newtons third law states: When an object exerts a force on another object, that second object exerts an equal and opposite force on the first object. 

We knew that our car was going to be very heavy and so the force apply on the cart just to make it move would take most of the mouse traps energy. We were guessing that once the mouse trap had done it's job the car would have been going fast enough that Inertia would carry it's way through what was left of the 5m. We were right because it went another 1-2 meters after the line.  

The acceleration of our car was very slow at first (for a second I was scared it wasn't going to move) but after a few moments the car started to pick up speed. The reason our car moved so slowly was because the ratio of Force to Mass was very disproportionate. The force was much smaller than the mass of the car, making the acceleration smaller.  For example say the mouse trap applied a foirce of 5N on a car that had a mass of 20 grams.  

a = Fnet/M 

a = 5/20 

a = 0.25 m/s^2

That is a very small acceleration, which explains why our car went so slow. 

 It was interesting to notice at the beginning of the race how slow the the mouse trap actually moved in comparison to how it would move when not attached to an axel. As the mouse trap started off it had to apply a force in order to get the car to move. Because of Newtons third law the Car would push back on the mouse trap, but we had attached the trap to the axil which may the force.

The mouse trap exerted a force on the axel of the car and in turn the axel exerted a force on the mouse trap. Due to the circle shape of the axel the two opposing forces pushed the axel in a circular motion which in turn turned the wheels. If the Mousetrap was the only one applying force then in would simply be pushing the car backwards instead of moving the axel.

  

Question b.  

What are the two types of friction present? What problems related to friction did you encounter and how did you solve them? How did you use friction to your advantage? 

Friction is a force that to stop an object from moving

There are two types of friction going on in the car, static and kinetic.
 Static friction is a force between two non moving objects while kinetic friction is between something that is moving.

Static friction wasn't a big variable in the creation of the car, but kinetic was because it directly opposed the movement of our car. My brother and I offset the the effects of friction by choosing only two very thin wheels so that there was less surface contact and so less friction.

We used friction to our advantage in order to help keep parts of the car in place. The wheels were originally held only by nuts and bolts. we got tight enough bolts to make them stick on the two wheels in order to hold them in place. We also hoped that the force of friction would hold the nuts together. It was largely successful as the wheel did stay in place, but then we glued the nuts the wheel so that it wouldn't wobble as much.

Question c.

What factors did you take into account to decide the number of wheels? What kind of wheels did you use in each axle? What is the effect of using large or small wheels?

We chose to go with two wheels knowing so that there would be less friction acting against them. The types of wheels we chose were vinyl records and so there was no need to attach balloons on the end without making the wheels to big. Unfortunately the wheels had to be big in order to hold up the axil. This would make it harder for the Mousetrap to move the car because of the bigger diameter and mass. The wheels would also have to move at a faster tangential velocity in order to match the rotational velocity of smaller cars.


Question d. 

As the mousetrap is pulled back it gains potential energy and has it's max whenever it is pulled all the way to the back of the block of wood. As the trap is released that PE is changed into Kinetic Energy. The closer the trap gets to the other side of the wood the more Ke it has so that when it hits the other side of the block it has release the maximum amount of energy and the car should be moving it's fastest. This would explain why our car went so slowly at first but then picked up speed as the trap neared the other end.

The energy of the system was conserved. As my brother pulled back the trap he put energy into the trap  and when it was released the potential energy was transferred into the axis which made the wheels move and the rest of the energy was released as sound, heat, and friction.

Question e.

Our lever arm was only the length of the trap itself so there was much less work being done on the car. So the pulling force was much smaller than other cars who lengthened there cars lever arms substantially, this is one of the reasons why our car didn't go very fast. The power output was very small so our car did not go fast at all. Creating  a longer lever arm for our car may not have worked because it would just hit the ground.

Question f.

Rotational inertia played a big role in the function our car. We knew it wouldn't very much force and because the lever arm wasn't very long it's force alone would carry us through the finish line so we relied a good bit on the inertia of the wheels to get us 5 meters.

The car had to also move at a faster tangential velocity so that it could match the much higher rotational velocity of other cars. Unfortunately due to the small amount of work exerted by the mouse trap and the size the mass and the wheels our car trap could not exert enough force to move the wheel very quickly.

Question g. 

Why can't we calculate the amount of work the spring does on the car? Why can't we calculate the amount of potential energy that was stored in the spring and the amount of Kinetic energy the car used? Why can't we calculate the force the spring exerted on the car to accelerate it?

We can't calculate any of this because the direction of the force being applied is always changing. The trap is moving in a circle, the axel is moving in a circle, even the spring releases the energy was coiled into a tight circle. There is work being done it's just when the force and distance are parallel, it changes to quickly to another velocity. The KE  and force would also be impossible to find because KE = mv^2 and force = m times a (acceleration is the rate of change in velocity) in order to do that we would need to find the velocity, but since it constantly changes direction we can't put it into the equation. 

Reflection 

a. How did your final design compare to your original design? What prompted the changes?

We only had one design. Besides some small changes such as changing from fishing wire to string and gluing the wheel son we had basically the same design. Although we did attach a weight to the bottom in order to keep the base from spinning.

b. Discuss the major problems encountered in the performance of your car and what you did to solve them.

Our biggest problem was making sure the base didn't move, so we just attached a weight to the bottom and it stayed there. But we also wanted to make sure the car would make it past eh line so we bought the lithest materials we could and got thin wheels to decrease friction.

c.

I would try to make the wheels smaller and the lever arm much longer, perhaps even attach two lever arms to the trap and two strings to see if that adds any work. I would opt for more wheels in order to have a longer lever arm so the car could go faster.



Heres the video for the mouse trap car.

UnIt 5 Blog reflection

UNIT 5 

Over the course of this unit we have studied machines, work and power.

Work 

Lets say I'm walking up some stairs and I start to wonder, wow there must be some kind of physics going on that allows me to walk up these stairs. Well there is, it's called work.

Work is the amount of force that you apply over a certain distance, or in equation form:

work = force times distance.

As I start climbing up those stairs I apply a certain amount of force over a certain amount of time that allows me to get up those stairs.

Lets say that I weigh 600N and I want to get to the top of a flight of stairs 4 meters tall. How much work will I do?
 since work = f times d all we need to do is start plugging in numbers, so:

600N times 4 equals 2400 Joules.

It took us 2400 J's to get to the top of the stairs. Wait, what in the world are Joules? A Joule is equal to the amount done by using the force of one Newton over the distance of one meter. But all you really need to know is that it is used as the unit of measurement for work.


Now lets say you go out to a nice restaurant to eat and you ( being a smart physics student) notices that the waiter is applying a certain amount of force on his food tray, while he is walking a certain distance to deliver the food. And you say that some work is being, thats actually not true. Because in order for there to be any work done force and distance must be parallel. the force that the waiter used to pick up the tray needed some work, but the act of walking did not.


Power 

Now theres this other thing called power, which is how quickly work is done.

The equation for power  is  Power = work over time


Which is pretty simple, if you push a box for 10 seconds while doing a total work on it of 100 J than you would have a total of 10 watts of power. Notice that the measurement for  power is watts, which is the same as a lightbulb. a lightbulb is a great example of power, Say you have 60 watt light bulb, that means that the lightbulb uses 600 J of work every 10 seconds.

Work and Kinetic Energy 

 So lets say we're driving a car at 10m/s like safe Asheville school students, but all of a sudden a little boy jumps into the road and we skid for 3m to a stop and let the child pass. Now we're in a different lane and going 20m/s when all of a sudden an overpass breaks down 10m in front of us and we immediately press on the breaks. Will we stop in time or will we rash into the broken down over pass?

Notice that we have two velocities and a distance. But how are we going to find the distance it took to stop? We could use the work formula because it has a distance, although we don't have a force. But don't worry physics has an answer, it's called the energy of movement or Kinetic Energy and lucky for us it is equal to work.

Like most things in physics KE has a formula, which is: KE = 1/2mv^2

Now how do we know we're going to survive, well we know that 20m/s is two times greater than 10m/s so we must have skid to a halt in 6m. Unfortunately, no.

According to the formula for KE (1/2mv^2) the velocity is squared, making us go four times as far. 4 times 3 equals 12. Lets hope we survive the crash.

Just to prove it to you i'll even work out the equation for you:

KE = 1/2m (2v)^2
      =  4(1/2mv^2)

Work = KE

4(work) = F time 4(distance)

Distance equals 12 meters.


Machines

Heres another basic physics principle for you, it's called a machine.

Lets say you are moving houses  and have rented a Uhaul truck, But the box is to darn heavy for you to carry. Lucky for us Uhaul provides a free ramp with the truck and all you need to do is push the box up the ramp and into the truck.

 How in the world does that make things easier? Aren't you still pushing the box up the same height? Yes the box is being push up the exact same height, but theres something a little different. Remember the formula for work, W = F times D, well when you push that box up the ramp or are able to lift it up you exert some work. It was to hard for you to carry up because you couldn't apply enough force, but when you push it up a ramp the distance was increased enough so that a smaller amount of force could be used to push it onto the truck.

But lets say you got a stronger friend of yours and she was able to lift it up without a ramp, she exerted more force over a shorter distance in order to bring that box up.

This is where we get our formula for Machines, Work in = Work out.
                                       
You used a longer ramp and less force while you'r friend used more force and less distance, but you both still lifted a box into the same truck bed. So both of your forces are equal. You simply used a longer distance in order to make things easier.

In formula form it would look like this:

Work in = work out

F times D = F times D 

Therefore, machines like the one above are used to decrease the force needed by increasing the distance needed.

Potential and Kinetic Energy:

If Kinetic Energy is the energy of movement, what is going on when an object has no velocity? Is there any energy in it at all. There is this thing called Potential Energy, which is the energy that an object at rest has the potential to have.

Lets say there is a large rock sitting precariously on the edge of a cliff that weighs 1000J, this means that the rock has a total PE of 1000J, if for some reason a strong gust of wind came along and pushed that rock off the cliff it would immediately start converting PE into KE to the point where right before the rock hit the ground KE would equal 1000J. Because change in KE = change in PE the more KE we have the less PE we have.

As soon as that rock settled itself on the ground the PE would be 1000J again, right? Well not according to the formula for PE, Which is PE = mgh. The h in the formula represents height and if the rock is settled on the ground then it has no height and so PE = zero.



Conservation Of Energy: 

Have you ever been on a roller coaster? Well I haven't, but I do have a small insight on how it works thanks to physics. Lets say you're sitting on the top of a roller coaster  with approximately 1000J of PE. As you roll down and reach the bottom of the area in between the other hill your PE equals zero and your KE equals 1000J! But as soon as you crest that hill, lets say you now have 300J of PE but still have 700J of KE left over so that you easily make it over the hill. Once again you fall down into the dip between hill, PE equals 0 and KE equals 1000J. Then cresting a larger hill than the last you have 600 J of PE and 400J of KE. Notice that all of these values equal up to 1000, which was the starting amount of Joules. Energy is conserved on a roller coaster and the cart can continue moving (excluding outside forces such as air and friction) as long as the very first hill is longer than all the other hills.

In case you didn't understand how the conservation of energy works, heres my units podcast:



Important connections: 

Because it's imperative that we know how things connect together i've compiled some of the formulas of this section and shown you how they relate

Work = Force times Distance

Power = Work over time

PE= mgh

KE= 1/2mv^2

change in KE = change in PE

change in KE = work

change in PE = work

change in KE = KE initial - KE final

Efficiency = Work out/ work in

Work in = Work out



Review:

For some reason this unit has been a little difficult for me. I thinks it's mostly because i haven't been completing my homework (I did complete all my homework) but I just didn't check over it again to make sure I got them right. I really think this impaired on my last two quizzes, which when I looked back over they were fairly simple. I think next unit i'm really going to pay attention to what I missed on homework assignments, instead of day dreaming in class.

I liked this unit because it explained a lot about how objects move and why they move. It was really interesting to learn that work, force and energy are not all the same thing, but entirely diffe
rent concepts on there own, although they are related to each other

Work and Power resource

This is a great resource because it gives all the definitions that Ms. Lawrence gave us plus a little bit on energy. It doesn't provide as many real life examples as our classes but when it does it uses the same examples Ms. Lawrence used. It goes a little quickly, but other than that it's a good video.

Unit 3 review

Unit 3 review. 

What we discussed in this unit was centered around the concept of Torque. 

What is Torque? 

Torque is combination of force and the lever arm applying that force that causes rotation.

The equation for Torque is Torque = (Force)(Lever arm) 

The units used for torque are NM (Newtons meters) 

The lever arm is the distance from the object that is being pushed upon. 

An example of Torque is when someone tries to turn a bolt with a wrench. If that person can't get the bolt loose he could either find someone stronger to apply more force or get a bigger wrench to increase the lever arm, or he could do a combination of both. 

  

Another Concept we explored was the center of mass/ gravity. 

The center of mass is the mean position of all an objects mass where gravity is principally acting upon. 

 If the center of is inside an area called the base of support then the object with not fall ( due to gravity)

THe base of support is the area where the most of the weight of a body is supported by

Is these two dominos the red circles are there centers of mass. the first one is safely positioned above the base of support (the red arrows point to it). The second one has is CM outside of the base of support and so is producing a Torque. 

Why do athletes widen there feet ?

 This increases their base of support so it's harder for them to get knocked down. 

How do Ice skaters move faster when they bring there arms in

                                          

Why do Ice skaters spin faster when they bring in there arms? 

This is due to a concept called rotational inertia, which means that once an object remains rotating it will want to keep rotating (like the Earth!). The farther away an objects mass is from the center of gravity the harder it will to make it move. As the ice skater brings in his arms he brings all his mass closer to his center of gravity, thus making him go faster. 

Angular momentum is the momentum at which the skater is rotating. Two things create determine the position of angular momentum. 

1. Rotational Inertia 

2. Rotational Velocity 

So the equation will look like this 

Angular Momentum = Rotational inertia times Rotational Velocity 

And because momentum is conserved  angular momentum before = angular momentum after 

 which could also be displayed as. 

Rotational inertia times rotational velocity = Rotational inertia times rotational velocity.

Now lets complicate things by adding Torque and the Center of Mass into one problem

The meter stick pictured above is on it's center of mass (where the fulcrum is positioned). Lets say that one side of the the stick has a heavier weight attached to it. how are we going to make the meter stick balanced again. Now the fulcrum has split both sides of the meter stick into two halves. Both sides could cause a torque depending on which one is bigger. But in order the the stick to be balanced the counter clockwise torque must equal the clockwise torque. In an equation it would look like  torque = force times lever arm equals torque = force times lever arm. So if one side of the meter stick has a bigger weight (i.e. force) then the other side would need to have a longer lever arm for the meter stick to be balanced.

Now lets take a look at rotation.  

There are two velocities that act on rotating object.

Tangential velocity is the first. T velocity concerns the speed of a rotating object like how fast it is moving. 

If we take a look at the picture above we can see that the figures are actually moving faster the farther they get away from the center of the circle and that the center figure is merely rotating. Why is this? lets take a look at the other type of velocity to answer that question. 

Rotational Velocity is how many times an object circles back to the point at which is started rotating.  

If we take a look at the two gears above we can see that one is larger than the other. The smaller one has a larger rotational velocity because it takes less time to circle around to it's starting position while the big one has a smaller rotational velocity because it takes longer to circle around to the same point at which it started at. 

Of course if the bigger gear wanted to keep rotating at the same speed as the smaller one it would need to increase it's speed (or it's Tangential velocity) so that it could rotate more.  

While we're on the topic of rotating lets talk about the concept of centripetal force

Centripetal force is center seeking force that causes an object to turn. 

As seen in the picture above the centripetal force is represented by the center blue arrow, this force is what causes something like a car to turn in another direction. The green arrow represents the cars  velocity as it attempts to keep going the same direction. Although if neither of the forces are stronger than each other than the car will turn in between both arrows in the direction of the black arrow. 

Have you ever been sitting in a car while it's turning and felt like you ran into the side door. Well that due to something that we call centrifugal force. Though this is not a force at all is is merely the product you going forward while some centripetal force is being applied and you wanting to stay forward. that car door is actually pushing on you causing you to turn.

Centrifugal force is also the reason why clothes get dry in the drying machine. The cylinder that your clothes are put into hold then in but because there are hole in it some water is not forced to stay in while the machine is spinning. So the water simply keeps going in the same direction right through those holes and out of your clothes.

What was difficult. 

THe ONQ's were really hard. I often missed little details or even large concepts that cost me points. I did much better on the regular quizzes because I understood what I got wrong on the ONQ's. I haven't really overcome this but my regular quiz scores have jumped since last semester. I'll try to take better notes ( i.e. make them clearer) so that I could do better on the ope note quizzes. I'll also try to pay attention to more of the details in the videos.

Real World Problem.

What if I took a fan and used it to blow over a cup sitting on a table. Now if I move that fan farther back it would be harder to blow over the cup, but when I moved the fan away from the cup am I not increasing the lever arm? Wouldn't it be easier for me to knock the cup down?

FInd the mass of a meter stick without a scale

In this lab my partner and i were trying to find out how we could find the weight of a meter stick without using a scale. We did this by performing the following experiment.



Part 1 Demo:

A. The stick was not balanced and has a torque because the lever arm and the force are to big on one side of the measuring stick.




B. The stick is now balanced, the same amount of force is being applied to both side of the meter stick, Both sides of the stick have the same length of lever arm and it is balancing on the Center of Mass.




C. When we add a weight to one end of the meter stick we have to move it so that the end with the weight has a shorter lever arm then the arm with no weight so it can be balanced.




Part 2 Planning:

These are the equations we will use for the experiment


Counterclockwise Torque= Clockwise torque

Force times Lever arm= Force times Lever arm (to find the force)
The force of gravity equals 9.8 (to find the weight)

w=mg ( to find the mass)


Part 3 the Experiment:

Counter clockwise torque = clockwise torque
Force times lever arm = Force times lever arm

.2 is the distance from fulcrum to weight.
.3 is distance from fulcrum to the center of mass.

.3 = (.98) (.2)

.3f/.3 = .196/.3

w =. 65


w=mg

.65= m (9.8)

.65 / 9.8 = m
.066 Kg


Part 4 Picture:
Follow this link and it will bring you to an example of the lab I just explained.


http://prezi.com/idgqzcbbbnd9/?utm_campaign=share&utm_medium=copy

Torque and Center of Mass

These two videos are form my math teacher's favorite website: Khan Academy. There great for explaining in detail the concepts of torque and center of mass.

Rotational inertia and Angular momentum

Heres a good resource that I found on youtube. I thought it gave clear explanations and examples of what rotational inertia and angular momentum are.