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.