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.