Mousetrap Car

I was partnered with Anna Basset to create a car that travels 5 meters when a mousetrap is set off. It was quite a struggle... there was a lot of crying and glue involved. In the end our car came in third place with a time of 7.69 seconds.

There are many factors that went into making the mousetrap car travel the required 5 meters. Based on Newton's first law the mousetrap car would stay at rest unless a force was applied to it, so when the mousetrap was set off the metal bar applied a force that pulled the string that pulled on the axel of the back wheels to cause motion in the wheels. Newton's second law states that force=mass x acceleration which explains how when the car has a small mass and a great force from the metal bar the acceleration of the car is greater. Newton's third law states that every action has an equal and opposite reaction, so when the wheels push the ground backwards the ground pushes the wheels forward causing the mousetrap to move forward.
The disc wheels of our car were lined with balloon rubber causing friction between the ground and the wheels. This enables the wheels to get the most out of the distance so that the wheels wouldn't slide on the ground rather than move forward. Another form of friction is the friction between the axel and the car itself. The less friction between the two the more the axel can move causing more rotations and more distance. If there were more friction between these two the axel would not rotate fast and the car would take more time to go the 5 meter distance.
Anna and I decided to use four wheels in order to keep the car balanced on all sides. We used four discs as our wheels with small axles so that there would be larger RPM. Since the axel was small and there were more rotations, the outer rim of the disc would have to go farther in order to keep up with the rotational velocity of the center of the disc. We also made most of the mass (tape) near the center of the axis of rotation on the wheel so that the wheels would turn faster. If the mass were on the rim, it would slow the car down because the mass is spread out.
The tangential speed is the distance over time which our car moved. The point of winning this project was to have the greatest tangential speed. Our tangential speed was 1.538m/s.
The Conservation of Energy states that energy cannot be created or destroyed; it may be transferred from one form to another, but the total amount of energy never changes. The potential energy, or the energy stored and held in readiness, in the car is found when the lever arm is set back and held with the spring the car and lever arm is not moving but there is energy ready to be used. As soon as the lever arm is let go and begins to move the kinetic energy in the lever arm increases until it reaches the end of its path and stops. The kinetic energy is the energy due to the position of the lever arm. When the car trap is set off the energy from the trap is transferred to the wheels to make the car move. The energy from the wheels is transferred to the ground. Some energy may be transferred into heat from the friction.
The lever arm was a very important part of the car. It allowed us to use more string and increase the amount of distance traveled by increasing the number of rotations of the axle. However it decreased the amount of force, thus decreasing the speed and amount of power created by the car.
The original design of the car had smaller wheels in the front, was lower to the ground, and used many different kinds of materials. Originally the front wheels were bobbins and the back wheels were discs while the axles were needles. After about 28 hours of full on experimenting, glue, testing, remodeling... twice, and crying we finally start from scratch and finished! The original wheels were too small in the front which caused us to make the front wheels even and the clips holding the axles were not strong enough which caused us to change them to hooks. Also, the glue holding the wheels added too much friction to the axle slowing down the car, so we used rolled up tape to secure the discs to the axles. Anna and I constantly changed the lever arm, but in the end we stayed with our original plan of the plastic hanger stick.
We cannot calculate the exact amount of work because the force on car is not parallel to the distance it moves. Also, since the velocity was not constant so we could not find the amount of kinetic and potential energy from the car. We cannot find the force the spring exerted to accelerate the car because you cannot calculate the work. In order to find the force you have to know the amount of work done.
If I were to do this again I would use slightly smaller wheels in the front instead of a drastic size difference or no difference at all. I would also find smaller axles and find a way to use less lever arm so to increase the force and RPMs of the car. This is a video of our car:

Unit 5 Blog

In this unit we talked about work, power, kinetic energy, the Law of Conservation of Energy, potential energy, and machines. I found it most difficult to understand how potential energy and kinetic energy were relative to each other and I think that I could have been more attentive in answering homework questions from the text book. However, I think I did very well in preparing for quizzes.
Work
Work is the force times the distance traveled (work=fd) and is measured in joules(J). In order for work to be done the force and the distance must be parallel to each other, for example when someone picks up a book from the ground work is done on the book. When the person starts to walk with the book there is no work done on the book because the person is walking horizontally and the force of the book is vertical. So if you walk up a staircase that is 6 feet tall (since the distance of the staircase is vertical it is parallel to the force of the book) holding a 20 newton book you would do 120 joules of work. Work=20N x 6ft, so Work=120J.
Power
Power is how quickly work is done (power=work/time) and is measured in watts. Lets say that when you walked up the staircase in the work example it took you three seconds, this means that you would have 40 watts of power. Work=120J and time=3 so, Power=120/3 or Power=40 watts.
Kinetic Energy
Kinetic Energy (KE) is the energy of movement and the ability to do work and is measured in joules. In order to find the KE you multiply 1/2 by the mass and velocity squared (KE=1/2 mv^2). In order to find the change in KE you would subtract the initial KE from the final KE. the change in KE is also equal to work, fd=1/2 mv^2. This also means that if the velocity doubles or triples then the work will either quadruple or be nine times the original amount of work.
Law of Conservation of Energy
 The law of conservation of energy states that energy can not be created or destroyed, it can be transformed from one form into another and is conserved, the total amount of energy never changes.
Potential Energy
Potential energy(PE) is the energy that is stored and held in readiness or the mass times the gravitation pull, or 10, times the height (PE=mgh). An example of potential energy is a rock tittering at the top of a mountain, if the rock weighed 20kg and was 50 ft high then the PE would be 10000 Joules (PE=20x10x50). The PE of this rock is also an example of Gravitation Potential Energy which is PE due to elevated positions. PE only has significance when something changes. The PE at the top of the mountain would be equal to the KE of the rock right before it hits the ground, this is because the PE is transferred into KE due to the law of conservation of energy.
Machines
Machines are meant to make the force you apply in less and the the force applied to an object larger, but the amount of work done will always be the same (work in= work out or f x D= F x d). Machines don't have to be in complicated, for example an inclined plane is a machine. It increases the distance traveled so that the force that you apply to get the object up the inclined plane decreases. This podcast I made in class explains machines.

Machine Photo

In this photo the simple pulley system makes it much easier to pull the american flag up the flag pole. Since the distance of the rope is very large, it takes a very small amount of force to pull the flag up and down the flag pole. So the work you do is equal to a large distance and a small force (work=Df).

Unit 4 Reflection

This unit has been all about centripetal force and rotation. I found it to obtain a lot more information in a shorter amount of time to learn it than most other units this year. I believe that I had most trouble understanding the concept of center of mass, but am now able to understand it due to the review questions my class made. I think that I could have been more thorough when answering homework questions in this unit, that would have helped me understand the center of mass concept as well as the other concepts better and in a shorter amount of time.

Rotational/Tangential Velocity:
Rotational and tangential velocity are two terms determining speeds in rotational object. Rotational velocity is measured in rpm (rotations per minute) and determines the amount of rotations an object has every minute. Tangential velocity is the determined by distance over time an object rotates. If an object such as a carousel is spinning at a certain velocity and one person is near the axis of rotation while his friend is at the edge of the carousel, they would have the same rotational velocity but a different tangential velocity. The boy in the middle would be going slower than the boy on the outside because it takes less time and less distance to revolve around the axis of rotation. The boy on the outside has to have a greater tangential velocity so that he can have the same number of rotations as the boy on the inside of the carol. Another example is two connected gears that can be rotated by a handle connected to one. If these two gears are different sizes but are connected, the tangential velocity of the two will be the same and the rotational velocity will be different. If they have the same tangential velocity then it would take the smaller gear more revolutions to go the same distance as the larger gear.

Rotational Inertia:
Rotational inertia is the property of an object to resist changes in rotation. More mass does cause more inertia, but an objects rotational inertia is dependent on where the mass is located. When the mass of a rotating object is located nearer the axis of rotation, there is less rotational inertia making it easier to spin. When a dancer is turning in forte, she repetitively pulls her arms and leg into her body to spin faster, but then spreads her arms and her leg out to slow down.

Conservation of Rotational Momentum:
The Conservation of Rotational Momentum states that the momentum of a rotating object is determined by the rotational inertia (RI) multiplied b the Rotational velocity (RV) so RI x RV=P. Also, the momentum of a rotating object before is equal to the momentum of the rotating object after, P before= P after. Therefore (RI x RV) before= (RI x RV) after. If there is a large rotational inertia and a small rotational velocity before then there is a large rotational velocity and a small rotational inertia after, RI x rv= RV x ri. This podcast helps to explain what the conservation of momentum is and how it works:

Torque:
Torque is what causes rotation, it is determined by the force(f) x the lever arm(la). When a force is applied to an object farther from the axis of rotation the torque is larger, so the torque is directly proportional to the force and the lever arm of an object. In order for an object to be balanced the clockwise and counterclockwise torque must be equal, so (f x la) clockwise=(f x la) counterclockwise. This also means that is the force is large and the lever arm is small on the clockwise side the the force will be small  and the lever arm will be large on the counter clockwise side, (F x la)clockwise= (f x LA) counterclockwise.

Center of Mass:
The Center of Mass is the center position of all things mass. When the center of mass of an object is above the center of gravity, which is when gravity acts on the center of mass, it is balanced. The taller an object, the taller the center of gravity and the lower the center of mass the more balanced an object is. An example of this is a tight rope walker, he would carry a long drooping stick when on a rope to increase the lever arm and make the force smaller so that he would be more balanced. This can also be applied to a wrester, when they squat down and spread their knees they make their center of mass closer to the ground and create a larger base of support so that they are harder to push over.

Centripetal Force:
Centripetal force is the center seeking force that keeps you going into a curve. This is the only force acting on you, many believe that centrifical force is a center fleeing force that pushes you outwards but this force is fictitious and the reason you move outward is due to Newtons first law which states that an object in motion want to stay in motion and an object at rest wants to stay at rest, so when your car turns right your body wants to continue left. Centripetal force is what keeps a satellite in orbit, however there needs to be just enough initial velocity to get the satellite to continue in orbit otherwise it will crash into the earth or fly out into space.

Centripetal Force

In this photo the bull is rotating around in a circle with me on top. In order for me to stay on the bull, I moved my body to the middle of the bull and tucked my head and elbows into the middle so that my body would be over the center of gravity. This way I would spin with a lower tangential velocity and it would be easier for me to stay on the mechanical bull.

Meterstick Project

In class we were asked to find the mass of a meter stick using a 100g weight. I started by placing the meter stick on the edge of a flat table and put the 100g mass on the very end of the meter stick side that was off the table. I gradually moved the meter stick farther from the table until it became completely balanced with the weight on the end. Then I measured the distance from the mass to the table edge to find the lever arm. The entire meter stick is 100cm so the center of gravity would be at the 50cm mark. I subtracted the distance of the lever arm of the side off the table from the 50cm mark to find the lever arm of the other side of the meter stick. Once I found these components I used the torque equation where the torque of the left side would be equal to the torque of the right side (torque right=torque left). Torque is equal to the lever arm times the force to the final equation would be (Fxla)right=(Fxla)left. I plugged in the 100g mass to the force and the lever arm length off the table on the meter stick and made that equal to the lever arm of the side of the meter stick that was above the table time the variable x. Lastly I solved for x which gave me the mass of the meter stick!

Torque

This video uses illustrations to explain how torque works. Torque is equal to the lever-arm times the force of the rotating object. This video also gives example problems and clearly explains the math involved.