Mousetrap Car
My partner was Holt Mettee, and we worked very well together. The process was long, tedious, and frustrating but in the end we figured out how to correctly apply our physics concepts to the car. All our hard work paid off in the end, because we won our class race!Our car went....
velocity = distance
time
= 5
2.91
=1.718 m/s
This time put us in 1st place for our class as well as out of all the classes!
This is our car!!
 |
Next we glued on our wheels. We put rubber bands around them to create a small amount of friction between them and the ground, thus giving the wheels something to grab onto.
Newton's 3rd law --> car pushes ground back, ground pushes car forward. This is the force that is doing work on the car, and causing it to accelerate.
The tricky part was making sure that they were straight, and parallel to each other.
We added styrofoam on either side of the wheels to keep the wheel steady while rolling. This insured that the wheel wouldn't wobble while rolling, thus that it wouldn't move in one direction more than another.
We added some electrical tape in between the wheels and the axis slot to insure more that the wheels wouldn't slide towards one direction more than another.
This is the axis. The axis goes through the metal holes, having little friction, allowing it to rotate. The wheels are glued onto the axis, so when the axis rotates it allows the wheels to rotate as well, while keeping them straight and parallel.
The next part was to add a lever arm. A common misconception is that the lever arm increases the force, thus creating the car to go faster. In fact, the lever arm is increasing the distance and decreasing the force. The longer distance allows the force to act on the car for a longer period of time.
1) How Newton's Laws apply to the Mousetrap car and how it works
Newton's 1st law states, "An object in motion will stay in motion and an object at rest will stay at rest, unless acted upon by an outside force."
--> A car in motion will continue in motion unless a force pushes it backward (friction)
*Remember that we only like friction in this experiment when there is a little bit on the wheels. Everywhere else, friction is your enemy.
Newton's 2nd Law states, (a = F/m)
--> Acceleration = force/mass
*big force = big acceleration
*too much mass = little acceleration
*We want a small amount of mass with a big force.
Newton's 3rd Law states, "Every action has an equal and opposite reaction."
--> Car pushes ground back, ground pushes car forward. This is the force that is doing work on the car and causing it to accelerate.
2) Our wheels relied on friction due to Newton's 3rd law. We put rubber bands around them to create a small amount of friction between them and the ground, thus giving the wheels something to grab onto.
rough surface = more friction
smooth surface = less friction
... so we had to find the right balance between rough and smooth.
*On the wheels was the only place that friction was our friend.
3) In terms of wheels, Holt and I changed our wheels at least 100 times, because we needed to find the right balance for wheel size, so that we could cause a torque on the wheels. The body shouldn't have a torque, but the wheels need a torque to turn. The force of friction on the ground is what causes a torque.
Bigger wheels = longer lever arm, but too much rotational inertia
Smaller wheels = not a long enough lever arm, and not enough rotational inertia.
Medium size wheels = a good size lever arm and the right amount of rotational inertia.
4) The Law of Conservation of Energy states, "the total amount of energy in a system remains constant (is conserved), although energy within the system can be changed from one form to another or transferred from one object to another. Energy cannot be created or destroyed, but it can be transformed."
--> When the mousetrap is pulled back, there is potential energy built up before the trap is released. When the trap is released, the energy become kinetic energy, because kinetic energy is the energy of movement.
5) Rotational velocity - the amount of rotation that a spinning object undergoes per unit time. The wheels have a rotational velocity.
Big wheels = large rotational velocity
Small wheels = small rotational velocity
Medium sized wheels = a medium/good amount of rotational velocity
Rotational inertia - an object's resistance to rotate.
The bigger the wheels the bigger the mass and thus the bigger the rotational inertia
The smaller the wheels the smaller the mass and thus the smaller the rotational inertia
Tangential velocity - the linear speed of an object moving along a circular path.
*You want a large tangential velocity, which means the wheels are moving at a fast pace.
*Remember that different sized wheels will have different tangential velocities (example: your car's wheels and your friend's car's wheels). BUT all the wheels on the same car with have the same tangential velocity, just different rotational velocities and rotational inertias, because each wheel is covering the same distance in the same amount of time.
6) We can't calculate the instantaneous speed of the car (potential energy, kinetic energy, or force exerted from the spring) because the force of the spring isn't parallel to the axle spin, so work can't be calculated.
Reflection
1) Our final design was COMPLETELY different than our original. We were trying all the wrong things before any of the right. Our first model was using a cardboard tea box as a body, mason jar tops as wheels, and balloons as the power source. Our final model was using wood as the body, CD's with rubber bands as the wheels, and a lever arm as the source. The promotion of the changes was to test the car, fail, and try something different that would fix that current problem. We just kept encountering issues with the car and making small change after change until we finally applied the correct physics concepts to the car.
2) The major problems with our car was the wheels. They were always either uneven, not touching the ground, not parallel with the axle, or causing the car to drift to one direction more than another. This is why we changed them so many times, but then we figured out that our body was falling apart, thus not allowing our axles to be stable and parallel to each other. So we thought the problem was the wheels (which it was) but the body was also making a big difference in the movement of the car. Once the body was stable, the car started to respond a lot better.
3) If I were to make my car go faster, I would lighten up the body and even out the axles/wheels because I think they were still a little uneven.
4) If I were to do this building process again, I would most definitely do more research. Holt and I just started gathering materials and building without any knowledge of which physics concepts to apply. We should have drawn a model to demonstrate how we wanted to use those concepts, before building the actual model. That would have speeded up the process a significant amount, because we spent a lot of time taking apart the model and rebuilding it.
