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Energy in motion
Building a Really Big Mousetrap Car
(that isn’t actually a mousetrap car)
The car’s frame is wood and it’s wheels are bike wheels. The axles are PVC pipe slided into slightly larger PVC pipe. The tower in the center is designed to lift up a heavy weight that can be seen on the table in the far left of the frame (currently the weight is a cement block and a plastic container full of rocks) Twine is attached to the weight, wrapped around a pulley on the tower and then bolted to the back axle. The Idea was that the weight of the Cement block and Rocks would pull on the twine, which would pull on the axle, causing it to turn.
Data/Observations:
Test
Observations / Data
Pre-Test 1: Strength
The car’s strength was tested by running the pulley system with two containers full of rocks. In the first test, the pulley that was attached with duct tape fell off. It was then replaced using screws and an extra piece of wood.
Pre-Test 2: Strength
When the pulley was fixed and the test was repeated, the upright board snapped. It was replaced with a stronger and denser piece of wood.
Pre-Test 3: Strength
The weight that broke the upright board then broke the middle board it was put on. The new board was much wider and denser.
Test 1: Outside
Because the car was on a slight incline and a smooth surface, it was able to go 18 meters at 0.6 m/s.
Test 2: Inside, 3 m Velocity
The floor was slightly uneven and resulted in the car staying still until pushed. When given a small push, it had an average velocity of 0.3 m/s.
Test 3: Inside, 3 m Velocity
The conditions from test 2 were replicated, and the car went 0.375 m/s.
Test 4: Inside, 3 m Velocity
In this test, the car had the average velocity of 0.43.
Test 5: Inside, Distance and Accuracy
The car, when pushed, covered 5.5 meters. The displacement from it’s course was 0.2 meters.
Test 6: Inside, Distance and Accuracy
The car traveled 3 meters with a course displacement of 0 meters.
Test 7: Inside, Distance and Accuracy
The distance the car went was 8 meters and it had a displacement of 0.4 meters.
Analysis and Discussion: Our original design involved using a bungee cord to store enough energy to move our car, but we abandoned the idea in favor of another source of power that could put out a more consistent force. We decided to use a weight attached to a pulley system to move the car. The weight held an impressive amount of potential energy at 6174 kilojoules. Unfortunately, because the twine had to go through the pulley system, a lot of the force exerted on the car by the weight ended up weighing the car down, instead of pushing it forward. The weight was negated by the normal force of the car, but by the time the force reached the axle, it wasn’t a lot of force. For a while, our solution was simply to add more weight, but this proved extremely inefficient because under the new amount of weight the frame would sag and snap. The car is still being worked on, and the current plan is to decrease the axle to wheel circumference ratio, trading out maximum distance for the torque needed to make the car move.
Objective met or not, and why: The objective is currently not met, although the car is still being worked on. An early design of the car did work, and went an impressive 18 meters, but we were unable to recreate our results on a less flat and inclined surface. Our goal changed to make the car work in less desirable conditions, and modifications are still underway.
Explanation of the physics behind your design changes: Our original power source was going to be a bungie cord. We abandoned it because the Elastic potential energy of even a 60 cm bungee cord wasn’t nearly as much as the potential energy of the gravitational potential energy of a heavy weight suspended 155 cm above the ground. We are currently deciding whether to go back on the decision because so much of the potential energy is negated by the normal force of the car. When our car didn’t work on a slightly sloped surface, we decided to increase the torque by increasing the weight. Because of that, as our car’s weight was increased to give more torque, we also added more reinforcements to the center tower, to provide more normal force to counter the increased weight and keep the frame of the car from breaking. While this did increase the
Future predictions for a different objective: Our current goal is to increase the torque. Currently, the millions of joules that are stored in the weight are being spent overcoming the normal force of the pulleys. We predict that if we use bungee cord instead of the pulley system, the replacement of gravitational potential energy for elastic potential energy will allow more joules to be spent on the turning of the axle. This will give our car enough torque to overcome the uneven surface.
Data/Observations:
Test
Observations / Data
Pre-Test 1: Strength
The car’s strength was tested by running the pulley system with two containers full of rocks. In the first test, the pulley that was attached with duct tape fell off. It was then replaced using screws and an extra piece of wood.
Pre-Test 2: Strength
When the pulley was fixed and the test was repeated, the upright board snapped. It was replaced with a stronger and denser piece of wood.
Pre-Test 3: Strength
The weight that broke the upright board then broke the middle board it was put on. The new board was much wider and denser.
Test 1: Outside
Because the car was on a slight incline and a smooth surface, it was able to go 18 meters at 0.6 m/s.
Test 2: Inside, 3 m Velocity
The floor was slightly uneven and resulted in the car staying still until pushed. When given a small push, it had an average velocity of 0.3 m/s.
Test 3: Inside, 3 m Velocity
The conditions from test 2 were replicated, and the car went 0.375 m/s.
Test 4: Inside, 3 m Velocity
In this test, the car had the average velocity of 0.43.
Test 5: Inside, Distance and Accuracy
The car, when pushed, covered 5.5 meters. The displacement from it’s course was 0.2 meters.
Test 6: Inside, Distance and Accuracy
The car traveled 3 meters with a course displacement of 0 meters.
Test 7: Inside, Distance and Accuracy
The distance the car went was 8 meters and it had a displacement of 0.4 meters.
Analysis and Discussion: Our original design involved using a bungee cord to store enough energy to move our car, but we abandoned the idea in favor of another source of power that could put out a more consistent force. We decided to use a weight attached to a pulley system to move the car. The weight held an impressive amount of potential energy at 6174 kilojoules. Unfortunately, because the twine had to go through the pulley system, a lot of the force exerted on the car by the weight ended up weighing the car down, instead of pushing it forward. The weight was negated by the normal force of the car, but by the time the force reached the axle, it wasn’t a lot of force. For a while, our solution was simply to add more weight, but this proved extremely inefficient because under the new amount of weight the frame would sag and snap. The car is still being worked on, and the current plan is to decrease the axle to wheel circumference ratio, trading out maximum distance for the torque needed to make the car move.
Objective met or not, and why: The objective is currently not met, although the car is still being worked on. An early design of the car did work, and went an impressive 18 meters, but we were unable to recreate our results on a less flat and inclined surface. Our goal changed to make the car work in less desirable conditions, and modifications are still underway.
Explanation of the physics behind your design changes: Our original power source was going to be a bungie cord. We abandoned it because the Elastic potential energy of even a 60 cm bungee cord wasn’t nearly as much as the potential energy of the gravitational potential energy of a heavy weight suspended 155 cm above the ground. We are currently deciding whether to go back on the decision because so much of the potential energy is negated by the normal force of the car. When our car didn’t work on a slightly sloped surface, we decided to increase the torque by increasing the weight. Because of that, as our car’s weight was increased to give more torque, we also added more reinforcements to the center tower, to provide more normal force to counter the increased weight and keep the frame of the car from breaking. While this did increase the
Future predictions for a different objective: Our current goal is to increase the torque. Currently, the millions of joules that are stored in the weight are being spent overcoming the normal force of the pulleys. We predict that if we use bungee cord instead of the pulley system, the replacement of gravitational potential energy for elastic potential energy will allow more joules to be spent on the turning of the axle. This will give our car enough torque to overcome the uneven surface.