Thursday, January 28, 2016

Information and Background

In this lab the students calculate the potential energy of their Hot Wheels car at the top of a track and then calculate the kinetic energy of the car at the bottom of the track.  The students then compare these and discuss why they are not the same in the context of the Law of Conservation of Energy. This lab could be carried out very simply with a straight orange track set-up, but I've chosen a little bit different way to go about it.  In my physics class we not only focus on the science concepts, but I also like to get the students involved in design and engineering.  So for this lab the students design and build a "Roller Coaster Track" that the cars roll down.  It does take extra time that all teachers may not have, but I think the critical thinking and problem solving the students do are worth the time that we spend.  I give the students a few pieces of straight orange track to use, but the rest of the roller coaster track must be made from paper and tape, even the curves.  I love the problem solving and thinking that the students use to figure out how to make the paper do what they want it to do and bend how they want it to bend, and support what they want it to support.  There are other things that may be easier to use, but I like the challenge of building it out of paper.  The things you would need for this lab are paper, tape, Hot Wheels cars, orange track, and a stopwatch.  In recent years I have acquired a photogate to help calculate the velocity of the car at the bottom, but previously just used a stopwatch and a distance.  I'll discuss these options and more in the Notes after presenting the lab.

The Lab

Purpose:
The students will investigate Potential and Kinetic Energy while designing and constructing a paper roller coaster track.

Procedure:
Build a roller coaster out of paper, tape and Hot Wheels track. Use the following design criteria:
• Each roller coaster must include at least:
• 3 turns of at least 90 degrees separated by a straight section.
• 2 uphill sections no shorter than 2 car lengths
• The car must stay on the track through the whole roller coaster.
• The roller coaster cannot be touched during the test.
• Your coaster must be stable. The track should not move or shake when the car travels along the track.
• Your coaster should end with a flat section on the ground. (This design aspect is so that we can do some calculations regarding the Conservation of Energy)
Data:
Use the photogate to determine the velocity at the bottom of the roller coaster. Record the Velocity.

Analysis:

• Calculate the Potential Energy (PE) of your car before it starts.

• Calculate what the Kinetic Energy (KE) of your car should be when it finishes. This is the THEORETICAL KE.

• Calculate the average velocity from TABLE 1.

• Using the average velocity, calculate the actual Kinetic Energy of the car when it finishes.

• The Law of Conservation of Energy says that the kinetic energy (KE) when the car finishes should be equal to the potential energy (PE) before the car starts. Meaning PE = KE. In the actual experiment does PE = KE? Was energy lost or gained?

• Calculate the percent of energy lost?

• Where did the energy that was lost go?

• What could you have done to minimize the amount of energy lost?

Conclusion:
Discuss this project and its relationship to potential and kinetic energy. Discuss the law of conservation of energy and how it relates to this project. Make sure you discuss what you did do or could do in the future to minimize the loss of energy in your Roller coaster track.

Notes

• To calculate the Kinetic Energy of the car at the bottom of the roller coaster track, the students need to know the velocity of the car at the bottom of the roller coaster track.  A low tech solution (which I used in the past) is to put a few feet of track at the bottom for the car to roll on and then time the car for those few feet.  Calculate the velocity of the car by dividing the distance by the time.  I recently acquired a photogate and I am able to get the velocity of the car pretty accurately with that. Another option you could use to get the velocity of the car is the Hot Wheels Speedometer.  The Hot Wheels Speedometer gives you a scale speed in miles per hour so you would need to divide by 64 and convert it to whatever units you were using in your energy calculations.
• Here are a couple of pictures that I show the students to give them a vision of what can be done with paper.  The roller coasters are for marbles, but it gives them some ideas.

• The students almost always discuss the loss of energy due to friction, but another big loss of energy that I make students aware of is that due to movement of the roller coaster.  I always point out that if the roller coaster is moving as the car goes down the track then you are losing energy.  It takes energy to move things and if your roller coaster is moving, it took energy to do that and that energy is coming from your car. The more sturdy they can build their roller coaster, the more energy that will be conserved.

1 comment:

1. Thank you so much, I am very excited to try this lab.