# WORK LAB

When we are discussing work, either we, gravity, friction, or some other source provides the work that is done in a given situation. In this series of labs, an object will be moved by the application of work from a source. As a result of that work, a change in its state of energy will occur. We want to compare the results of analysis of work and energy to determine if we have the basis of a physical law.

### Purpose

• Calculate work carefully during an experiment
• Calculate the energy change(s) that occur(s)
• Compare the respective sizes of the changes which occur

### Procedure

Conduct the experiment outlined. On the basis of visual observations, describe the nature of the work that occurs as well as the changes in energy.

Repeat the experiment, gathering specific data for position, velocity, acceleration and force.

Spreadsheets can be set up with Excel, or they can be set up within the interface programs themselves by making new columns and having the program do necessary calculations. For example, you could take a quantity equal to 1/2 the mass and multiply it times velocity squared to get a column of kinetic energy.

### Analysis

1. Calculate any work that occurs during your experiment. Note that this may involve finding the integral of the Force vs. Position graph.

2. Calculate any change(s) in energy that occur.

3. Compare the sizes of the quantities asked for above. Use percentage difference as a measure of how close they are to one another.

### Report

Prepare an oral report, to present to the class. Include the following portions, as the rest of the class may not be fully aware of your experimental procedure:
• Procedure
• Observations
• Calculations
• Graphs
• Discussion of Results, Analysis & Conclusions

Use prepared visual materials to assist you in your presentation. We will be able to project Powerpoint presentations should you choose to partake. You will have 7 minutes for your basic report, and an additional 2 minutes for questions.

 . Experiment Description Equipment Setup A B You will release a lab cart from near the top of an inclined track. Monitor its motion along the track and set up a spreadsheet that calculates the work done and the resulting kinetic energy. Dynamics Track Dynamics Cart Sonic Motion Sensor Interface C D E You will release a rolling object (ball, cylinder or other object) from near the top of an inclined track. Monitor its motion along the track and set up a spreadsheet that calculates the work done and the resulting kinetic energy. Rolling Object* Track Sonic Motion Sensor Interface C = Ball D = Cylinder E = Toy F G Pull the lab cart away from the force sensor, which is attached to the cart with a long rubber band. Release the cart and calculate the work done and the kinetic energy that develops. Lab Cart Rubber Band Force Sensor Motion Sensor Interface H I Place a mass on the end of a hanging spring. The position where it no longer moves up and down is its equilibrium point. Displace it up or down from that point. Set up a spread sheet to monitor the kinetic, gravitational potential and elastic potential energies throughout a complete cycle of motion. Spring Mass Motion Sensor Interface J K Place a glider on an inclined air track and attach it to a light spring. With the air flowing, the position where the glider no longer goes down the track, but sits still is its equilibrium point. Displace it up or down the track from that point. Set up a spread sheet to monitor the kinetic, gravitational potential and elastic potential energies throughout a complete cycle of motion. Spring Glider Air Track Motion Sensor Interface

NOTES:

A/B:

For this lab, you will use a roller skate cart which was state of the art 30 years ago. It should be more interesting than the almost friction-free cart that you're used to using.

C/D/E:

In groups C and D, you will be provided with two different objects with similar shapes. They are somewhat different, though, and your results from one should be compared with the results from the other. Some additional outside research may be needed.
Group E should obtain results from group C as a comparison for the results they get with their rolling object.

F/G:

Group F should conduct the experiment using a level track, while Group G should have the track inclined so the rubber band pulls the cart up the track.
The Force Sensor needs to be calibrated. Hang a mass on a string passing over a pulley. If you use 500 grams, the force will be 4.9 newtons.
You will use a long rubber band that will be provided, and should use the two extra masses in your cart to make a combined mass of around 1500 grams.
The time for this lab to unfold is relatively short. You may need to adjust the time in the program down to see the details more clearly.

H/I:

Use two to four different masses hung from the spring to establish the spring constant.
In an ideal world, the total energy in a conservative system (such as the one you have here) should remain constant. That should be your goal, and you may need to experiment in order to determine where the zero point is for UE to achieve that goal.

J/K:

Please do not stretch the spring beyond its elastic limit. A gentle movement back and forth is sufficient to gather the data in this experiment.

Updated 11/15/97.