Introduction: The purpose of this exploration is to compare the work done on an object to the change in kinetic energy of the object by using the Force Sensor to measure the force applied to the cart, and the Photogate/Pulley System to measure the motion of the cart as it is pulled by the weight of the hanging mass.
Most people expect that if you do work, you get something as a result. In physics, when a net force performs work on an object. The result is a change in the energy of the object. The relationship that relates work to the change in kinetic energy is known as the work-energy theorem. This theorem is obtained by bringing together three basic concepts: NewtonÕs Second Law, work, and the equations of kinematics.
Purpose: How does the amount of work done on an object to make it move in the horizontal direction compare to the amount of kinetic energy gained by the object?
Materials:
| PASPORT Force Sensor | Balance |
| PASSPORT Photogate Port | Mass and Hanger Set |
| Power Link | Photogate/Pulley System |
| 1.2 m track with bumper | Dynamic Cart |
| 1.2m String |
Procedures:
Set Up:
1) Plug USB powerlink into computer
2) Plug in the force sensor and the photogate sensor
3) Determine the mass of your cart system with mass and force sensor on top. You may have to weigh each part separately. RECORD.
4) Attach the force sensor to the cart with the screw so the hook is facing outward
5) Attach the photogate/pulley system to the end of the ramp
6) Tie a string around the force sensor, around the pulley, and attach the other end to the mass holder
7) Make sure track is level by placing cart on track until it doesnÕt move without a force.
8) Go to Applications and select the Data Studio Folder --> Open up Data Studio --> eLabs --> Conceptual Physics --> CP Configuration files --> CP Work Energy CF (This should start Data Studio automatically, if not, open Data Studio from the applications folder then choose "open activity" and follow the same path to the CP Work Energy CF file)
9) Choose smartpulley ÒlinearÓ .
10)Accept the default value for spoke spacing if prompted.
11) Move the graph window so you can see the one underneath it. You should have TWO graphs, one with Force and time and the other with Position, velocity, and time.
Get Data:
1. Zero force sensor with no mass pulling on it.
2. Add a known mass to the end of the string. RECORD.
3. Hold onto cart and then start recording data just before cart is released.
4. Stop cart BEFORE it hits the photogate.
5. Repeat for a total of three trials.
6. For each run, record the maximum position and velocity, and the average (mean) force.
Data:
Mass of cart with force sensor:________ kg Mass at end of string ______ kg
|
Trial
|
Mean Force (N)
|
Max position (m)
|
Max velocity (m/s)
|
Max KE (J)
|
Work (J)
|
|
1
|
. | . | . | . | . |
|
2
|
. | . | . | . | . |
|
3
|
. | . | . | . | . |
Calculations:
For each run, calculate Max KE, Work, and % relative error. Show 1 sample calculation below for each:
|
Max KE
|
Work
|
% relative error
|
| . | . | Trial 1:
|
Questions:
1. How does the work and maximum KE compare? __________ Why? _________________________________________________________
2. Write an equation relating KE max and Work ______________________
3.  Rewrite the equation using F, d, m, and v. _________________________
4.  How do you know when work is being done? ______________________
5. How does the WEIGHT of the mass at the end of the string compare to the mean force? Why? _____________________________
6. Use the above equations to determine how fast a 20 kg car will move if its engine provides a 1000 N of force over 500 m. (USE 5 STEPS!!!!) ___________