7/02/02

Lab Exercise - Kinetic energy

Grizzlies: Bill, Joyce, Jennie

Purpose: To demonstrate the relationship between kinetic energy and work.

Equipment:

Sheet of paper

Pencil, #2, unsharpened

Rubber band, #16

Scotch tape

Steel ball, 8mm diameter

Material necessary to prepare a platform approximately 1dm high

(We used a length of 1x6 and several wood blocks

3 ft. of aluminum foil

Whipped cream

Meter stick

Procedure:

  1. Roll sheet of paper into a tube of 1cm diameter and secure with tape.
  2. Mark pencil in one-centimeter increments, beginning at the unsharpened end.
  3. Secure rubber band to tube at its maximum un-stretched length.
  4. Notch the eraser end of the pencil, rather like an arrow to facilitate keeping the rubber band in place.
  5. Prepare the platform 1 dm high.
  6. Secure tube at the edge of the platform with tape.
  7. Prepare target area. Target area should consist of some type of medium that will stop the projectile. (We used aluminum foil covered with whipped cream.)
  8. Lay meter stick along target area to measure range of projectile.
  9. Insert pencil and ball into tube.
  10. Pull pencil back and launch projectile.
  11. Record the distance “x” that you pulled the pencil back, and the range “R” of the projectile.
  12. Repeat step ten for a minimum of 10 values for x, recording x and R for each.
  13. Compute the work done, “W”, for each trial using the value k = .11 for rubber band. (k can be determined by the students or given by the instructor.)
  14. Plot the data showing the relationship of the R vs. W.

Discussion:

When a spring is compressed or a rubber band is stretched, it can be used to do work. The work done by the spring is given by:

W = -½ kx2

If the spring is released, work done by the spring is given by:

W = ½ kx2

This work can be used to give an object Kinetic Energy.

W =  KE

1/2kx2 = 1/2mv2 - 0

As the amount of work done increases the kinetic energy increases. As the kinetic energy increases the velocity will also increase. If the object is allowed to roll from the edge of a table it will become a projectile. The range of the projectile is determined by the horizontal velocity of the ball. Knowing the range and height of the table the kinetic energy and therefore the work can be determined. This relationship can be used to determine the relationship between work and range.

Questions:

  1. What is the shape of the graph of R vs. W?
  2. Describe the relationship between work and range.
  3. What would the range of the projectile be if the rubber band was stretched 2.5 cm? 5.5cm?
  4. Why is it important that the object be launched horizontally?
  5. List possible sources of error in the design of the launcher. Also state if this error is systematic or random. How can it be reduced or eliminated?
  6. How would your results change if you used a wooden ball instead of steel?
  7. What other labs can be done?

k / x / W / R
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07/03/03

Student Worksheet

Lab Exercise – Kinetic Energy

Grizzlies: Bill, Joyce, Jennie