Pre-Engineering Physics

Conservation of Energy Lab-Energy of a Bouncing Ball

 

 

When a basketball player bounces a ball straight down, it speeds up until it bounces of the floor and then slows down as it rises back to the top of it’s path.  In terms of energy, when the ball is at the top of its path it has all potential energy, PE.  When the ball is falling to the ground, the potential energy is changing into kinetic energy KE.  Midway between the top of the path and the ground, the ball possesses KE and PE combined.   At the bottom of the path, the ball possesses all kinetic energy.  This cyclic process is repeated, up and down, energy changing from one form into another. 

 

If there is no work done by frictional forces, the total energy will remain constant from one cycle to the next.  In this experiment, conservation of energy will be studied to see if this works out for the bouncing of a ball.  The study of these energy changes will be accomplished using a Motion Detector/CBR and TI-84 graphing calculator. 

 

Problem ID:  Is energy conserved in a bouncing ball? 

 

Preliminary questions: (8 points)

 

  1. What form or forms of energy does a ball have while momentarily at rest at the top of its path?

 

 

  1. What form or forms of energy does a ball have right before contact with the floor at the bottom of its path?  

 

 

  1. What form or forms of energy does a ball have while in motion in the middle point of its path?

 

 

  1. If there are no frictional forces acting on the ball, how is the change in the ball’s potential energy related to the change in kinetic energy? 

 

 

 

 

 

 

 

 

 

 

Procedure:

  1. Measure and record the mass of the ball in the data table following.
  2. Connect the CBR to the calculator. 
  3. To collect data of a bouncing ball, under APPS in the calculator, select CBL/CBR, then RANGER.
  4. Under the MAIN MENU select APPLICATIONS, UNITS/METERS, then BALL BOUNCE.
  5. Follow the directions from the calculator screen.  The key to collecting acceptable involve holding the CBR steady at 1.5 m above the floor, and then hold the ball 0.5 m underneath the CBR before dropping. 

 

Collect data until it looks similar to the following sample curve. 

Notice that height (m) is on the y-axis and t (s) is on x-axis; also note that the bottom of the parabolas come back to x=0 each time. 

Once acceptable data is collected, perform screen capture with TI Connect and USB cable to use for data presentation.  Paste this curve into a Word document and print a copy of the curve for each lab member.  Label the approximate points (t,h) along the curve that are used in energy calculations (18 points).  Save the screen to complete the instructions below. 

Use the TRACE key to follow along the curve and select points for analysis.  Use the largest and most complete parabola.  Along this parabola, collect the h and t values for 5 specific points.  (Select curves where bottom of parabolas are really close to x-axis.)

These five points should coincide with the following positions:

  1. bottom of first and largest parabola
  2. midpoint along left side of first parabola
  3. top of first parabola
  4. midpoint along right side of first parabola
  5. bottom point on right side of first parabola, which is also the bottom of left side of second parabola

Fill in the Data Table with the appropriate time and height values, then perform the other calculations to complete the table.  Use this information to address the questions in the Conclusion.  Use the velocity-time graph to trace across curve and collect velocity values.  When ball is moving up v(+) and moving down v(-).

Pick maximum velocity value to correspond with lowest (zero) height and minimum velocity value to correspond with highest height. 

 

Data Table

Mass of the ball

(kg)

 

(32 points)

Position

Time (s)

Height (m)

Velocity (m/s)

PE (J)

KE (J)

Total Energy (J)

1. bottom left

 

 

 

 

 

 

 

 

2. midway of left side

 

 

 

 

 

 

 

3. top of parabola

 

 

 

 

 

 

 

 

4. midway of right side

 

 

 

 

 

 

 

5. bottom right

 

 

 

 

 

 

 

 

(compare maximum total energies-the top of the bounces)

 

Conclusions

Does the total energy remain constant?

Should the total energy remain constant? Why? If it does not, what sources of extra energy are there or where could the missing energy have gone? 

 

 

Where are the maximum and minimum values for PE and KE, and to what position of the ball do they correspond? 

 

 

 

 

 

Address these questions in terms of transfer of energy from one form into another and what is going on in terms of conservation.  (10 points)