Ball Bounce Lab

Problem:

How does the height from which a ball is dropped affect the height to which it bounces after hitting a hard surface?

Materials:

Various balls (super balls, basketballs, playground balls, tennis balls, golf balls or other), brick wall made of cinder blocks, groups of two or three students, graph paper

Procedure:

1.  The experiment should be done near a cinder block (or brick) wall so that the distances can be estimated to the nearest fourth (1/4, 1/2, 3/4, 1) of a cinder block. Some time should be spent in the beginning to practice estimating distances this way.

2.  Divide the activities so that one student drops the ball, one student watches the bounce and estimates the height to which it bounces, and one student records the data.

3.  Drop a super ball from various heights. Estimate the height to which the ball bounces as carefully as possible. Both the height of drop and the height of bounce should be recorded.

4.  Drop the ball at least two times from each height with the average of the bounce heights used as the final measurement. If there is too much variation in these two measurements, take a third measurement.

5.  Drop the ball from at least six different heights beginning at about two blocks. Increase the height of drop one block at a time until six or more drops have been completed.

6.  Care must be taken in doing the estimations. Decide as a team what you might do to make the measurements as accurate as possible. Document the process you decide to use to measure the ball’s position.

Data Analysis:

7.  Draw a graph bounce height vs. drop height.

8.  Draw a best fit line for the data points. Note: This is NOT a line drawn to connect each point. It is a line which best shows the relationship involved - in this case a straight line.

9.  Compute the slope of the best fit line. Note: this is NOT the slope between the first and last data point. 10. Write the equation for the line using the slope-intercept form (y = mx + b). The line of the graph may not go through the origin as the bottom cinder block may be elevated above the floor.

10.  Use the graph to predict the height of the bounce for a ball dropped half way between two drop heights. This is called interpolation.

11.  Use your graph to predict the height of the bounce for a ball dropped from twenty or thirty bricks high. This is called extrapolation.

12.  Use the graph to predict the height of the bounce for a ball dropped half way between two drop heights. This is called interpolation.

13.  Use your graph to predict the height of the bounce for a ball dropped from twenty or thirty bricks high. This is called extrapolation.

14.  Test the predictions by dropping the ball from the chosen heights and measuring the bounce. Compare your predictions with the results from testing. Check with other groups and see if their results are similar to yours.

15.  What do you conclude about the accuracy of information found from a graph by interpolating between data points and extrapolating beyond them?

Data Chart A

Drop
Height / Bounce Height
#1 / Bounce Height
#2 / Bounce Height
#3 / Average of Bounce Heights
Height 1
Height 2
Height 3
Height 4
Height 5
Height 6

Data Chart 2

Prediction / Test Results / Difference
Value between data points
Value beyond data points


Ball Bounce Lab

Teacher Notes

Most teachers do not use the printed lab sheets that have been provided. They simply describe the purpose of the lab and let students decide how to find the information and present it on a data chart. This method is a discovery approach to the lab and works quite well. The printed lab sheets are provided in case the teacher wants to use them.

This lab is best used early in the year. This is a great time to review techniques of making and interpreting graphs. The graphs should be done on graph paper, not just sketched on notebook paper. One or two groups should put their graphs on a transparency or a graph paper section of the chalk board so that the entire class can see them for the discussion.

One of the purposes of this lab is to help students understand that standard measurements such as the meter are only standard because everyone agrees that it is the standard. Many things can be used as a measuring instrument as long as the divisions are equal – in this case blocks on a wall. A discussion of various early measurements such as the cubit, which was the distance from the carpenter’s elbow to the end of his fingers, can help. The cubit worked just fine as long as there was only one carpenter working on the building.

It is not necessary to give the students a formal write-up of this lab. One has been provided if you want it, but most teachers do not use it. They simply describe the procedure, tell students to make a data chart, give them a ball & send them out to do the experiment. The ideal situation is for the students to discover for themselves such things as doing each height several times and being consistent about how they judge the height of the ball.

Some of the newer schools may not have exposed cinder block or brick walls even on the outside of the building. In that case, some ingenuity may be required. Adding machine tape (or dry wall tape) marked with heavy marker about every 15 cm and then taped to a wall would be one solution. The important thing is for the divisions to be fairly large so that the groundwork has been laid for a discussion of the precision of a measuring instrument.(See activity 3 Accuracy and Precision). That discussion can come immediately after this lab or at a later date. The Ball Bounce Lab can be referred back to when the discussion is held.

The data from the balls will produce a straight line for reasonable heights. One important point is that when the ball is dropped from a greater distance, the straight line no longer holds. The coefficient of restitution of the balls (even super balls) breaks down when the ball is dropped from heights of around 15 cinder blocks. The students actually see for themselves that interpolation within the range of the data is much more accurate than extrapolation outside the range of data.

Most of the lab can be used with students from 9th grade to 12th grade regardless of their math skills – the part about computing the slope and the equation of the line can be omitted without losing the import of the lab.

Adapted with permission from the Comprehensive Conceptual Curriculum for Physics (C3P), Richard P. Olenick, University of Dallas, Irving, TX (2000). Copyright 2000 by Richard P. Olenick, University of Dallas.

Diagram drawn by Russel; Davison, King High School, Tampa, Florida