Energy systems

Fantastic Elastic

8 Experiment with Rubber Band

Overview

The class decides on two different numbers of turns to give the rubber band. Half the class finds out how far a medium-wheel wind-up goes with each number of turns. The other half does the same experiment with a large-wheel wind-up. Data is collected on class data charts. The class discusses the data and looks for patterns.

Advance Preparation

Photo copy the two Experiments: “Turns of the Rubber Band: Large Wheel Wind-ups” and Turns of the Rubber Band: Medium Wheel Wind-ups” (download below). Make enough copies so half the class has a sheet for the big wheel wind up and half the class has a sheet for the medium wheel wind up.
Make four large sheets on which to collect student data (see samples).
Large and medium wheel wind-ups compared in Lesson 7
Determine the areas to be used for the experiment (a long hallway is best).

Materials

Materials for repairing wind-ups.

Procedure

1.

Class meeting: The purpose of the meeting is for students to review the experiment they will do. This is an experiment to see how far wind-ups (medium and large wheel) will go with a specific number of turns of the stick.

Decide the number of turns: The first question is: “When do we start counting turns?” When wound up, let the wind-up hang down from the stick and unwind freely. When it stops use this as the point from which to begin counting the number of times you turn the rubber band.
How many times should we wind it to make sure it will go? Get different opinions, then try one of the smaller numbers. Increase the number of turns until the large wheel wind-up goes about 10′. Use this number of turns for the first experiments with both wind-ups.
How many times should we wind it to make it go farther? Select a second number of turns for everyone to use, at least 10 turns more than the first. Half of the students will experiment with the large wheel wind-up, half with the medium wheel wind-up. Group for the experiment: Assign groups of four to either the medium wheel experiment or the large wheel experiment.
Distribute the corresponding experiment sheets to each group, one sheet for each student. Students collect data on their own wind-ups.
Go over the experiment sheets quickly. Have students enter the number of turns the class decided upon in the left hand column. Remind them that this is an experiment in which we control the variable of turns. Demonstrate one turn = the stick going around one full time. What will the results tell us?
Each group will know how far a wind up goes with a small number of turns and a large number of turns.
What will we know if we compare the results of a group using the large wheel wind-up to a group experimenting with a medium wheel wind-up?

2.

Experimenting: Assign student groups to spaces and let them begin. Go among the groups to make sure all students are using the numbers of turns decided upon. Look at the data to see if it makes sense, i.e., if more turns is related to the wind-up going further. If the data show fewer turns going further, ask the student if it makes sense. Assist with troubleshooting.

3.

Class meeting: The purpose of the meeting is to collect student wind-up data, compare the data, see if the data make sense, and draw conclusions from the data Medium wheel data: First ask groups who experimented with the medium wheel wind-up: How far did the wind up go with ____ turns (the smaller number). Record the data on the class chart and ask:
Why do you think everyone didn’t get exactly the same result? This is an important discussion of sources of differences. Ask these same groups for their data on how far the wind-ups went with the larger number of turns. Record the data on the second chart and ask: Do you see any pattern between the data on the first chart and the data on the second chart?
Engage the whole class and record any patterns they may see. Large wheel data: Now ask groups who experimented with the large wheel wind-up: How far did the wind up go with ___ turns (the smaller number)? Record the data on the third class chart. Ask these same groups for their data on how far large wheel wind-ups went with the larger number of turns. Record the data on the fourth chart and ask: Do you see any pattern between the data on the third chart and the data on the fourth chart? Again engage the whole class in discussion and record any patterns.

Data on turns of the rubber band

Do you see any patterns when you compare distances traveled by the medium wheel wind-ups with the smaller number of turns (chart 1)to the large wheel wind-up with the smaller number of turns (chart 3)?
Do you see any patterns when you compare distances traveled by the medium wheel wind-ups with the smaller number of turns (chart 2)to the large wheel wind-up with the smaller number of turns (chart 4)?

What conclusions can we make?

Turns of the Rubber Band.doc