#194. Clever Levers

Science, level: Middle
Posted by Kjackson (kjackson@cc.memphis.edu).
Univ. of Memphis, Memphis, Shelby
Materials Required: 1 meter stick, 3 large paper clips, paper cup, masking tape, pencil, 2 rulers, rubber band, masses
Activity Time: 1 Class Period
Concepts Taught: Levers help to lift loads with less effort.

Key Question: When using a lever with the least amount of effort where should the load and the effort be placed?

Procedure:

1. Discuss key vocabulary and the Law of Conservation of Energy.
2. Distribute the materials along with the chart.
3. Build the lever using the following instructions:
a). Open a paper clip into an "S", and tape it perpendicular to a meter stick at the 10 cm mark. Tape it
so tht the larger end of the S sticks out above the top of the meter stick.
b). Tape a pencil to the top of the table so that the end with the erases sticks out 2 cm.
c). Hang the meter stick by the end of the paper clip on the end of the pencil. This is the fulcrum of
the lever.
d). Slip the rubber band into one of the hooks of another paper clip. Slide the rubber band onto the end
end of the meter stick opposite the pencil until it is at the 90 cm mark. Tape the paper clip to the
top of a table so it supports the meter stick by the rubber band. Make sure the rubber band is still
at the 90 cm mark before you tape it down. This is where the effort on the lever will be measured.
e). Bend a third paper clip into an "S". Poke the smaller hook into a paper cup just below the rim. Add
weight to the cup as instructed by the teacher. By hanging the big hook on the meter stick you will
be putting the resistance on the lever.
4. Measure the length of the rubber band before adding resistance. Measure to the nearest mm and record the
length on the chart beside total stretch and under Lever with no Resistance.
5. Hang the cup with its mass at the fulcrum. Measure and record the total stretch of the rubber band and
calculate the net stretch (total stretch minus stretch with no resistance). Although you will read these
measurements in mm, they will be recorded in rubber band units.
6. Move the resistance 200mm. measure and record the total stretch, and calculate the net stretch.
7. Make a line graph using values for the total stretch from your data.
8. Graph the net stretch as a second line on the graph. Label both lines.
9. Discuss the results from the graph and make conclusions based on the results. Also, answer key question
based on data gained.