Classroom Activity for 14-16
What the Activity is for
Experiencing constant and varying forces.
This series of explorations paves the way for the quantification of forces. Questions such as these begin to mean something to students as they can be related to their own experiences.
Value: How big is this force in newtons?
Vary: How does this force change as I change this?
What to Prepare
- a feeling force board
- a length of thin shock cord
- a foam ball
- a pencil and some plain paper
- some safety glasses
Safety note: As the stretched shock cord can spring back rather suddenly when it snaps, safety glasses should be worn.
What Happens During this Activity
The forces board can profitably be firmly mounted at the side of the classroom, and used opportunistically, with individuals or groups invited to go up and experience exerting 1 newton or 10 newton.
Each student should have the chance to stretch the band and to squeeze the ball. They should then sketch out the shape of the force-extension graph. The axes should be left blank at this stage. For this reason we'd suggest not using graph (or even lined) paper.
That forces acting may change systematically depending on the systematic changes in the environment is the first notable outcome.
Small groups should then compare their sketches.
If there is disagreement, so much the better.
From these differences can evolve a useful discussion of how such arguments are settled, so long as you resist the temptation to
give the answer. (The reason for using the shock cord and foam ball is that it heads off suggestions that the answer can be looked up – say in a textbook or online).
Do allow time for a consensus to emerge, and for comparison with the sketch graphs.
Settling differences of opinion by making measurements
If you are going to go down this route, you'd better be prepared for further investigation. Collect together apparatus for the appropriate number of groups:
- some graph paper
- hanger masses matched to the shock cord chosen
- retort stand, boss and clamp
- a G-clamp
- a metre ruler
This is a time for careful, skilful experimentation. The results need to be reliable and checked with other groups. You might plan for that by arranging for the plots to be displayed on a wall, or to some standard scales, to allow easy comparison.