Forces in action

Inside, outside, action and reaction. Part of how things work.

Forces in action

Inside, outside, action and reaction · Alberta Grade 6 · maddyhelps.com

Name
Date

Tick the internal force in each object: tension (pulled), compression (squeezed), shear (pushed in opposite directions) or torsion (twisted). Then name each external force, and answer the last two.

Object	Tension	Compression	Shear	Torsion
Pulling on a rope in tug-of-war
Standing on an empty pop can
Scissors cutting paper
Wringing out a wet towel
A hole punch going through paper
The chain holding up a swing

Your hand pushing a sled: which external force?

Snow slowing the sled down: which external force?

A trampoline pushing you back up: which external force?

A paper clip bent open: a plastic or an elastic change?

An elastic band stretched and let go: a plastic or an elastic change?

On skates, you push against the boards with your hands. Which way do you move, and why?

For the grown-up

Forces in action

“Pulling on a rope in…” tension; “Standing on an empty pop…” compression; “Scissors cutting paper…” shear; “Wringing out a wet towel…” torsion; “A hole punch going through…” shear; “The chain holding up a…” tension. External: your hand pushing a sled — applied force; snow slowing the sled down — friction; a trampoline pushing you back up — elastic force. A paper clip bent open — plastic; An elastic band stretched and let go — elastic. Skates: you move away from the boards. You push the boards (the action) and the boards push back on you just as hard in the opposite direction (the reaction) — Newton's third law.

Shear and torsion are the two children find hardest to picture. Scissors are shear: the blades push the paper in opposite directions along a line. Wringing a towel is torsion: the two ends are twisted opposite ways.

Why this matters is on the how things work page. More sheets