Forces and Motion

Close the door!

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

This is a short demonstration to show the relationship between force, length from pivot to the line of action of the force, and turning effect in the context of closing a door.

What to Prepare

  • Gather the class around the lab door

What Happens During this Activity

With suitable gravitas the teacher announces that today's first activity will involve the famous physics experiment of closing the lab door!

Invite one pupil to see if they can achieve the impossible and close the door. They do so! Can they do it with one finger? They can! Now ask them to push half way across the door. What about the size of the push needed? It's bigger. With one finger? Yes!

Now ask them to push on the door at a point very close to the hinges. Can they still close it with just one finger? Maybe just, but a much bigger push is needed.

It seems that to close the door you need to take account of both the size of the push and where you push:

  • If you push a long way from the hinges, only a small force is needed.
  • If you push close to the hinges, a much bigger force is needed.

So the scene is set for thinking about levers in general.

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