Forces and Motion

Model doors

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

Building model doors: a quick experiment to get a feel for the differing effects of the action of a force applied at different lengths from the pivot.

To get some experience of making and manipulating a physical model.

To appreciate the care that must be taken in order to use the results from the model to make predictions about real behaviour, and to understand the system.

What to Prepare

  • small rectangles of aluminium sheet, approximately 10 centimetre by 4 centimetre (other rigid rectangles could be substituted – but do ensure that the edges are smooth)

What Happens During this Activity

Work in pairs. One pupil acts as the door hinge, gripping one end of the rectangle between finger and thumb. The other tries to open the door by pushing with a single finger.

You might ask the pair to model the following situations, recording their actions for a discussion by a simple plan view sketch.

  • Opening a door by pushing near the hinge.
  • Opening a door by pushing in the middle.
  • Opening a door by pushing as far from the hinge as possible.

From these three, they should be able to say something about the relative difficulty of opening the door, provided they have designed their experiments with care (kept the same hinges). Asking what they have done to make their findings reliable should allow them to identify this as the significant factor.

We suggest you concentrate on the balance between the force their finger exerts on the door and lengths to the pivot as the two key factors to draw out.

Then you might ask them to model hinges that make the door harder to open. (Careful experimenters will find two ways to do this: By gripping harder, and by sliding the finger and thumb farther up the door. You might manage to make something of this, drawing out the effects of force and length for the hinge as well as for the finger doing the opening).

Teacher Tip: A digital camera and an interactive white-board could provide a large image for a chosen pair to explain their experiment to the class.

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