Newton's Law of Gravitation
Earth and Space

Beam hanging

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

This activity provides a memorable experience relating to the gravitational pull of the Earth and establishes that objects fall because of the external action of gravity.

What to Prepare

  • horizontal beams (this activity involves pupils hanging by their hands and arms from a horizontal beam and the best place for the lesson is the school gymnasium or sports hall – remember to check availability).
  • stop watch
  • clip-board

Safety note: Check with the PE department as to the safe working load of the beam and how to secure it safely in position. Use the minimum height possible. Beware of excessive competition leading to muscle damage. Do not attempt to improvise a beam in any other location (e.g. using the suspension beam in a physics laboratory).

What Happens During this Activity

The build up to the beam-hanging activity involves introducing and talking through the strange property of gravity, that it acts at a distance. The idea then is to get the pupils into a situation where they are away from the Earth's surface and being attracted towards it.

This is easily achieved by getting the pupils to hang on to a horizontal beam with their hands, such that their feet are just clear of the ground. You might organise the activity such that five or so pupils of similar height hang from the beam at once and the big challenge is to:

Battle the pull of gravity for as long as you can!

The spectacle is quite something! As the pupils hang from the beam, sweat pouring from their brows, pass up and down the line asking:

Teacher: Can you feel the pull of gravity? Can you feel it pulling you down?

(Some might refer to this as kinaesthetic learning.)

Many classes like to engage in this activity as a competition, with no shortage of volunteers to participate. Experience has shown that the competition is often won by relatively small and wiry pupils who appear to have the capacity to withstand the pull of gravity for as long as they like! It is the stronger boys who struggle to withstand the greater pull of the Earth on their more massive bodies much to their obvious embarrassment, and to the delight of others.

Newton's Law of Gravitation
is expressed by the relation F=G(m_1)(m_2)/r^2
can be used to derive Kepler's First Law
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