Force
Forces and Motion

Bigger and faster

Classroom Activity for 5-11 Supporting Physics Teaching

What the Activity is for

Do heavier objects fall faster? The purpose of this activity is to challenge the commonly held, but mistaken, idea that heavier objects necessarily fall faster than lighter objects. The detailed reasoning is for the future, but a start on establishing some thinking along the right lines can be made now.

What to Prepare

  • Two blocks of wood, one at least double the mass of the other
  • Two items of soft fruit – we'd suggest a melon and a peach
  • A chair, ladder or balcony to give you a free-fall distance of at least 2 metre (more is better, but messier)

What Happens During this Activity

Start with hefting the blocks of wood.

Encourage children to predict which of two blocks will hit the ground first when released together from the same height. Allowing children to feel the different masses before release is important. Encouraging a dialogue about which of the two is being pulled with a greater force is also important.

It is likely that a range of predictions will emerge from the class. Invite children to share their reasoning for these predictions before they see the event.

Safety note: Take care when dropping heavy objects. Bouncing masses can be dangerous, as indeed can be falling ones. Two blocks of wood, about 200 gram and 800 gram, will do the trick and will not be adversely affected by wind resistance over a fall of a few metres.

Dropping a melon and a peach together from a significant height (a second floor window is likely to prove suitable) will provide memorable proof that the mass of an object makes no difference to the rate of fall.

You should be aware of the mess which will be created by this demonstration. This can be minimised by placing a large plastic sheet on the ground. You also need to be aware of the fact that from too small a height the fruits will remain intact (no sensational explosion), while if they are dropped from too great a height air resistance might become significant and the two will not reach the ground simultaneously. The moral here is that practice makes perfect. This is certainly one of those demonstrations that makes physics fun and simply unforgettable!

You might follow this up with a discussion around interesting images, perhaps like this one:

Resources

Download a PDF of the image.

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