Air resistance and drawing free body diagrams
Worksheets and lesson ideas to challenge students aged 11 to 16 to think hard about air resistance and free body diagrams (GCSE and Key Stage 3)
A feather and a bowling ball are dropped at the same time. Which hits the ground first? This question requires really profound thinking, and challenges students’ prior conceptions. Intuitively students will think that the bowling ball will hit the ground first because it is heavier or because it experiences less air resistance than the feather – both are wrong explanations. What happens then if we remove all the air particles? Here, Professor Brian Cox drops a feather and a bowling ball in the world’s largest vacuum chamber so let’s see what happens.
Demonstrating the effects of air resistance
Take a piece of a4 paper and a cricket ball. Ask students which one will hit the ground first if dropped. Ask them to explain their reasoning. Now drop both objects at the same height. They will observe the ball hitting the ground first due to the effects of air resistance acting on the paper (note both objects will experience air resistance). Now repeat the demonstration, but this time screw the paper into a ball that is roughly the same shape as the cricket ball. Both objects should hit the ground at the same time. You could then get students to explain this demonstration using the model below. Thanks to Alom Shaha for reminding me about this demonstration in his book Why Don’t Things Fall Up?
Modelling air resistance
Key Stage 3/GCSE activity on modelling air resistance. Ping pong balls and juggling balls are used to model air resistance and get students feeling the force. Students discuss a series of questions about the model and air resistance. This demonstration should only be used with a class that you are confident with! (PDF)
Drawing free body diagrams
GSSE worksheet on drawing free body diagrams. Students draw free body diagrams for some challenging situations. They can use the worksheet to check their answer. More information on drawing free body diagrams can be found here. (PDF)
This link to the forces dance mat is a great way to assess whether students understand simple force diagrams.