This week, Year 7 conducted an experiment in physics that thoroughly challenged their previous understanding of forces.
Children were asked to predict which item would fall fastest; a very heavy shot put or a lighter foam ball? Both balls were a similar size but very different in their weight. Many children predicted that the shot put would fall much faster as it so much heavier.
To their surprise, both balls hit the floor at almost exactly the same time from a 2m height. So what was going on here?! Why was there so little difference given the great difference in the weight of the objects?
In order to explore this further, we conducted tests with a range of balls; light and heavy, small and large. The results were dramatic in many cases.
The class learned to consider the frictional force of air resistance in order to explain their results. Here were some of their thoughts:
- “Air resistance increases as an object accelerates towards the floor.”
- “The weight of the object doesn’t change, but the amount of air resistance does.”
- “Do large objects create more air resistance?”
- “Small objects create less air resistance because they can cut through the air.”
- “Lighter objects reach their top speed quickly but heavy objects keep getting faster for longer.”
- “Does a rough object create more air resistance?”
- “Do the holes in a wiffle ball create more or less air resistance?”
- “The air particles hit the ball and stop it from accelerating forever.”
- “Small, heavy objects are not affected by air resistance as quickly as bigger or lighter ones.”
With their experiments completed, we sat down to make predictions on which ball would fall the fastest. Want to play the game with us?! Can you predict which ball will hit the ground first? Each group introduced the balls they used:
Test 1: This one should be easy! A small foam ball vs the shot put:
Easy win for the shot put! The foam ball reached its maximum speed very quickly, but the shot put continued to accelerate, overtaking the foam ball by a distance.
Test 2: Big, bouncy kickball vs little wiffle ball. Tricky one this…
Looks like a draw – students decided that we would need to drop these from a much greater height to test this for sure!
Test 3: Hard hockey ball vs foam ball:
Great video, this one! Showing the longer acceleration of the heavier, hard hockey ball over the foam ball.
Test 4: Getting tricky again now! A small dice vs large, much heavier kickball.
Big win for the dice! This video proves 100% that the heavier object doesn’t always fall faster.
Test 5: Hard to split these two – slightly heavier, spiky ball vs smooth mini basketball. Both were approximately the same size, but there was a noticeable difference in weight. The spiky surface caused a lot of discussion – would it cause lots of air resistance?! Place your bets…
Nope – in this case, the greater weight was the deciding factor.
Test 6: And, finally, small wooden ball vs larger plastic ball…
Hard to judge this…the class decided that the wooden ball had been released slightly earlier, so judged this as a draw. Everyone agreed that this deserved a re-test as the results were not reliable.
So, all in all, pupils learned that the heavier object did not always fall faster. The relative impact of air resistance, and how we can calculate it, was of greater interest to the children in the end. We’d better dust off our calculators…
Finally, to truly recognise the dramatic impact of air resistance, we watched these amazing videos – check them out!
https://www.youtube.com/watch?v=E43-CfukEgs
https://www.youtube.com/watch?v=KDp1tiUsZw8
We hope you enjoyed a little physics with us today!