Why does a ball curve?
A plain-English answer for grown-ups of kids aged 6–9, taken from the Yufena lesson that explores this question.
This is a members' lesson. Four other lessons are free to try.
The answer, for parents
Short answer: A spinning ball makes the air push harder on one side, so the ball curves. This is the Magnus effect.
How you kick the ball matters. If you hit the side of the ball, it starts to spin. Air is all around us, even if we cannot see it. A flying ball pushes through the air. The air flows around it on every side.
A spinning ball drags a thin layer of air with it. On one side, this helps the air flow past. On the other side, it bumps into the air. So the air pushes harder on that side! Scientists call this push pressure. The ball moves towards the side with less push. So it curves through the air! This is called the Magnus effect.
In the lesson, your child puts this cause-and-effect chain in order: Kick the side of the ball → The ball spins → Spin changes the air on each side → One side gets pushed harder → The ball curves.
What if the ball doesn't spin? It flies straighter. Sometimes it wobbles and dips in a funny way!
Where else do spinning balls curve? Table tennis and tennis topspin shots dip down fast. Golf balls use backspin to fly further.
Try it with your child
Let's test spin! Go outside or into a corridor. Throw a light ball with no spin. Watch how it flies. Now flick your fingers as you throw, so it spins. Does it curve? Try spinning it the other way too!
Safety: Safety first: use a light ball and keep away from windows.
Explore it together in the full lesson
Guess, find clues, build the chain and try the experiment. Read it together.