Turning Needs a Force

Lesson 9 of 11 · 7 min · Free, no account needed

What you will learn

To move in a circle, something must keep pulling or pushing the object toward the centre: the centripetal force.
It is not a new kind of force. Tension, friction or gravity does the job. There is no force pushing outward.
Faster or tighter turns need more inward force: it grows with the speed squared and with a smaller radius.

In a sharp turn you slide toward the car door. Is something pushing you outward?
Simpler case first: a ball whirls on a string. Draw its path if the string snaps right now.
Whirl it and let go. Try different moments.
How hard must the string pull? Change the speed and the radius.
The inward force has a name.
Centripetal force: the net force toward the centre that keeps something on a circle. Without it, the object goes straight on.
It is a job, not a new force: tension does it for the ball, friction for a car, gravity for the Moon. In the car, you slide toward the door because the car turns and you keep going straight.
It needs to be bigger for faster or tighter turns: F = m v² ÷ r. Simplified model: steady speed around a perfect circle.
Game: drift. Three corners, total time 9 s or less.
Pick the entry speed for each corner. Too fast and the tyres cannot hold you; too slow costs time.
Three things going round. For each one, tap what supplies the inward force.
Code: build the loop that keeps a satellite on a circle. Choose the two lines that change its velocity.
Every frame, a small push toward the planet at (0, 0) is added to the velocity.
A car takes a left turn at a steady speed. Show the net force on it.
Your three corners against the grip limit. Press Play.

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