← Centripetal force

More speed, more force needed

The same car rounds the same circular bend twice, at a steady 11 m/s and then a steady 16 m/s. Same bend, same car, one thing changed: the speed.

Which run needs the larger centripetal force?

You have seen that a greater speed on the same circle means a greater centripetal acceleration.

Giving the same mass a greater acceleration takes a larger net force.

So the 16 m/s run needs a larger centripetal force than the 11 m/s run.

steady 11 m/sthe same carsteady 16 m/sthe same car
Same bend, same car. The faster run needs the larger centripetal force.
Hold mass and radius fixed: more speed, more force needed; less speed, less force needed.
steady 11 m/sthe same carsteady 16 m/sthe same carspeed down
Read it the other way: less speed, less force needed.

A later lesson gives the exact relationship. Here, the direction of the change is the point.

Speed axis, mass and radius fixedchangecentripetal force neededspeed up, same mass and radiusgets biggerspeed down, same mass and radiusgets smaller
One axis at a time: the speed, with mass and radius held fixed.

A subway train takes the same curved section of track at a steady 12 m/s, then at a steady 17 m/s. Compare the centripetal force needed on the faster run.

A go-kart laps a circular loop at a steady speed, then repeats the loop at a lower steady speed. Compare the centripetal force needed on the slower lap.

A motorcycle rounds the same flat curve at a steady 9 m/s, then at a steady 14 m/s. Compare the centripetal forces needed on the two runs.

The curve and the mass are the same on both runs. Only the speed differs.

A greater speed on the same circle needs a greater centripetal acceleration, and the same mass at a greater acceleration takes a larger force.

The 14 m/s run needs the larger centripetal force.

Luca says: the same sports car rounding the same curve needs a larger centripetal force at 25 m/s than at 20 m/s. Is he correct?

Your turn

A city bus takes the same traffic circle at a steady 7 m/s on a quiet day and at a steady 10 m/s when running late. Which statement is correct?

Four identical vans round the same flat curve at steady speeds of 8 m/s, 10 m/s, 13 m/s, and 15 m/s. Which van needs the greatest centripetal force?

Two identical trucks round the same curve at steady speeds. The red truck needs a larger centripetal force than the white truck. Which statement follows?