# Non-uniform vertical circular motion

A roller coaster in a vertical circle will have a velocity change. This change in velocity will change the radial acceleration. My text book states that

“the car is changing only direction, not speed, at the very top and very bottom locations so at these points the acceleration is purely centripetal so Newton’s Second Law applies”.

Why this is only relevant at the top and bottom of the circle?

• Odd that the quote implies Newton's Second Law only applies at those two points. – M. Enns Jan 8 '17 at 4:50