# Uniform linear, circular and rotational motion

In uniform linear motion, an object moves at a constant speed v0. And as long as no acceleration is applied onto the object, it will continue move at the same speed and direction forever.

For uniform circular motion to happen, an object must move at a constant speed v0 with a constant perpendicular acceleration of magnitude v2/r. This perpendicular acceleration always points toward the center of circular path. However, something must continuously provide the centripetal force for the perpendicular acceleration otherwise the object will become a linear motion instead.

What about rotational motion? I know that just line linear motion, if an object is spinning at a constant angular speed w0; it will keep spinning at that constant speed forever if no angular acceleration is applied. However, centrifugal force must be present for rotational objects. How can the object provide itself centrifugal force with no external influence?

Disconnected
Gold Member
The object can certainly provide it's own centripetal force.

Think of a 1m rigid rod in space. if you push the ends in opposite directions, it will spin and keep spinning, right?

Now imagine that the very centre of the rod is gone, so it's just two 0.5m rods touching. If you push on these in just the same way as the original rod, they will just float apart, right?

The bonds in the rod provide tension, and this tension is the centripetal force that stops that ends of the rod floating apart and therefor causes them to follow rotational motion.