# Tangential Acceleration

## Homework Statement

A uniform rod of length 1.4 m is attached to a frictionless pivot at one end. It is released from rest from an angle θ = 23° above the horizontal. Find the magnitude of the initial acceleration of the rod's CM.

At = alpha * r

## The Attempt at a Solution

I am reviewing old homework problems for my test tomorrow so I just have a few questions....
What is CM?
Also is At known as initial acceleration not Ac?

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Hootenanny
Staff Emeritus
Gold Member
CM stands for 'Centre of Mass' and since the rod is uniform one can work out the acceleration by looking at the net force acting on the rod's CM.

So is tangential acceleration known as initial acceleration not centripetal acceleration?

Hootenanny
Staff Emeritus
Gold Member
So is tangential acceleration known as initial acceleration not centripetal acceleration?
No, the tangential acceleration is orthogonal to the centripetal acceleration by definition.

Doc Al
Mentor
In general, the acceleration of the center of mass (or any other point on the object) will have two components: centripetal and tangential. But what does the centripetal component depend upon?

centripetal depends on the forces acting on the object I think

Doc Al
Mentor
centripetal depends on the forces acting on the object I think
Well, sure. But what I was going for was that centripetal acceleration depends on the speed of rotation. And immediately after this rod is released from rest, what is its initial rotational speed?

0 rad/s^2, I guess I am don't understand the difference between at and ac and when to use which one.

Doc Al
Mentor
The tangential acceleration (which is proportional to the angular acceleration) has to do with the rate at which the angular speed changes. If the rate of rotation is constant, the tangential acceleration is zero.

But as long as the rod is rotating, the center of mass will have some centripetal acceleration.