# Force exerted on the pivotal pin of an oscillating object.

1. Jan 3, 2014

### Ascendant78

If you have a rod oscillating back and forth by a frictionless pivot point near the end of one side of the rod and the only external force is gravity, how would the magnitude and direction of the force of/on that pivot point be calculated? How does it change with the oscillations?

I am having difficulty with this since torque would be ignored at that point and gravity is always pushing directly downward. I'm thinking the way to figure it out would be calculating the direction and acceleration vectors caused by the oscillations and include those forces caused by the oscillations in addition to the gravitational acceleration, but I'm not 100% sure about this one? I couldn't find a problem that looked at this aspect of oscillations anywhere in any of my physics books, so any help would be greatly appreciated.

2. Jan 3, 2014

### 256bits

There is no torque at the frictionless pin so ignoring torque is already included in the desrciption of the problem.
And you also know that from the pin being frictionless, reaction forces at the pin will have to act through the pin.

Gravity does act downwards, and then for the rod, at what point on the rod can do we usually say the force of gravity is acting..

This problem is similar to calculating the forces on a pin of a ball swinging in a circle in a vertical plane, except instead of a full circle we have part of a circle.