# A stick falls.

1. Feb 3, 2014

### jordanhuh

Mod note: deleted image that was way too large.
1. The problem statement, all variables and given/known data
I want to know the time flowed while the stick falls.

gravity = g
density of the stick is same so it's center of mass is l/2.
what is the T?

2. Relevant equations

3. The attempt at a solution
failed to do torque.

Last edited by a moderator: Feb 3, 2014
2. Feb 3, 2014

### Simon Bridge

You mean - "how long does it take for the stick to fall?"
Is the point of contact a fixed pivot?

... then learn.
The subject requires an actual physics lesson - there is no shortcut - lessons are expensive for a reason.

You need to draw the forces into the diagram.
At the center of mass, gravity creates a torque.

Torque is the perpendicular component of the force times the distance.
In your case, the torque will depend on the angle.

The equation to solve is $\sum\tau = I\ddot\theta$ ... so you need to know about angular momentum as well. For the stick, pivoted about one end, $I=mL^2/3$ - where L is the length of the stick.

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