Consider a rigid body in equilibrium with various forces acting on it. Two conditions
must be met when it is in equilibrium: the net force must be zero and the net
torque must be zero. In this experiment you will make measurements on a rigid
system in order to verify these conditions.
The first condition, that the net force be zero, provides that the center of
mass of the body will not be accelerated. We can write this condition in terms
of a vector equation or, in the case of two-dimensions, as two scalar equations.
|
Fnet = the sum of the forces F = 0 |
|||
|
Fxnet = 0
|
Fynet = 0
|
(1)
|
Even when this condition is met the object may rotate. We thus need a second
condition, that the net torque be zero. This is a vector condition again,
but in today's lab all the torques will share the same axis so we write one
scalar equation,
|
the net torque = 0 (2) |
The directions of this one dimensional torque are generally
called clockwise (CW) and counterclockwise (CCW). We sometimes rewrite equation (2)
as
| net CW torque = 0 | net CCW torque = 0 |
(3) |
Recall that the magnitude of the torque = r F sin(q) where r is the distance from the axis of rotation to the point where the force F is applied. The angle theta is measured between the vectors r and F. For cases of static equilibrium such as today, we are free to choose any point as an axis of rotation in determining the torques.
Your Task: Find the mass of the meter stick and its uncertainty. You may not use a balance and you must use the idea of static equilibrium. There will be credit for the simplest and clearest (includes force diagram) method. When you are done, show your mass to instructor and only then compare to mass read by balance -- extra credit if they agree within your uncertainty!
This page maintained by Anne G. Young. Last modified February 13, 2004.