Choose the bar without the end supports. Place the same two masses used above at different locations (15 kg at 1m, 10k g at 1.5 m) on the same side of the support and balance the system with a 15 kg mass on the opposite side. Record all three masses and positions. Calculate the net torque on this system about the point support and compare with the expected value. Theory:
The torque, or moment of a force, about a given axis of rotation, or pivot point, is a measure of the turning effect of the force. The torque is equal to the product of the force and its lever arm. The lever arm is the perpendicular distance from the axis of rotation to the line of action of the force. For a rigid object to be in equilibrium when non-concurrent forces are acting on it, two conditions of equilibrium must be satisfied.
The First Condition of Equilibrium states that if an object is in equilibrium, the resultant force acting on it must be zero: ΣF = 0 or ΣFx = 0 and ΣFy = 0.
The Second Condition of Equilibrium states that if an object is in equilibrium the resultant torque acting on it must be equal to zero: Στ = 0 about any axis of rotation. From vector mathematics, counterclockwise torques are positive and clockwise torques are negative.
Generally, there is one force that must be included in all calculations: the weight of the rigid object will act through its center of gravity. The center of gravity of the object is the point through which a single upward force can act to balance the gravitational force of attraction on all parts of the object, in any orientation. Alternatively, you can think of the center of gravity as the point through which the weight of the object may be considered to be acting, regardless of the orientation of the object. Experimentally, you can find the center of gravity of an object by finding the point where a single upward force balances the weight.
Procedure:
This lab will be a simulation lab. Answer the questions as you go. Go to "Balancing Act" in Phet.