Pre-Engineering Physics Name__________________________

Torque and Equilibrium Lab Class/period_____________________

Background: Torque and Equilibrium-The two conditions for an object to be in equilibrium are (1) zero net force and (2) zero net torque on the object. This experiment will deal with rotational equilibrium and torques. Torque is a measure of a force's tendency to produce rotation and can be defined by

Torque = Force x Lever arm

where the lever arm is the perpendicular distance from the axis of rotation to the line of action of the force. This is illustrated in the diagram below for a bicycle pedal; at different points in the pedaling motion the force of the rider's foot is more effective in producing rotation because the lever arm is longer.

When more than one torque acts to produce rotation about an axis it is often convenient to divide them into clockwise and counterclockwise torques, and the condition for rotational equilibrium is then

*Sum of clockwise torques = Sum of counterclockwise torques

(or the sum of all total torques = zero)

Problem 1:

I. Balance multiple torques using the following equipment:

Meter stick

Knife-edge supports

Mass hangers

Assorted gram masses; known and 1 unknown mass

Triple-beam balance

1. Balance the meter stick in a horizontal position on its knife-edge support with no weights attached. Record the point on the stick at which it balances.

2. Suspend three masses from the meter stick as indicated in the sketch and move them until you balance the meter stick. Record the mass values and their positions.

3. Determine the lever arm associated with each mass and record the values in the data table below. Compute the mass times the lever arm for each mass. (The torque, strictly speaking, is the weight times the lever arm. But the mass times the lever arm differs only by the constant g, the acceleration of gravity, so for the balance condition it serves the same purpose.)

4. Compare the clockwise and counterclockwise torques.

Sum up the CCW torque=

Sum up the CW torque=

Now combine the above sums and show calculation of theoretical value of torque sums here. Set equal to zero.

St=

Data: Pivot point on meter stick _____________

Problem 2: Determination of unknown mass

1. After removing the other masses, suspend the supplied unknown mass from a convenient point on one side of the meter stick. Use one of your known masses to produce rotational equilibrium. Perform the calculations to find the unknown mass. Then find the mass of the unknown on the triple beam balance and compare your results.

Data:

Unknown mass (calculated; show calculations below) _____________

Unknown mass (from triple beam balance) ______________

%difference _________________

(%difference=(difference between the two masses/average of two masses)X100

Problem 3: Determination of meter stick mass

1. Move the meter stick in its support so that the new pivot point is 10 cm away from its balance point (either way). Restore balance by hanging a known mass from one side of the meter stick. Using the equilibrium condition, determine the meter stick’s mass and check your result by massing the stick on the triple beam balance.

Data:

Meter stick mass calculated ________________

Show calculations here.

triple beam balance mass of meter stick_______________

%difference _________________

(%difference=(difference between the two masses/average of two masses)X100