Lab - Torque

To attain equilibrium with parallel forces, two conditions must be met. 1. The sum of the

forces acting downward must equal the sum of the forces acting upward. 2. The sum of the

clockwise torques must equal the sum of the counterclockwise torques. If the forces are

acting on a rigid beam, the weight of the beam (effectively concentrated at its center of

gravity) acts as a force that must be included in the calculations of the torques.

Objective: you should understand the conditions for equilibrium of parallel forces and you

should know how to calculate any additional forces that are needed to establish equilibrium

with parallel forces.

Apparatus: meterstick, knife-edge support, set of hooked masses, meterstick clamps,

platform balance, string

Procedure: 1. Weight of meterstick as a force at its center of gravity

a. Place the meterstick on the platform balance and determine its mass.

Record this value.

b. Locate the center of gravity of the meterstick by balancing it on the broad

side of a pencil or other narrow support. Record this location in the data

table to three significant figures.

c. Support the meterstick at some location OTHER than its center of gravity

and bring it into balance by using a single mass. Record the value of the

mass and its location.

d. Conduct two more trails, with the knife-edge support at a different location

for each trial. Record all data.

2. Equilibrium of several parallel forces a. Support the meterstick at a point other than its center of gravity.

b. At the 0.10 m mark, hang a 0.200 kg mass; at the 0.20 m mark, hang a 0.100

kg mass; at the 0.90 m mark, hang a 0.020 kg mass. Determine the location

at which a 0.050 kg mass must be hung to produce equilibrium. Draw a

diagram of the set-up.

This is an example - not where you need to put the knife-edge.

Calculations: 1. Calculate the weight of the required mass and of the meterstick.

2. Find the torque arm for the required mass and calculate the torque produced by the

mass, using the location of the meterstick support as the pivot point.

3. Find the torque arm for the weight of the meterstick and calculate the force

required at the center of gravity of the meterstick to produce equilibrium.

4. Compare the force you calculated in #3 with the actual weight of the meterstick.

Find the percent difference.

Sample Analysis Table:

TRIA

L

Mass of M

eterstick (kg)

Weigh

t of mete

rstick, actual

(N)

Location of C

ente

r of Gravity

(m)

Location of m

ete

rstick

support (m)

Mass 1 �

Weigh

t 1 (N)

Location of m

ass 1 from

fulcrum (m

)

Torque

produce

d b

y mass 1

(Nm

)

Mass 2

� W

eight 2

(N)

Location of m

ass 2 from

fulcrum (m

)

Torque

produce

d b

y mass 2

(Nm

)

Mass 3

� W

eight 3

(N)

Location of m

ass 3 from

fulcrum (m

)

Torque

produce

d b

y mass 3

(Nm

)

Mass 3

� W

eight 4

(N)

Location of m

ass 4 from

fulcrum (m

)

Torque

produce

d b

y mass 4

(Nm

)

Torque

arm for w

eigh

t of

mete

rstick (Nm

)

Torque

produce

d b

y require

d

mass (N

m)

Weigh

t of mete

rstick,

expe

rimental – d

ue to calc’n

of torque = 0

Nm

(N)

Perce

nt Diffe

rence

(%)

1

2

3

Questions: 1. Does the accuracy of your results in finding the weight of the meterstick improve

when the knife-edge support is placed farther from the center of gravity? Explain.

2. Under what conditions would it be impossible to produce equilibrium in this

experiment with the addition of a single mass?