 The
ability of a force to cause something to
turn
F
9/16
r = length of lever arm
Equation
 = r *F
Symbols/units
 = Torque (N*m)
r = length of lever arm (m)
F = force (N)
Torque makes it easier to turn things
Example: Normally it is difficult to loosen a nut or
bolt by hand.
 A wrench does not make you any stronger, but it
increases your turning ability.
 The farther a force is applied from the nut, the
greater the torque it produces.
 Turning
a wrench
 Levers
 Trucks
 Balances/scales
A
force of 20 N is applied to the end of a
wrench that is 0.2 m long. What is the
torque that is produced in this situation?
 = r *F


= 0.2 m * 20 N
= 4 N*m
 More
than one torque can act on an object at
one time.
 In order for the object not to spin, the
torques must be balanced

When torques are balanced they add up to zero
 Torques
can cause objects to rotate either
clockwise or counterclockwise.


Clockwise torques (+)
Counterclockwise torques (-)
clockwise
counterclockwise
3m
F1
3m
F2
F1 will cause the bar to rotate clockwise (+ torque)
F2 will cause the bar to rotate counterclockwise (- torque)
3m
10N
3m
10N
The rod will not rotate because the
torque that makes the object want to
rotate clockwise is balanced by the
torque that makes it want to rotate
counter-clockwise.
Will the following object rotate or not?
r1 = 3.2 m
F1 = 8 N
Determine the torque resulting from F1
 1 = r1F1 = 2.5 *12 = 30 Nm
Determine the torque resulting from F2
 2 = r2F2 = 3.2 * 8 = 25.6 Nm
r2 = 2.5 m
F2 = 12 N
Will the following object rotate or not?
r1 = 3.2 m
F1 = 8 N
Object won’t rotate if net torque = 0
 1 +  2 = 0?
 1 +  2 =  net
25.6 – 30 =  net
-4.4 N*m =  net
Object will rotate counterclockwise
r2 = 2.5 m
F2 = 12 N
35 N
7m
5m
175 N
6m
A man, a turtle, and a box are positioned on a giant see-saw as shown.
If the see-saw doesn’t rotate, what torque must the man produce?
Determine the torque resulting from the turtle’s weight
 T = rTFT = 5 *35 = 175 Nm
Determine the torque resulting from the box’s weight
 B = rBFB = 6 *175 = 1050 Nm
35 N
7m
5m
175 N
6m
A man, a turtle, and a box are positioned on a giant see-saw as shown.
If the see-saw doesn’t rotate, what torque must the man produce?
Net Torque = 0
 T +  B +  M =  net
-175 + 1050 -  3 = 0
875 -  3 = 0
 3 = 875 N*m
How much do
I weigh?
35 N
7m
5m
175 N
6m
A man, a turtle, and a box are positioned on a giant see-saw as shown.
If the see-saw doesn’t rotate, how much must the man weigh?
 = rF
875 = (7)F
875
F
7
F = 125 N