1. Moments
A moment of a force is a measure of its tendency to cause a body to rotate about a point or axis.
It is the same as torque.
A moment (M) is calculated using the formula:
Moment = Force * Distance
M = F * D
Always use the
perpendicular
distance
between the force
and the point!

2. What distance would you use here?
Moments
What distance would you use here?
Moment = Force * Distance
M = F * D
F = 20 lb
D = 2 ft
Find the moment about point P: P F
2 ft
M = F * D
M = (20 lb) * (2 ft)
M = 40 ft-lb

3. Can you visualize the result of
Moments
Moment = Force * Distance
M = F * D
Can you visualize the result of
the force acting on the beam? P F
The beam has a tendency to rotate clockwise about point P.

4. Moments P F Moment = Force * Distance M = F * D F = 20 lb D = 0.5 ft
Find the moment about point P: P F
2 ft
0.5 ft
M = F * D
M = (20 lb) * (0.5 ft)
M = 10 ft-lb

5. Can you visualize the result of
Moments
Can you visualize the result of
the force acting on the beam?
Moment = Force * Distance
M = F * D P F
The beam has a tendency to rotate clockwise about point P.

6. Moments
You have seen how a see-saw will balance on its fulcrum if equal weight is applied at both ends.
If two people of unequal weight are on the see-saw, it will rotate about its fulcrum to the side with the heavier person.
Fulcrum

7. Moments
A see-saw can also be balanced by moving the smaller person further from the fulcrum.
If a 45-pound child sat on one end 3 ft from the fulcrum, then how far from the fulcrum would a 30-pound child have to sit in order for the see-saw to be balanced?
3 ft
45 lbs
30 lbs x

8. Moments M1 = M2 45 lbs * 3 ft = 30 lbs * x 135 ft-lbs = 30 lbs * x
4.5 ft = x
3 ft
45 lbs
30 lbs x

9. Moments Typically it is assumed:
A moment with a tendency to rotate counter clockwise (CCW) is considered to be a positive moment.
A moment with a tendency to rotate clockwise (CW) is considered to be a negative moment.