Lesson 2 of 3
Moments and Torque
Learn how forces create rotation and how to calculate moments about a point.
What is a moment?
A moment (or torque) is the rotational effect of a force about a point. It depends on both the force and the perpendicular distance from the point to the line of action:
M = F · d
Where M is the moment, F is the force, and d is the perpendicular distance
(the "moment arm").
Sign convention
Choose a consistent convention - commonly counterclockwise moments are positive, clockwise are negative. Stick with it throughout a problem.
Why moment arm matters
A small force with a long moment arm can produce a large moment. This is why a wrench handle is long, and why door handles are placed far from the hinge.
Example
A 50 N force applied 0.3 m from a pivot:
M = 50 N · 0.3 m = 15 N·m
Moments are the key to analyzing beams, levers, and any structure that resists rotation.