1. Torque, & Rotational Equilibrium
Chapter 8, Sections 1 & 2 Pg

2. Torque
Torque (τ): A quantity that measures the ability of a force to rotate an object around an axis.
lever arm (d) F +
axis of rotation or F -

3. Torque is measured in N•m
The applied force acting on an object to cause rotation can be either:
1. Perpendicular
τ = Fd
2. At an angle
τ = Fd(sin θ)

4. Sample Problem
What is the magnitude of torque produced by a 3.0 N force applied to a door at a perpendicular distance of 0.25 m from the hinge?
τ = Fd
τ = 3.0 N (0.25 m)
3.0 N
(Top View)
τ = 0.75 N•m

5. Objects rotating about an axis experience a resistance in rotational motion (moment of inertia)
???
Unless a net torque is applied to a rotating object, it will not rotate!!!

6. Rotational Equilibrium
Occurs when the net torque applied to an object’s center of mass is zero. d1
Center of mass W1 W2 d2 τ1 τ2 =

7. Sample Problem τ1 = τ2 d1 = 0.75 m 200 N W2 = ? d2 = 0.5 m
W1 • d1 = W2 • d2
200 N • 0.75 m = W2 • 0.5 m
W2 = 300 N