1. Equilibrium

2. An object is in Equilibrium if…
The net force and the net torque on it are _______
Therefore, it is not linearly or angularly _____________ or
The linear and angular momentum are __________

3. An object is in Equilibrium if…
The net force and the net torque on it are zero.
Therefore, it is not linearly or angularly accelerating or
The linear and angular momentum are constant

4. Dynamic (v=constant) Static (v=0) Unstable Stable
Types of equilibrium:
Dynamic (v=constant) Static (v=0) Unstable Stable

5. The Center of Gravity
The gravitational force the planet exerts on an object acts on ALL parts of the object.
The object behaves like the gravitational force is acting on only ONE place – the Center of Gravity
Stable objects have the cog within the perimeter of the base of the object. Objects can be more stable, or less stable, based on the width of the base.

6. Solving Equilibrium Problems:
SFx = 0
SFy = 0
SFz = 0
St = 0
(we will only deal with equilibrium in 2 dimensions)

7. Examples
P345 #9,2
Ladder example (next slide)
P347 #23,27
Assignment: Problems (NOT questions)
page #8,3,11,7,15,13,17,30,21,28

8. Ladders and Equilibrium
Ex: What is the shallowest angle a ladder can rest (against a wall) maintaining equilibrium, before the base slides? Assume the coefficient of static friction with the ground is ms and the supporting wall has no friction. The mass of the ladder is M and its length is L. What happens then, when a person climbs on and up the ladder?