7.4 static rigid bodies, 7.5 dynamics and inclined planes, 7.6 connected particles

If you need to consider the rotational forces acting on an object, how can you model it?

As a rigid body

What does it mean for a rigid body in static equilibrium?

• the body is stationary

• the resultant force in any direction is zero

• the resultant moment is zero

You will sometimes need to consider the moments acting in the body and the resultant force acting on the body separately

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Example 7

Example 8

Example 9

Why is the reaction not a normal reaction here?

• Because the floor is rough and therefore the reaction has a frictional component as well as a normal component

• The reaction of the floor on the rod will be the resultant of the two components

When a particle is moving along a rough plane, what is the force of friction?

• the force of friction is equal to µR

• Acts so as to oppose the direction of motion

Example 10a

Example 10b

Example 11

When do you need to be able to solve problems about connected particles?

• connected particles on inclined

• connected particles on rough surfaces

When is the only time connected particles aren’t considered separately?

When connected particles are moving in the same direction

Example 12 pt 1

Example 12 pt 2

Example 13ai

Example 13aii, b, c