Chap' 4 Force and Motion

1
Chap. 4 Force and Motion

• Force vectors

2
A Short Catalog of Forces

• Weight
• Spring Force
• Tension Force
• Normal Force
• Friction
• Drag (resistive force )
• Thrust

3
Identifying Forces and Free-body Diagram
A skier is pulled up a hill
4
An elevator accelerates upward
5
Mass

• An objective mass is a measure of the amount of
  matter it contains.
• Inertial mass

6
Newtons second law

• In the form
• Units of Force 1N 1 Kgm/s2

7
Newtons First Law

• Newtons first law Law of inertial
• An object that is at rest will remain at rest,
  or
• an object that is moving will continue to move
• in a straight line with constant velocity,
• if the net force acting on the object is zero.
• The object is at rest. This is static
  equilibrium.
• The object is moving in a straight line with
  constant velocity. This is dynamic equilibrium

8
Newtons third law

• If one object is exerting a force on a second
  object, then the second object is also exerting a
  force back on the first object. The two forces
  have exactly the same magnitude but act in
  opposite directions.

9
Free body Diagram

• Identify all forces acting on the object.
• Draw a coordinate system
• Represent the object as a dot at the origin of
  the coordinate axes.
• Draw vectors representing each of the identified
  forces
• Draw and label the net force vector Fnet