1. Chapter 4
Forces

2. What is a force?
Push or a pull
Can push or pull by with or without touching
Field forces: no contact required
Contact forces: objects must touch to push or pull
Vectors, forces have both magnitude and direction
Forces can cause acceleration
Acceleration is change in
Direction
Magnitude
SI units for force: newtons, N or kg m/s2

3. force demonstration

5. Newton’s Laws of Motion
Newton’s first law
Inertia
Objects remain at rest or move at constant velocity unless acted upon by a net, unbalanced force
Use free body diagrams to determine if there is a net force.
Free body diagram
Illustrates all the forces that are acting upon an object
Show relative size and direction of each force

6. Newton’s Laws of Motion
Newton’s Second Law
Acceleration
The acceleration of an object is directly proportional to the net force on the object and inversely proportional to the mass of the object
Net F = m a
acceleration demonstration

7. Newton’s Laws of Motion
Newton’s 3rd Law
Action-reaction

8. Newton’s Laws of Motion
Newton’s 3rd Law
Action-reaction
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
Fof 1 on 2 = -Fof 2 on 1
Action-reaction demonstration

9. Newton’s Laws of Motion
Newton’s 3rd Law
Fof 1 on 2 = -Fof 2 on 1
more action-reaction