1. Chapter 4: Forces and the Laws of Motion
4.1 Changes in motion

2. Force Forces cause changes in velocity
We usually imagine a force as a push or a pull on an object.
Force – the cause of an acceleration, or the change in an object’s velocity.
What are three ways to change a velocity?

4. The units for force
Important equivalents: 1 N = lb

5. Forces can act through contact or at a distance.
Contact force – force that arises from the physical contact of two objects.
What are some examples?
Field force – force that can exist between objects, even in the absence of physical contact between the objects.
Gravitational field force between any two masses
Electrical field force between any two charges particles.

8. Force Diagrams Force is a vector
The effect of a force on an object depends on the magnitude and direction of the force.
Force diagram – a diagram of the objects involved in a situation as well as the forces acting on the objects.

9. A free-body diagram helps analyze a situation.
Shows only the object of interest and the forces acting on it.

10. A free-body diagram in practice:
Draw a simple shape to represent the object
Then draw all the identified forces coming out of the object, each indicating both magnitude and direction.