1. Chapter 5: Force and Motion – I
Reading assignment: Chapter 6
Homework : (due Wednesday, Sept. 14, 2005)
Chapter 6: Q18, 8, 20, 31, 38, 69
In this chapter we will learn about the relationship between the force exerted on an object and the acceleration of the object.
Forces
Newton’s three laws.

2. Newton’s third law
“For every action there is an __________ and __________ reaction.”
If two objects interact, the force F12 exerted by object 1 on object 2 is equal in magnitude and opposite in direction to the force F21 exerted by object 2 on object 1:
Action and reaction forces always act on ____________ objects.

3. Where is the action and reaction force?
Action-reaction pairs act on DIFFERENT objects
n … normal force
When a body presses against a surface, the surface pushes on the body with a normal force n, that is __________________________ to the surface.

4. Black board example 5.2 Conceptual example:
A large man and a small boy stand facing each other on frictionless ice. They put their hands together and push against each other so that they move apart.
Who moves away with the higher speed
Who moves farther while their hands are in contact?

5. Black board:
Analyzing forces
Free _________ diagram
Tension in a rope = magnitude of the force that the _________ exerts on object.

6. Black board example 5.3
A traffic light weighing 125 N hangs from a cable tied to two other cables fastened to a support as shown in the figure.
Find the tension in the three cables.