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