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Motion and Newton’s first law What is a force? Identifying forces Newton’s second law

Chapter 4 Forces and Newton’s Laws of Motion. Motion and Newton’s first law What is a force? Identifying forces Newton’s second law Free-body diagrams Newton’s third law. Topics:. Sample question:.

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Motion and Newton’s first law What is a force? Identifying forces Newton’s second law

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  1. Chapter 4 Forces and Newton’s Laws of Motion • Motion and Newton’s first law • What is a force? • Identifying forces • Newton’s second law • Free-body diagrams • Newton’s third law Topics: Sample question: These ice boats sail across the ice at great speeds. What gets the boats moving in the first place? What keeps them from going even faster? Slide 4-1

  2. Checking Understanding Which pair of forces is an action/reaction pair? • The string tension and the friction force acting on A. • The normal force on A due to B and the weight of A. • The normal force on A due to B and the weight of B. • The friction force acting on A and the friction force acting on B. Slide 5-32

  3. Answer Which pair of forces is an action/reaction pair? D. The friction force acting on A and the friction force acting on B. Slide 5-33

  4. Newton’s Zeroeth Law of Motion Objects are dumb - They have no memory of the past and cannot predict the future. Objects only know what acts directly on them in a given moment. Slide 2-34

  5. Newton's First Law of Motion Every object continues in a state of rest or a state of motion with a constant speed in a straight line unless acted on by an unbalanced net force. Or v = constant (magnitude and direction) iff net force = 0 N.

  6. What Causes Motion? In the absence of any forces acting on it, an object will continue moving forever. Motion needs no “cause.” Slide 4-8

  7. What holds it up? Forces & Kitchen Magnets Use a free body diagram to determine the force that holds up a kitchen magnet. What is the magnitude of this force?

  8. Fnet = 0 Problems Determine tension in each cable. (Hint: There is more than one way to define the system.)

  9. Fnet = 0 Problems The object hung from the cable has a weight of 25 N. Write the equation for the sum of the forces in the y-direction. What is the tension in the cable?

  10. T2 30 T1 Fnet = 0 Problems • The cable at left exerts a -30 N force. • a. Write the equation for the sum of the forces in the x-direction. What is the value of T2? • b. Write the equation for the sum of the forces in the y-direction. What is the force of gravity acting on the ball?

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