Chapter_4 physics slides

Chapter_4 physics slides - Chapter 4 Units of Chapter 4...

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Chapter 4 Dynamics: Newton’s Laws of Motion 1 Units of Chapter 4 9 Force 9 Newton’s First Law of Motion 9 Mass 9 Newton’s Second Law of Motion 9 Newton’s Third Law of Motion 9 Weight—the Force of Gravity 9 Free-Body Diagrams 9 Problem Solving—A General Approach 2 4-1 Force A force is a push or pull . An object at rest needs a force to get it moving ; a moving object needs a force to change its velocity . 3 4-1 Force Force is a vector , having both magnitude and direction . The magnitude of a force can be measured using a spring scale. 4
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4-1 Force Identifying forces… (a) Non-contact forces … arise between two objects even though they do not touch each other. Gravity . Weight – Electromagnetic forces. – Nuclear interaction forces. (b) Contact forces … arise when two objects touch each other. Push or pull . Tension … act along the length of a rope. Normal forces … are perpendicular to a surface. Frictional forces … are parallel to a surface. 5 6 Isaac Newton ( 1642 – 1727) 7 4-2 Newton’s First Law of Motion This is Newton’s first law , which is often called the law of inertia : Every object continues in its state of rest, or of uniform velocity in a straight line, as long as no net force acts on it. F represents the force applied by the person and F fr represents the force of friction. 8
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4-2 Newton’s First Law of Motion Conceptual Example 4-1 : Newton’s first law. A school bus comes to a sudden stop, and all of the backpacks on the floor start to slide forward. What force causes them to do that? Answer: No force ; the backpacks continue moving until stopped by friction or collision. 9 4-3 Mass Mass is the measure of inertia of an object, sometimes understood as the quantity of matter in the object. In the SI system, mass is measured in kilograms . Mass is not weight . Mass is a property of an object . Weight is the force exerted on that object by gravity. If you go to the Moon, whose gravitational acceleration is about 1/6 g , you will weigh much less. Your mass, however, will be the same. 10 4-4 Newton’s Second Law of Motion Newton’s second law is the relation between acceleration and force. Acceleration is proportional to force and inversely proportional to mass. It takes a force to change either the direction or the speed of an object. More force means more acceleration; the same force exerted on a more massive object will yield less acceleration . The bobsled accelerates because the team exerts a force. 11 4-4 Newton’s Second Law of Motion Force is a vector, so is true along each coordinate axis. The unit of force in the SI system is the newton (N) . 12
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4-5 Newton’s Third Law of Motion Any time a force is exerted on an object, that force is caused by another object. Newton’s third law: Whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first.
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This note was uploaded on 02/22/2011 for the course PHYS 111 taught by Professor Madrid during the Spring '08 term at Ohio State.

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Chapter_4 physics slides - Chapter 4 Units of Chapter 4...

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