# PHY110 CHAPTER 5.ppt - PHY110 CHAPTER 5 NEWTONu2019S LAW...

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CHAPTER 5: NEWTON’S LAW OF MOTION PHY110 1
Lecture Outline TOPIC 5.1: NEWTON’S LAW Newton’s 1 st Law – Inertia Newton’s 2 nd Law Newton’s 3 rd Law 2
3 Newtons Law Isaac Newton (1642 – 1727). Newtonian mechanics – classical. Cannot apply for speeds close to speed of light – Quantum mechanics / Einstein theory of relativity.
Newton’s 1 st Law is often called: The Law of Inertia 4 Newton’s First Law If F = 0, then v = 0 ms -1 or a = 0 ms -2 [NHB] An object will remains at rest or at constant velocity along a straight line until a force act on it.
Inertia and Mass Inertia is a tendency for an object to continue its motion in the absence of a force. Mass is a quantitative measure of inertia. Mass is not weight. Mass is a property of an object. Weight is the force exerted on that object by gravity (gravitational force). SI unit of inertia and mass is kilogram (kg) 5
Explanation: The inertia of the coin resists the change of its initial state, which is stationary. As a result, the coin does not move with the cardboard and falls into the glass because of gravity. 6 Inertia and Mass When a cardboard is jerked quickly, the coin will fall into the glass. Situation involving Inertia 1 – Jerking a card
7 Explanation: Inertia tries to oppose the change to the stationary situation, that is, when a book is pulled out, the book on the top do not follow suit. Inertia and Mass When a book is pulled out, the book on the top will fall downwards. Situation involving Inertia 2 – Pulling a book
8 Relationship between Inertia and Mass Larger mass – greater inertia Explanation: Object with more mass offers a greater resistance to change from its state of motion. Object with larger mass has larger inertia to resist the attempt to change the state of motion. Bucket filled with sand is more difficult to be moved . It’s also more difficult to be stopped from swinging.
9 Relationship between Inertia and Mass An empty cart is easier to be moved compare with a cart full with load. This is because a cart with larger mass has larger inertia to resist the attempt to change the state of motion .
10 The law of inertia says that an object’s velocity will change (eg.: it will accelerate) if a nonzero force is applied to it. Therefore, force causes acceleration. Newton’s 2 nd Law picks up on this theme & tells us, quantitatively, how the acceleration relates to the net force. Relationship between 1 st and 2 nd Newton’s Law What happen to the passengers in the bus when the driver suddenly had an emergency brake?
Newton’s 2 nd Law is the relation between acceleration and force . Acceleration is proportional to force while inversely proportional to mass. 11 Newton’s Second Law m F a net a m F net x x a m F y y a m F
Newton’s 3 rd Law:
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