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Chapter M2 Section 2 Newton’s Laws of Motion Bellringer If you are sitting still in your seat on a bus that is traveling 100 km/h on a highway, is your body at rest or in motion? Explain your answer. Use a diagram if it will help make your answer clear. Record your response in your science journal. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s First Law of Motion An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force. • Newton’s first law of motion describes the motion of an object that has a net force of 0 N acting on it. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s First Law of Motion, continued • Part 1: Objects at Rest Objects at rest will stay at rest unless they are acted on by an unbalanced force. • Part 2: Objects in Motion Objects will continue to move with the same velocity unless an unbalanced force acts on them. • The image on the next slide shows how you can have fun with Newton’s first law. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s First Law of Motion, continued Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s First Law of Motion, continued • Friction and Newton’s First Law Friction between an object and the surface it is moving over is an example of an unbalanced force that stops motion. • Inertia and Newton’s First Law Newton’s first law is sometimes called the law of inertia. Inertia is the tendency of all objects to resist any change in motion. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s First Law of Motion, continued • Mass and Inertia Mass is a measure of inertia. An object that has a small mass has less inertia than an object that has a large mass. • So, changing the motion of an object that has a small mass is easier than changing the motion of an object that has a large mass. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s Second Law of Motion The acceleration of an object depends on the mass of the object and the amount of force applied. • Newton’s second law describes the motion of an object when an unbalanced force acts on the object. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s Second Law of Motion, continued • Part 1: Acceleration Depends on Mass The acceleration of an object decreases as its mass increases. Its acceleration increases as its mass decreases. • Part 2: Acceleration Depends on Force An object’s acceleration increases as the force on the object increases. The acceleration of an object is always in the same direction as the force applied. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s Second Law of Motion, continued • Expressing Newton’s Second Law Mathematically The relationship of acceleration (a) to mass (m) and force (F) can be expressed mathematically with the following equation: a = F , or F = m a m Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s Second Law of Motion, continued Click below to watch the Visual Concept. Visual Concept You may stop the video at any time by pressing the Esc key. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s Third Law of Motion Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. • Newton’s third law of motion can be simply stated as follows: All forces act in pairs. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s Third Law of Motion, continued • Force Pairs Do Not Act on the Same Object A force is always exerted by one object on another object. This rule is true for all forces, including action and reaction forces. • Action and reaction forces in a pair do not act on the same object. If they did, the net force would always be 0 N and nothing would ever move! Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s Third Law of Motion, continued • All Forces Act in Pairs—Action and Reaction Newton’s third law says that all forces act in pairs. When a force is exerted, there is always a reaction force. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 2 Newton’s Laws of Motion Newton’s Third Law of Motion, continued • The Effect of a Reaction Can Be Difficult to See When an object falls, gravity pulls the object toward Earth and pulls Earth toward the object. • You don’t notice Earth being pulled upward because the mass of Earth is much larger than the mass of the object. Thus, the acceleration of Earth is much smaller than the acceleration of the object. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 3 Momentum Bellringer Make a list of five things that have momentum and a list of five things that don’t have momentum. Explain your answer in your science journal. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 3 Momentum Momentum, Mass, and Velocity • The momentum of an object depends on the object’s mass and velocity. • Calculating Momentum The relationship of momentum (p), mass (m), and velocity (v) is shown in the equation below: p=mxv Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 3 Momentum Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 3 Momentum The Law of Conservation of Momentum • The law of conservation of momentum states that any time objects collide, the total amount of momentum stays the same. • Objects Sticking Together After two objects stick together, they move as one object. The mass of the combined objects is equal to the masses of the two objects added together. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 3 Momentum The Law of Conservation of Momentum, continued • The combined objects have a different velocity because momentum is conserved and depends on mass and velocity. • So, when the mass changes, the velocity must change, too. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 3 Momentum The Law of Conservation of Momentum, continued • Objects Bouncing Off Each Other When two objects bounce off each other, momentum is usually transferred from one object to the other. • The transfer of momentum causes the objects to move in different directions at different speeds. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter M2 Section 3 Momentum The Law of Conservation of Momentum, continued • Conservation of Momentum and Newton’s Third Law Conservation of momentum can be explained by Newton’s third law. • Because action and reaction forces are equal and opposite, momentum is neither gained or lost in a collision. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.