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Transcript
Forces 9.3 Table of Contents Newton’s Laws of Motion Essential Question: How Do Objects React to Forces? What is Newton’s First Law of Motion? What is Newton’s Second Law of Motion What is Newton’s Third Law of Motion Vocabulary Inertia-resistance to change in motion Inertia movie http://www.gamequarium.org/cgi-bin/search/linfo.cgi?id=6936 Game on the moon http://teacher.scholastic.com/activities/explorations/space/level1/interactive.htm Games online http://www.quia.com/mc/1270039.html http://www.quia.com/mc/1270039.html Newton’s Laws of Motion First Law An object in motion will stay in motion, and an object at rest will stay at rest unless an unbalanced object acts on it. Second Law An object that has an unbalanced force acting on it will accelerate in the direction of that force (an object’s acceleration depends on its mass and on the net force acting on it) Third Law Forces always occur in equal and opposite pairs (one object exerts (applies) force on another object, then the second exerts equal strength in the opposite direction on the object) Action pairs= Action force & Reaction force Online StudyJam 1st Laws of Motion Newton’s First Law of Motion pg. 340 If an object is not moving, it will not start moving until a force acts on it. If an object is moving, it will continue at a constant velocity until a force acts to change its speed or direction. Newton’s 1st law of motion states that an object at rest will remain at rest unless acted upon by an unbalanced force. An object moving at a constant velocity will continue moving at a constant velocity unless acted upon by an unbalanced force. 1st Law of Motion Cartoon Newton’s First Law of Motion Pg. 341 Inertia-resistance to change in motion •Inertia depends on Mass •Some objects have more inertia than others The greater the mass of an object greater inertia (resistance to change motion) The greater the force required to change its motions Fig. 1 Online StudyJam 2nd Laws of Motion Newton’s Second Law of Motion Pg. 342 Brainpop r. pg. Second Law An object that has an unbalanced force acting on it will accelerate in the direction of that force (an object’s acceleration depends on its mass and on the net force acting on it) 2nd Law of Motion If two dogs are on each side, then the total force pulling to the left (200 N) balances the total force pulling to the right (200 N). That means the net force on the sled is zero, so the sled doesn’t move. Pg. 342 Acceleration Equation: Acceleration = Net Force Mass Net Force Equation: Net Force = Mass X Acceleration Fig. 2 pg. 342 Newton’s Laws of Motion Newton’s Second Law Suppose that four dogs pull a sled carrying two people. How can the pictures be completed to represent answers to the two different questions? DO THE MATH Pg. 343 Every year in cities around the world, teams create cars, push them across platforms, and hope they will fly. Unfortunately, the cars always end up accelerating down into the water. 1. Calculate- If a 100-N net force acts on a 50 kg car, what will the acceleration of the car be?_______________________ 2. Calculate- After the car leaves the platform, gravity causes it to accelerate downward at a rate of 9.8 m/s2. What is the gravitational force on the car? ________________________________________________ Assess your understanding Pg. 343 S.I. Unit for Acceleration = M/s2 S. I Unit for Mass= kg S.I. Unit for Force= N Newton’s 2nd Law of Motion- Force is measured in kilograms times meters per second per second (kg•m/s²)= Newton force is measured This unit is also called the newton (N), which is the SI unit of force. One Newton is the force required to give a 1kg mass an acceleration of 1 m/s2 Online StudyJam 3rd Laws of Motion 3rd Law of Motion pg. 344 Third Law Forces always occur in equal and opposite pairs (one object exerts (applies) force on another object, then the second exerts equal strength in the opposite direction on the object) Action pairs= Action force & Reaction force . Another way to state Newton’s third law is that for every action there is an equal but opposite reaction. Action and reaction forces do not necessarily cancel out because they may act on different objects 3rd Law of Motion Sir Isaac Newton's Third Law of motion, which states that for every action, there is an opposite reaction. The classic example is air rushing out of a balloon (action) and the balloon streaking ahead (reaction). r. pg. 344 ? DID YOU KNOW Pg. 345 Newton’s 3rd law of motion explains why rockets accelerate in space, even though there is no water or air to push off of. Inside rockets, gas is produced. When the rockets push that gas backward out of the rocket, a reaction force occurs that pushes the rocket forward. Newton’s Laws of Motion pg. 345 Action-Reaction Forces How can the illustration of the dogs be completed to represent Newton's Third Law of Motion? Newton’s Laws of Motion pg. 346-47 What Makes a Bug Go Splat? Splat! A bug has just flown into the windshield of an oncoming car. The car must have hit the bug much harder than the bug hit the car, right?
