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Transcript
Newton’s Laws of Cool! Motion I like to sing the abc’s! Ouch! What’s with the apple dude? INERTIA Tendency of objects to resist changes in motion Larger mass = more resistance to change First Law of Motion: the Law of Inertia In his own words: An object at rest will remain at rest and an object in motion will remain in motion at constant velocity unless acted upon by an unbalanced force. Second Law of Motion: The law of Acceleration 2nd Law of Motion Force = Mass x Acceleration F = m x a or a = F/m An unbalanced force will cause an object to accelerate Acceleration is related to the amount of force and mass vs. Third Law of Motion: The law of Interaction rd 3 Law of Motion For every action force , there is an equal and opposite reaction force -Forces occur in equal and opposite pairs The following slides are examples of the laws Sled dogs join together to exert a force to overcome the inertia of the sled. What will cause the sled to stop? NEWTON'S FIRST LAW When the car hits the cement road divider it is stopped (an outside force stops it from moving). The crash dummy, however, is not so lucky. Since he is not wearing a seat belt, and is not connected to the car, he will continue to move at 60 mph. This means he will go flying out through the front windshield (don't try this at home). The dummy will fly through the air until he hits the ground. This is because the earth's gravity stopped him from moving any further (his trajectory is a combination of the downward force of gravity, and the horizontal force of the moving car). If this collision had happened in zero-g, in a vacuum, the dummy theoretically would keep on hurtling away from the car at 60 mph Why must he exert more energy to start running from a stopped position than to continue running once he has begun? BOB's van, which weighs 2,000 kg, is out of gas. BOB is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. Using Newton's 2nd Law, you can compute how much force BOB is applying to the car. Although the ball has small mass, its acceleration off the racket is great. Why? Unit of Force Mass kilograms Acceleration m/sec/sec force newtons(N) 1N = 1 kg x 1 m/sec/sec Why do huge trucks need to exert great force to accelerate than small vehicles? How much force is needed to accelerate a 1400 kg car 2 m/sec/sec? Step 1: F = MA Step 2: F = 1400 kg x 2 m/sec/sec Step 3: F = 2800 kg-m/sec/sec or 2800 N How much force is needed to accelerate a 66-kg skier 1m/sec/sec? F= 66 newtons What is the force on a 1000-kg elevator that is falling freely at 9.8 m/sec/sec? F= 9800 newtons Here we see BOB punching Mike in the face. Here we see Space Man Spiff's rocket ship. BOB (who isn't very bright) is tired of pushing his van to the gas station. He gets an idea -- "Hey! I go much faster when I am rollerblading than when I am walking. Why don't I wear my rollerblades!" So BOB gets his roller blades from the back of his van, and starts pushing. Since every action has an equal and opposite reaction, when BOB pushes the van, the van pushes BOB. BOB weighs 50 kg, and the van weighs 2,000 kg. Thanks to the Second Law, you can compute how much BOB and the van will move after 1 second (hint: use A=f/m). Ooops…What happened here? How does the third law of motion explain the movement of a water sprinkler?