NEWTON’S FIRST LAW A BODY AT REST REMAINS AT REST AND A BODY IN MOTION REMAINS IN UNIFORM MOTION IN A STRAIGHT LINE UNLESS ACTED ON BY AN EXTERNAL UNBALANCED FORCE
Newton’s First Law Explained Experience tells us that a stationary object remains at rest unless acted on by some outside force. We know that forces are necessary to cause anything to move if it is originally at rest.
<ul><li>Less obvious is the fact that an object in motion will continue in motion until an outside force changes the motion. For example, a rolling ball slows down until it stops rolling because of its interaction with the floor, called friction, between the floor and the ball. The ball will roll longer and farther in a smooth surface than in a rough one. This leads to the idea that if the surface is frictionless the ball will move forever. These ideas are part of Newton’s first law. </li></ul>
NEWTON’S SECOND LAW The acceleration a of an object in the direction of a resultant force F , is directly proportional to the magnitude of the force and inversely proportional to the mass m
Answer this to illustrate the first law of motion. <ul><li>In Enchanted kingdom, one of the rides was Jungle Log Jam. During the descent of the car from the top of the rail, why did you pitch forward when the car slowed down? </li></ul>
Newton’s Second Law Explained! The Law of Acceleration: Experience tells us that larger and larger resultant forces on the same object will result in greater and greater changes in the velocity of the object. F 2F a 2a
Furthermore: If we keep the resultant force constant and apply it to greater and greater masses, the change in velocity decreases. The change in velocity per init time is defined as its acceleration a . He demonstrated the direct relationship between the applied force and the resulting acceleration. He showed that the acceleration decreased proportionally with the inertia or mass of the object. a = — or F = ma F m
m 2m 3m F F F a ½ a CONSTANT FORCE INCREASING MASS RESULTS IN DECREASING VELOCITY ? 1. 2. 3. What would be the acceleration of no. 3?
We can deduce that: <ul><li>Acceleration, a is directly proportional to the resultant force, F and inversely proportional to the mass, m . </li></ul>a = — F m
NEWTON’S THIRD LAW FOR EVERY ACTION THERE MUST BE AN EQUAL AND OPPOSITE REACTION FORCE
Newton’s Third Law Explained <ul><li>There can be no force unless two bodies are involved . When a hammer strikes a nail, it exerts an “action” force on the nail. But the nail must also “react” by pushing back against the hammer. In all cases, there must be an acting force and a reacting force . Whenever two bodies interact, the force exerted by the second body on the first (the reaction force) is equal in magnitude and opposite in direction to the force exerted by the first body n the second (the action force). </li></ul>
Illustrating the 3 rd Law of Motion The wheels of the car push on the road. The road pushes the wheels of the car. ACTION FORCE: REACTION FORCE:
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