Newton’s First Law ( ) “The Law of Inertia” A body remains at rest or moves in a straight line at a constant speed unless acted upon by a net force. –Objects do not accelerate unless a net force is applied

Objects at rest remain at rest and objects in motion remain in motion, unless acted upon by an outside force. Newton’s 1 st Law of Motion

Newton’s 2nd law of Motion …mathematically Net Force = (mass)(accel) F net = ma

NEWTON'S 2 nd LAW OF MOTION F a m Fa mm F a m m m Fa Fa Fa M MM

When the acceleration is g we have Free Fall m F 2m 2F

Terminal Velocity Acceleration = g Acceleration < g Acceleration << g Acceleration = 0 Velocity = 0 but motion is about to begin v increasing downward v still increasing downward just not as rapidly as before Terminal velocity mg F F F Net Force

Falling with Air Resistance & Terminal Velocity When falling the force of air resistance becomes large enough to balance the force of gravity. At this instant in time, there is no net force — the object stops accelerating (see D below); terminal velocity has been reached.

Newton’s Third Law Action-Reaction When one object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction on the first object. Example of Newton’s 3 rd Law: hM7pDeI8/s1600-h/newton hM7pDeI8/s1600-h/newton

Newton’s Third Law of Motion For every action, there is always a reaction of equal (magnitude) and opposite (direction) reaction. “action” or “reaction” refers to force. Action/Reaction forces do NOT act on the SAME object!

Action: tire pushes on road Reaction: road pushes on tire

Action: rocket pushes on gases Reaction: gases push on rocket

Action- Reaction Forces Do Action-Reaction forces cancel each other? No, they are acting on different objects. Forces can only be added together when they are acting on the same object.

Newton’s 3 rd Law of Motion Action Force: A guy is pushing a ball leftwards Reaction Force: the ball is pushing the guy rightwards

Tug-a-war If Fido and Rover play tug-a war, how do the “pulls” of the dogs compare? If each dog pulls with 50 N of force, what is the tension force in the middle of the rope (between the dogs)?

While driving, Mrs. Ingle observed a bug striking the windshield of her car. The bug hits the windshield and the windshield hits the bug. Which of the two forces is greater: the force on the bug or the force on the windshield? EXPLAIN!

Putting Newton's Laws of Motion Together An unbalanced force must be exerted for a rocket to lift off from a launch pad or for a craft in space to change speed or direction (First Law). The amount of thrust (force) produced by a rocket engine will be determined by the rate at which the mass of the rocket fuel burns and the speed of the gas escaping the rocket (Second Law). The reaction, or motion, of the rocket is equal to and in the opposite direction of the action, or thrust, from the engine (Third Law). pacetoday.org /images/Rock ets/ArianeRo ckets/Ariane5 LaunchAriane space.jpg