Newton’s First Law (1642-1727) “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.

Newton’s 1st Law of Motion Objects at rest remain at rest and objects in motion remain in motion, unless acted upon by an unbalanced force. http://talesfromechocanyon.blogspot.com/2007_03_02_archive.html

Newtons’ Second Law The accel. of an object is directly proportional to the net force acting on the object, and inversely proportional to the mass of the object.

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

NEWTON'S 2nd LAW OF MOTION

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

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

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 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 3rd Law: http://bp3.blogger.com/_vQA3QRUnk3M/RrgyfrRniPI/AAAAAAAAAMs/DYlhM7pDeI8/s1600-h/newton

Newton’s Third Law of Motion There is an interaction between objects. Each opposing force has equal magnitude and opposite direction. This is an interaction, the forces do NOT act on the SAME object! Ex: Man pushes UP on barbell, barbell pushes DOWN on man.

Tire pushes road backwards Road pushes tire forwards

Gases push rocket forward Rocket pushes gases backwards

Newton’s 3rd Consider forces between two or more objects that are touching. The forces act on different objects. Forces can only be added together (to solve for net force) when the forces act on the same object. http://quest.nasa.gov/space/teachers/rockes/principles.html

Newton’s 3rd Law of Motion The guy pushes a rock up the hill The rock pushes the guy down the hill

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)?

Simplified: Bug hits windshield and windshield hits bug. The driver of a car observed bugs splattering on the windshield of his car. Simplified: Bug hits windshield and windshield hits bug. How does the force of the bug ON the car windshield compare to the force of the car windshield ON the bug? Are the forces unequal or equal in magnitude? Are the forces in the same or opposite direction? 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). http://www.spacetoday.org/images/Rockets/ArianeRockets/Ariane5LaunchArianespace.jpg http://quest.nasa.gov/space/teachers/rockets/principles.html