Newton’s Three Laws of Motion Sir Isaac Newton first presented his three laws of motion in the Principia Mathematica Philosophiae Naturalis in To understand Newton’s laws of motion, you must remember that on Earth we always have GRAVITY pulling down on us and AIR around us. Newton’s laws are used in the design of aircraft and spacecraft.
First Law of Motion Objects in motion tend to stay in motion AND Objects at rest tend to stay at rest UNLESS Something pushes or pulls on the object.
First Law of Motion Example Think of a block sitting still, or “at rest”. If the block is to move, it must receive a push. Otherwise it will stay at rest. Push
According to Newton’s First Law, When Will the Block Stop? Push Push
First Law of Motion Example Think of a baseball thrown in space. Without GRAVITY to pull it down, the ball would just keep moving until something got in its way and stopped it.
Aerospace Examples of the First Law of Motion The movement of an airplane changes when the pilot changes the throttle setting (or force) of the engine. More force moves the airplane at a greater speed.
Aerospace Examples of the First Law of Motion The movement of a model rocket being launched into the atmosphere The rocket was at rest (not moving) until the force of the engine pushed it upward.
Second Law of Motion The acceleration of an object depends on: –The size of the force on the object –The direction of the force on the object –The mass of the object The relationship: F = m * a Force = mass * acceleration Or a=F/m acceleration = Force/mass
Examples of Second Law of Motion The direction of acceleration is the same as the direction of the external force. Remember the box? If you want to move the box to the right, you push toward the right. If you want to move the box to the left, you push toward the left. Push
Examples of Second Law of Motion The magnitude (size) of the acceleration is equal to the external force divided by the mass of the object. The bigger the object (the more mass), the more force is needed to accelerate the object. Back to the box (but let’s add a car). If you push the car and the eraser with the same force, The eraser will accelerate much faster than the car. 50 lb 50 lbs
Third Law of Motion For every action, there is an equal and opposite reaction. You, on roller blades, push against a wall. Object A: You Object B: Wall Action: You apply a force on the wall. Reaction: The wall applies the same force back on you.
Examples of the Third Law of Motion You, on roller blades, push against a wall. Your backward movement is the result of the wall pushing back against you. Object A: You Object B: Wall
Examples of the Third Law of Motion Flaming hot gases are pushed out the bottom of a rocket. Object B: Rocket Object A: Flaming hot gas Action: Gas is pushed downward out of the rocket Reaction: The rocket moves upward
Third Law of Motion Examples The upward movement of the rocket is the result of the gases pushing downward from the rocket.
Third Law of Motion Key Points The third law can be used to explain how a wing produces lift and a jet engine produces thrust. On a wing, the air is pushed downward because of the wing’s unique shape (an airfoil). In reaction, the air pushes the wing upward. A jet engine produces hot exhaust gases which flow out the back of the engine. In reaction, a thrusting force is produced in the opposite direction.
Image Resources Microsoft, Inc. (2009). Clip art. Retrieved June 16, 2009, from National Aeronautics and Space Administration (NASA). (n.d.). Newton’s third law of motion. Retrieved June 19, 2009, from