Newton’s Third Law of Motion: Action-Reaction 8SCIENCE
Review: what are Newton’s Laws of Motion? First law of motion: If forces acting on an object are balanced the object will remain at rest or in motion (constant velocity) Also called: Inertia Second law of motion: If forces are unbalanced, an object affected by a force will accelerate in the direction of the force Involves: Force and acceleration
Newton’s third law of motion Law: Forces always act in equal but opposite pairs Another way to say this: for every action there is an equal but opposite reaction One object cannot provide a force without this object causing a return force Forces act in opposite directions Ex: bumper cars, walking
Newton’s third law of motion: Sometimes it may be hard to identify the action-reactionpairbecause one object is much larger than the other It has so much inertia that it stays still or hardly accelerates Ex. Walking: when you walk forward you push your foot backwards on the ground. The Earth pushes your shoe forwardbut because the mass of the Earth is so large, it does move when you push against it Ex. Putting your hand out of the window in a moving car – force of the wind pushes your hand back in the opposite direction the car is moving Can you think of more examples?