First we need to define the word FORCE: any influence that causes an object to change its movement, direction, or shape. Force is the cause of motion In other words, a force is needed to cause objects to move Two types of forces –Pushes –Pulls
Forces may be balanced or unbalanced Balanced forces – all forces acting on an object are equal –There is NO MOTION Unbalanced forces – one or more forces acting on an object are stronger than others –There is MOTION
Newton Sir Isaac Newton (1642-1727) Mathematician and physicist Discovered many things: –Laws of motion –Optics –Gravity –Calculus
Objects at Rest Objects at rest tend to stay at rest unless acted upon by a force. [push or pull] Newton described this tendency as inertia. Inertia can be described as the tendency of an object to keep doing whatever’s it’s doing.
Mass & Inertia Mass is the amount of matter in an object. The more MASS an object has, the more INERTIA the object has. Bigger objects are harder to start & stop Which vehicle has more inertia?
What about objects that are already in motion? Newton stated that objects in motion tend to stay in motion until acted upon by a force
Newton’s 1 st Law (also known as the law of inertia) A moving object moves in a straight line with constant speed unless a force acts on it. The tendency of an object at rest to remain at rest and an object in motion to remain in motion unless acted upon by an unbalanced force. Objects do not change their motion unless a force acts on them
The truck is in motion. What is the force that causes it to stop? The push of the stopped car. The car is at rest. What is the force that causes it to move? The push of the truck.
Concept Check How does the law of inertia account for removing dirt from your shoes by stamping on the porch before entering a house or removing dust from a coat by shaking it?
Earth’s Rotation The earth rotates at a speed of 1,040 mph. (Do you feel it?) If the Earth came to a sudden stop, and you jumped up into the air at that exact moment, would you land safely back on the ground?
Earth’s Rotation & Inertia Could you travel from San Francisco to New York by staying stationary in the air for 3 hours?