Unit B

Chapter 3

Lesson 3

All objects resist

changes in motion.

Inertia and Motion• In the 1500’s scientist Galileo studied falling bodies. His

ideas were carried on by Isacc Newton. • Newton suggested that there were three laws of motion

that describe how objects move.• Newton's first law of motion states that an object stays at

rest unless some unbalanced force acts on it. If an object is in motion, it continues moving in a straight line unless some unbalanced force acts on it.

• Inertia is the resistance of an object to change in its state of motion. The more mass an object has the greater inertia.– Examples:

• Baseball player running • Stop short in a car

Inertia and Motion

• Inertia works here on Earth and in outer space.– Example: If an astronaut lets go of an object in space, it

keeps going in one direction until it hits something like the wall of a spaceship and changes direction.

• There is also inertia when traveling in a car. – When a driver suddenly stops, the passengers surge

forward, and if there wasn’t a seatbelt they would go flying out.

Friction

• Newton’s first law states that an object will continue moving UNLESS some outside force acts on it.

• Friction is the force between surfaces that resists movement of one surface past the other surface.– Examples:

• Roller blading• Ice skating

• Any kind of friction between two objects turns into thermal energy.– Examples:

• Stopping car• Rubbing hands together

• Colliding particles transfer energy between them.

Friction

• Air resistance- The friction from air molecules hitting an object as the object moves through the air .– Example:

• Parachutist jumping out of a plane• Feather falling

• Almost everything hits the ground at the same time besides objects that are affected by air resistance.

• Friction can be helpful. If friction disappeared you wouldn’t be able to slow down.

Circular Motion

• If things are supposed to be moving in a straight line, why do some go in circles? This is circular motion.

• Some examples of circular motion are:– throwing a ball– some amusement park rides (merry go round)

• The force that keeps an object in a circular motion doesn't have to be a pull, it can be a push.

Circular Motion in Action

• Astronauts use circular motion on every mission. They use it when they orbit the Earth.– They stay close enough to Earth that gravity

still pulls on the rocket. They need to balance inertia to stay in a circular orbit.