1 st Law of Motion Courtesy of Sir Isaac Newton

Isaac Newton He lived from 1642 to He was a mathematician and physicist He lived from 1642 to He was a mathematician and physicist Legend: He saw an apple fall from a tree and came up with a theory of gravity. Legend: He saw an apple fall from a tree and came up with a theory of gravity.

Motion An object is in motion when that object changes position over time relative to a reference point An object is in motion when that object changes position over time relative to a reference point Reference point: an object that appears to stay in place (examples: Earth’s surface, trees, buildings, non-moving objects) Reference point: an object that appears to stay in place (examples: Earth’s surface, trees, buildings, non-moving objects)

Force A push or a pull A push or a pull The unit for force is called the Newton (N). The unit for force is called the Newton (N).

Forces continued … Unbalanced forces produce a change in motion. Unbalanced forces produce a change in motion. Balanced forces will NOT cause a change in motion. Balanced forces will NOT cause a change in motion. Net force is the combination of all forces acting on an object. Net force is the combination of all forces acting on an object.

A force that slows motion Can cause a moving object to slow down and stop. Occurs because the surface of any object is rough. Occurs because the surface of any object is rough.

Inertia The tendency of an object to resist change in motion. The tendency of an object to resist change in motion. Mass (the amount of matter in an object) is a measure of inertia. Mass (the amount of matter in an object) is a measure of inertia. The greater the mass, the greater the inertia. The greater the mass, the greater the inertia.

1 st Law of Motion (Law of Inertia) An object at rest will stay at rest, and an object in motion will stay in motion, unless acted upon by an unbalanced force.

Once an object is airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop! Once an object is airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!

Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever. Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force?

It’s a force we sometimes cannot see… Friction!

If you were to slide a book across a table it would eventually slide to a resting position. The book comes to a rest because of the presence of a force - that force being the force of friction - which brings the book to a resting position.

In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.)

Newton’s 1 st Law and You Do not let this be you! Wear your seat belt! Because of inertia, objects (including you) resist changes in their motion. When the car going 80 mph is stopped by the brick wall, your body keeps moving at 80 mph.