I NERTIA AND N EWTON ’ S F IRST L AW OF M OTION

DEMO TIME History of Physics:

ARISTOTLE Lived in Greece Born 384 BC Died: 322 BC Believed that unequal masses Reach the ground at different time All movement required forces Proper state was of rest – all objects will eventually come to rest. Stood for 2000 years

GALILEO Lived in Italy Born: 1564 Died 1642 Believed unequal masses fell at the same time

G ALILEO ’ S THOUGHT EXPERIMENT Galileo observed objects return to original position regardless of incline Therefore, object’s “natural” state is not of rest They resist changes in motion - inertia

Observed that inclines change velocity The smoothness of surface directly effected motion With no friction (surface or air), how does speed change on a level surface?

I NERTIA A property of matter that causes an object to resist changes in its state of motion; it is directly proportional to the mass of the object. Inertia = laziness = an object’s resistance to change

N EWTON ’ S FIRST LAW / LAW OF INERTIA : Objects at rest or moving with a constant velocity maintain their state of rest or constant velocity unless acted upon by an external, unbalanced force.

I NERTIA AND CAR CRASHES This law of inertia helps us to understand the principles behind using seatbelts and air bags. Once an object is moving, it tends to keep moving at a constant velocity because of its inertia. Air bags and seatbelts help to slow us down safely.

E XAMPLES OF I NERTIA pulling tablecloth out from under dishes card and glass Coin into cup