Inertia!
History ~300 B.C.E. Aristotle (Greek) Divided motion into two categories: Natural motion: straight up or straight down Violent motion: result of force Any movement “against nature” was because of a force Everything rests on Earth; Earth is too big to move
Copernicus ~1500 C.E. Studied astronomy Observed that astronomy worked better if Sun was center of solar system Theorized that the Earth did move
Galileo ~1600 C.E. Argued that objects only stop moving because of friction Friction: force that opposes movement Occurs between two touching objects :., objects in motion should stay in motion without friction
Inertia Galileo called this idea inertia Inertia allows objects to resist changes in motion
Newton ~1700 C.E. Re-stated Galileo’s ideas in his 1st law of motion Objects continue at rest or in a straight line at a uniform speed, unless acted on by a nonzero net force Newton’s First Law of motion (aka law of inertia)
Vocabulary Friction Inertia Law of inertia Mass Weight newton
Objects at rest An object at rest will stay there unless an outside force acts upon it That force upsets the equilibrium and will start the object moving
Objects in motion Once in motion, the net force becomes zero again Only another force will make it slow down or change direction
What does the amount of inertia depend on? Mass
Mass is not….. Volume (a large size does not equal a large mass) Weight (weight depends on gravity, which is different in different places)
Mass is Inertia Mass is the amount of matter in an object The more mass, the more inertia an object has Mass is measured in kilograms (kg) Weight is the force of gravity Weight is measured in newtons (N)
Relative Motion Does a rock move sideways as it falls? Why doesn’t it, if the Earth is moving?
Relative Motion Objects move with the earth The rock is moving with the earth as it falls, so it does not seem to move sideways
Relative Motion
Relative Motion High speed vehicles demonstrate this concept. Dropping a rock in a plane has the same effect. The rock moves with the plane