Inertia!Inertia!

HistoryHistory

~300 B.C.E. Aristotle (Greek)~300 B.C.E. Aristotle (Greek) Divided motion into two Divided motion into two

categories:categories: Natural motion: straight up or Natural motion: straight up or

straight downstraight down Violent motion: result of forceViolent motion: result of force

Any movement “against nature” Any movement “against nature” was because of a forcewas because of a force

Everything rests on Earth; Earth Everything rests on Earth; Earth is too big to moveis too big to move

CopernicusCopernicus

~1500 C.E.~1500 C.E. Studied astronomyStudied astronomy Observed that astronomy Observed that astronomy

worked better if Sun was worked better if Sun was center of solar systemcenter of solar system

Theorized that the Earth did Theorized that the Earth did movemove

GalileoGalileo

~1600 C.E.~1600 C.E. Argued that objects only stop Argued that objects only stop

moving because of moving because of frictionfriction Friction: force that opposes Friction: force that opposes

movementmovement Occurs between two touching Occurs between two touching

objectsobjects :., objects in motion should :., objects in motion should

stay in motion without frictionstay in motion without friction

InertiaInertia

Galileo called this idea Galileo called this idea inertiainertia Inertia allows objects to resist Inertia allows objects to resist

changes in motionchanges in motion

NewtonNewton

~1700 C.E.~1700 C.E. Re-stated Galileo’s ideas in his 1Re-stated Galileo’s ideas in his 1stst law law

of motionof motion Objects continue at rest or in Objects continue at rest or in a straight a straight

line at a uniform speedline at a uniform speed, unless acted , unless acted on by a nonzero net forceon by a nonzero net force

Newton’s First Law of motion (aka law Newton’s First Law of motion (aka law of inertia)of inertia)

VocabularyVocabulary

FrictionFriction InertiaInertia Law of inertiaLaw of inertia MassMass WeightWeight newtonnewton

Objects at restObjects at rest

An object at rest will stay there An object at rest will stay there unless an outside force acts upon itunless an outside force acts upon it

That force upsets the equilibrium and That force upsets the equilibrium and will start the object movingwill start the object moving

Objects in motionObjects in motion

Once in motion, the net force Once in motion, the net force becomes zero againbecomes zero again

Only another force will make it slow Only another force will make it slow down or change directiondown or change direction

What does the amount of inertia What does the amount of inertia depend on?depend on?

MassMass

Mass is not…..Mass is not…..

Volume (a large size does not equal a Volume (a large size does not equal a large mass)large mass)

Weight (weight depends on gravity, Weight (weight depends on gravity, which is different in different places)which is different in different places)

Mass is InertiaMass is Inertia

MassMass is the amount of matter in an is the amount of matter in an objectobject

The more mass, the more inertia an The more mass, the more inertia an object hasobject has Mass is measured in kilograms (kg)Mass is measured in kilograms (kg)

WeightWeight is the force of gravity is the force of gravity Weight is measured in newtons (N)Weight is measured in newtons (N)

Relative MotionRelative Motion

Does a rock move sideways as it Does a rock move sideways as it falls?falls?

Why doesn’t it, if the Earth is Why doesn’t it, if the Earth is moving?moving?

Relative MotionRelative Motion

Objects move with the earthObjects move with the earth The rock is moving with the earth as The rock is moving with the earth as

it falls, so it does not seem to move it falls, so it does not seem to move sidewayssideways

Relative MotionRelative Motion

Relative MotionRelative Motion

High speed vehicles demonstrate this High speed vehicles demonstrate this concept.concept.

Dropping a rock in a plane has the Dropping a rock in a plane has the same effect.same effect.

The rock moves with the planeThe rock moves with the plane