Concept SummaryBatesville High School Physics

Aristotle’s ViewTwo types of motion:Natural motion - what an object

“naturally wants to do”Violent motion - what an object has to

be forced to do

Aristotle’s View In order for a “normal” object to move at

constant velocity, something must be pushing on it. When the pushing stops, the object (perhaps gradually) comes to a stop.

Galileo’s ViewRealized that the classical view of

motion did not recognize the role of friction

If left to themselves, moving objects don’t slow down.

Newton’s First LawWhatever an object is doing, that’s what

it wants to keep doing. If left to themselves, objects will keep

doing whatever they’re doing.

Newton’s First LawObjects at rest tend to stay at rest.Objects in motion tend to stay in motion.

Newton’s First Law

If there is no net force on an object, the object won’t accelerate.

Newton’s First Law

The converse is also true:If an object is not accelerating, then

there is no net force on it.

What is an “object”?

Anything made of matter is an “object”.

What is a “force”?

A force is an interaction between 2 objects involving a push or a pull.

Forces are vectors - they have a direction in space.

Common units of force are: pounds, Newtons, or dynes.

What is a “net force”?The net force on an object is the vector

sum of all of the forces that push or pull on the object.

“no net force on an object” means:

either there are no forces on the object, or:

the forces that push or pull on the object all cancel exactly.

“object won’t accelerate” means:

the object:won’t speed up.won’t slow down.won’t change direction.

Newton’s First Law can be stated:

If no forces push or pull on an object, or if the forces that do push or pull on it all cancel exactly, then the object will not speed up, slow down, or change direction.

InertiaNewton’s First Law says that objects do

not accelerate spontaneously.This property of matter, which causes

objects to resist acceleration, has been named “inertia”.

Newton’s First Law is often called the Law of Inertia.

Equilibrium

An object that is not accelerating is said to be “in equilibrium.”

If an object is at rest and not accelerating, it is said to be “in static equilibrium.”

Newton’s First Law Again

If an object is in equilibrium, the net force on it is zero, and

If the net force on an object is zero, the object is in equilibrium.

FrictionFriction is a force that arises due to the

relative motion of two surfaces. Two solid surfaces - sliding friction, rolling

friction A solid and a fluid - air resistance Two fluids

FrictionThe direction of the friction force always

opposes the relative motion of the surfaces.

FrictionThe amount of sliding friction depends

on: The condition (smoothness/roughness) of

the surfaces The normal force between the surfaces

The End

FrictionThe amount of sliding friction does not

depend on: Area of contact Relative speed