Chapter 2: Newton's First Law of Motion - Inertia

Aristotle

thought the natural state of objects on Earth is at rest. A force is needed to keep something moving

Galileo

showed with inclined planes that a force is not needed to keep an object moving.

friction

what slows things down

Ball rolling up a less steep second incline rolls

farther

on a flat, frictionless surface it would keep going ____ at constant speed

forever

newton’s first law

every object continues in its state of rest, or of uniform motion in a straight line, unless acted on by a net force

inertia

the property of an object to resist changes in their state of motion.

more mass

more inertia

mass

amount of matter (and inertia)

unit for mass

kg

weight

the force of gravity on an object

unit for weight

newton (n)

net force

the combination of all forces acting on an object

forces in the same direction

add

forces in opposite directions

subtract

net force is zero

an object at rest stays at rest, or an object in motion stays in motion

an object resting on a table

the support force equals its weight and points the opposite way

applied force

a push or pull on the object (direction of the push)

friction force

resists motion between surfaces (opposite the motion)

normal (support) force

surface pushes back on object (up, away from surface)

weight force

force of gravity on the object (down, toward the Earth)

bus stops suddenly

your body keeps moving forward. no force pushing you forward

tablecloth yanked out

dishes tend to stay at rest

ball tossed straight up

lands in your hand because it keeps the forward motion it shares with earth, even though earth is moving