Gravity & Inertia

force of attraction

force of attraction

- Gravity is the force of attraction

between any two objects.

- It acts over a distance;

objects do not have to touch.

- It increases with the mass of objects.

- It increases as the objects get closer.

The Law states that...

The Law states that...

- any two bodies in the universe

attract each other with a force

- that is directly proportional to

the product of their masses and

- inversely proportional to the square

of the distance between them

things falling downward

things falling downward

- Earth’s gravity causes

things to fall downward.

- Without it, things would

be floating in the sky.

atmosphere around Earth

atmosphere around Earth

- Earth’s gravity keeps the

atmosphere from flying off

into space.

- This atmosphere absorbs

harmful ultraviolet radiation

and protects life on Earth.

resistance

to change

resistance

to change

- Inertia is the tendency of an

object to resist changes to its

state of rest or state of motion.

- The more mass an object has,

the greater its inertia.

The Law states that...

The Law states that...

- every object will remain at

rest or in uniform motion in a

straight line

- unless forced to change by the

action of an outside force.

motion in

a vehicle

motion in

a vehicle

- When you are riding in a

vehicle and it stops suddenly,

you keep moving forward.

- If you didn’t have a seat belt on,

you would be thrust forward

by inertia.

tablecloth trick

tablecloth trick

- You can quickly pull a tablecloth

from under some plates without

breaking them.

- The plates are not disturbed and

remain at rest because of inertia.

The Theory states that...

The Theory states that...

- The solar system was formed

from a spinning gas cloud.

- This sets planets and moons

into motion from the start.

Inertia keeps

Earth moving ahead...

Inertia keeps

Earth moving ahead...

- Sun’s gravity keeps pulling

Earth toward itself.

- Earth's forward motion is

balanced by Sun's pull on Earth.

- So Earth orbits around Sun.

Similarly...

Similarly...

Other planets orbit

around Sun because of

gravity and inertia.

If there was

only gravity...

If there was

only gravity...

the moon would be

pulled into the Earth.

If there was only inertia...

If there was only inertia...

the moon would move off through space in a straight line.

Inertia keeps Moon moving ahead...

Inertia keeps Moon moving ahead...

- Earth’s gravity keeps pulling

Moon toward itself.

- Moon's forward motion is

balanced by Earth's pull on Moon.

- So Moon orbits around Earth.

Tides are the rise

and fall of sea levels...

Tides are the rise

and fall of sea levels...

They are caused by the pull of gravity from

the Moon (mainly)

and the Sun.

due to gravity on

the side nearest Moon

due to gravity on

the side nearest Moon

- the force of gravity between Earth

and Moon is greater than the inertia

- so the ocean water is pulled

towards Moon

- forms a tidal bulge

due to inertia on the

side farthest from Moon

due to inertia on the

side farthest from Moon

- the force of gravity between

Earth and Moon is less than the inertia

- so the ocean water tries to keep

going in a straight line, moving

away from the Earth

- forms a tidal bulge

Have you ever wondered?

Have you ever wondered?

Why don't riders fall out when a roller coaster goes upside down?

when going

around a loop...

when going

around a loop...

Inertia is the force that presses your body to the outside of the loop as the roller coaster turns around.

At the top

of the loop...

At the top

of the loop...

- The force of acceleration due to

the motion of the roller coaster is

stronger than the force of gravity.

- This force of acceleration pushes

riders into their seats and

stops them from falling out,

even without a safety harness!