It’s Universal – it’s everywhere!

Gravity

What two factors affect the force of Gravity?

Force Boson

(composite particle)

Function Range

Gravity Graviton Gravity curves space. And it

always attracts, never repels.

Gravity is the only force to

which all particles are subjected.

Indefinite

(property of

matter)

Strong Nuclear

Force

Gluon (8 kinds) The strong force binds quarks

into nucleons and nucleons into

nuclei.

Limited to the

atomic nucleus

(Nuclear Force)

Electromagnetism Photon Electromagnetism binds

electrons to the nucleus. By

doing so electromagnetism

allows all physical and chemical

processes to happen.

Indefinite

(property of

matter)

Weak Nuclear

Force

Weak bosons

(3 kinds)

The weak force causes unstable

particles and nuclei to decay.

Limited to the

atomic nucleus

(Nuclear Force)

The Standard Theory

Newton’s Law of Universal Gravitation

G is a very small number (0.0000000000667)

Gravity is a weak force, this means that the force of

gravity is not noticeable unless there is a very large

mass involved (such as a planet or star).

That’s why we are not

revolving around one

another!

But the Earth and Moon

are large enough!

Gravity is universal –

it’s everywhere!

Gravity depends on mass

(amount of atoms)

More mass means more

gravitational force

Less mass means less

gravitational force

Newton’s Law of Universal Gravitation

Gravity pulls objects in a straight line towards each other.

Earth and Moon

Gravity depends on the distance

between objects

Less distance means

more gravitational force

More distance means

less gravitational force

Think of gravity like a

magnet. When magnets

are closer, the attraction is

stronger. When magnets

are further apart, the

attraction is less.

It’s Universal – it’s everywhere!

Gravity

What two factors affect the force of Gravity?

MASS DISTANCE

Gravity

Gravitational Force

Affected by mass and distance

The amount of Newtons that gravity pulls on an object

Gravitational Acceleration

How fast an object falls due to gravity

Called little g

On earth little g = 9.8m/s/s

So an object speeds up by about 10m/s every second when falling

On the moon little g = 1.6m/s/s

So an object speeds up by about 2m/s every second when falling

F = ma

Force of gravity will

accelerate a mass.

Gravitational Acceleration

So all objects “want” to fall at 9.8m/s/s on the surface of the earth.

Gravity mini-experiment:

1. Crumble up (compress) a piece of paper.

2. Drop the paper from the height of your desk to the floor.

3. Leave a piece of paper flat.

4. Drop the paper from the height of your desk to the floor.

5. Observe how each object falls.

Discussion:

Both object “want” to fall at 9.8m/s/s. Did each object fall at the

same rate downward? What did each object have to push through?

What would happen if the paper had nothing to push through?Hammer vs Feather – Physics on the Moon

APOLLO 15

THE HAMMER AND THE FEATHER

All objects fall at the same rate in a

gravitational field. Normally air resistance

would slow down the feather. On the moon

there is no air so it is easy to see that

gravitational fields accelerate all objects at

the same rate.

ADJUSTING TO LIFE BACK ON EARTH

Astronauts in Space

Washing your hair in

space!

Washing your bald

head in space?

Sometimes astronauts

have a little trouble

adjusting to life back

on Earth

Adjusting to Life back

on Earth Text: Zoltan Otvos

Graphics: Andras Danscak

Source: NASA/Nepszabadsag Graphics

Gravitational Acceleration

All objects on the surface of the earth accelerate downward at

9.8 m/s2 regardless of mass. Why? (Think about inertia…)

100 kg

10 kg

Gravitational acceleration

g = 9.8 m/s2

Gravitational acceleration

g = 9.8 m/s2

More mass means more gravity, but it also means more

inertia. The extra gravity gets cancelled out by the extra

inertia, so all objects fall at the same speed regardless of mass.

Remember F=ma As the force and mass change the acceleration stays the same.

Once the altitude becomes comparable to the radius of the

Earth (a distance thousands of miles away from earth), then

the gravitational acceleration becomes much smaller.

Gravitational Acceleration

Once you are about 20,000 miles

above the surface, there is little gravity

– this is known as microgravity.

WeightGravity’s Effect on Mass

Weight is a Force measured in Newtons

Weight = Mass x Acceleration of Gravity

9.8 (Newtons) =1 (kg) 9.8(Meters/Sec2)

W(Newtons) = m (kg) g(Meters/Sec2)

As you travel further from the surface of earth, increasing distance,

then the gravitational force and gravitational acceleration decrease. If

you travel far enough then you have apparent weightlessness.

Word Magnet: What is Gravity?

Gravity

Attractive force

Property of

Matter

Considered to

be a weak force

One of the four

forces of nature

Gravitational Force

depends on the

total mass of the

two objects

Gravitational Force

depends on the

distance between the

two objects

GRAVITY TENNIS

Procedure:

1. Hold one tennis ball at the height of the counter.

2. Roll the second tennis ball from the back of the counter to the front edge.

3. Once the roll ing ball reaches the edge of the counter, let go of the first tennis ball .

4. Observe the motion of each ball and repeat for several trials.

Discussion Questions:

Did the tennis balls hit the

ground at the same time?

Explain.

How fast do objects “want”

to fall vertically on the

surface of Earth?

Does horizontal motion

influence or change the

vertical motion?

INVESTIGATING GRAVITY

INVESTIGATING GRAVITY

INVESTIGATING GRAVITY

Think about Newton’s First Law?

Does the cup have mass?

Does the water have mass?

Are the cup and water moving at the same rate?

How fast does little g “want” to accelerate all objects?

Chapter 3.1 – Gravity

Topic: What affects the force of gravity?

Vocabulary (Define in your notebook):Gravity

Weight

Orbit

Procedure: Complete using Window Notes

Define the vocabulary words in your notebook. Paragraph

read section 3.1 (pages 76-83) with your lab group.

Answer questions 1-6 on page 83 in your science notebook

Extension Activity - Gravity and Orbits Interactive