GravityIt’s Universal – it’s everywhere!

What two factors affect the force of Gravity?

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

Less mass means less gravitational force

More

mass

means

more

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 meansmore

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.

GravityIt’s Universal – it’s everywhere!

What two factors affect the force of Gravity?

MASS

DISTANCE

Gravitational AccelerationSo 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?

Answer in your notebook

APOLLO 15THE 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.

http://www.teachertube.com/video/hammer-and-feather-drop-on-moon-41342

Before you watch the video.

ADJUSTING TO LIFE BACK ON EARTH

Astronauts in Space

http://www.space.com/21946-how-to-wash-hair-space-video.html

Sometimes astronautshave a little trouble adjusting to life back on Earth

http://www.space.com/23672-adjusting-to-life-back-on-earth-karen-nyberg-talks-to-space-com-video.html

Washing hair in space:

Adjusting back to life on Earth:

Gravitational AccelerationAll objects on the surface of the earth

accelerate downward at9.8 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.

Write this in your notes!

WeightGravity’s Effect on Mass

Weight = Mass x Acceleration of Gravity

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

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

Weight is a Force measured in Newtons

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.

Read this slide!

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

Write this in your notebook!

INVESTIGATING GRAVITY

INVESTIGATING GRAVITY

Answer in your notebook

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?

Read through these before you look at the next slide. You do NOT have to answer these in your notebooks.

Chapter 3.1 – Gravity When you complete the

notes start working on your homework.