FORCES

Is gravity real - or does the Earth just suck?

2

What do forces do?

Make things ----

move

move faster

move slower

change direction

also

change shape

3

Big and Little forces

We can measure forces

Using a forcemeter

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Sir Isaac

Newton

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Which fruit ?

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Newton?

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Now a game!

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Lifting a ping pong ball

.

straw

Suck !

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ping pong ball falling

The arrow represents the force of gravity

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The ball does not fall when your

sucking force = force of gravity

straw

Suck

gravity

How have I shown this ?

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Which diagram shows the sucking

force equal to the force of gravity?

straw

Suck

gravity

straw

Suck

gravity

straw

Suck

gravity

Newton

metric unit of force

What is gravity?

Sir Isaac Newton

1642 – 1727

The Principia

Gravity

force of attraction between all objects in

the universe

Gravity

the larger an object’s mass, the greater

the gravitational force

Gravity

the greater the distance between two

objects, the smaller the gravitational force

the force of gravity decreases by the amount

equal to one divided by the distance (d)

squared

1/d2

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The ball does not fall when your

upward force = force of gravity

straw

Suck

gravity

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Gravity down under

People do not fall off the Earth

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two objects dropped at the same time

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On the Moon – Apollo 15

http://nssdc.gsfc.nasa.gov/planetary/image/featherdrop_sound.mov

A heavy geological hammer and a falcon feather were dropped from the same height.

They hit the lunar surface at the same time.

astronaut David Scott

NASA pictures

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Hippo jump

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Hippo jump

Force of gravity

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Saved?

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Hippo is still falling quickly

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Hippo is still falling quickly but not getting faster

How do we know?

Force of gravity

air resistance

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How can we slow Hippo down?

What can you change?

Air Pressure

air pressure is caused by the motion of

particles in the air

you do not feel the weight of the air

because the pressure inside your body is

equal to the air pressure around you

Air Pressure

air pressure changes with altitude

the higher you are, the lower the air pressure

Air Pressure

Barometer

instrument used to measure air pressure

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Launching a satellite

The cannon ball must move very quickly to orbit the earth.

The Moon

orbits the Earth

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The Moon

The Earth

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The Moon

The Earth

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On the Moon

NASA pictures

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Very heavy boots- Why?

Answers? No gravity on the Moon Weightless on the Moon To stop them floating away They weigh very much less than on Earth To stop huge bounces The Moon’s gravity is very much less than the

Earth’s gravity

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Weightless?

or are they?

(NASA pictures)

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apparently weightless (pictures or animation only –not a demonstration)

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GRAVITY

Things fall

Things have weight

Things stay in place

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No Gravity Would an apple fall? Would things stay on earth? What would happen?

What? Why? How?

keep asking questions -like Newton !