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Session 2: Gravity

Start thinking: If gravity on Earth suddenly switched off for five seconds, what would happen first?

C

D

B

A

The oceans and atmosphere would start drifting away.

Nothing would happen.

Buildings would collapse.

Everyone would instantly fly into space.

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Because nothing is holding them down.

C

Gravity holds everything down so, without it, nothing stays in place.

Without gravity, those things would begin to drift away from Earth immediately because Earth is spinning and air molecules are in constant motion.

We would not fly into space straight away because we have no force pushing us upward, but the air and water around us would start to go.

The oceans and atmosphere would start drifting away.

REVEAL: C. Gravity holds the atmosphere, oceans and loose objects in place. If gravity suddenly disappeared on Earth, you would not magically shoot straight up into the sky. Gravity pulls you down, but its absence is just a lack of downward pull. Without an initial upward push or force, objects do not automatically move upward; they simply lose their weight and float or drift slightly where they are

Stretch the conversation:

If gravity disappeared, what would happen to the air around us?
If gravity is invisible, how do we know it is there?
Is gravity only important on Earth, or does it affect everything in space?
What would happen to the Moon if Earth's gravity switched off?

Bridge: Today we are going to find out what gravity actually is, where it comes from, and why it is the force that holds the entire universe together. It is not just about keeping your feet on the ground. Gravity is the reason planets are round, why the Moon does not fly off into space, and why we have 24-hour days instead of six-hour ones. Start the pathway now."

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Today’s Big Question:

Why is gravity the invisible architect of

the universe?

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Why is gravity the invisible architect of the universe?

PATHWAY 1

What is Gravity?

Mass generates gravity
Rank cosmic objects by pull
The Earth-Moon tug of war

10 mins

PATHWAY 2

What Does Gravity Do?

The equal squeeze
Weight versus mass
The golden distance rule

10 mins

Finished? Complete the What is Gravity Minigame

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Which is stronger?

Compare the two scenarios. Which scenario would have stronger gravity? There may be some where the answer is ‘it depends’ - be ready to explain your answer.

A
You are 100 km above Earth in a rocket.

B
You are 200 km above Earth in a rocket.

STRONGER

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Which is stronger?

A
You are on Venus (more mass).

B
You are on Mars (less mass).

STRONGER

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Which is stronger?

STRONGER

A
Mercury when it is at it’s furthest point from the Sun.

B
Mercury when it is at it’s closest point to the Sun.

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Which is stronger?

A
Standing on Earth.

B
Standing on a planet with Earth’s mass but twice the diameter.

STRONGER

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Which is stronger?

A
A spacecraft 10,000 km from the centre of the Moon.

B
A spacecraft 10,000 km from the centre of the Earth.

STRONGER

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Which is stronger?

A
The Earth’s pull on a 1 kilogram bag of sugar

B
The Earth’s pull on a 10 kilogram bowling ball

STRONGER

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Which is stronger?

A
You are standing on Mars (if that was possible).

B
You are standing on the Moon.

STRONGER

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Which is stronger?

A
The Sun’s pull on you, right now.

B
Earth’s pull on you, right now.

STRONGER

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Which is stronger?

A
Earth’s pull on an astronaut travelling to the Moon.

B
The Moon’s pull on the same astronaut.

IT DEPENDS

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Which is stronger?

A
You are standing on Earth.

B
A planet with twice Earth’s mass and twice its radius.

STRONGER

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Which is stronger?

A
The Sun’s pull on a probe heading for Proxima Centauri.

B
Proxima Centauri’s pull on the same probe.

IT DEPENDS

Note - Proxima Centauri has about 12% of the Sun’s mass.

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WE HAVE COVERED:

What gravity is

The two rules of gravity

Why planets and stars are spherical

How the Moon acts as a gravitational brake on Earth’s rotation

What would change on Earth without the Moon’s gravitational influence

Learner Journal

Part 1: Three Things I Learnt Today

Open your Learner Journal. Write down three things you learnt. These can be facts, ideas, or things that surprised you.

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If gravity became twice as strong on Earth tomorrow,

what would change and what would stay the same?

Write your response in your Learner Journal, then ﬁnish sections 3-5.

Learner Journal

Part 2: Reflective Question

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"Gravity is the weakest of the four forces by a long way; it is so weak that we would not notice it at all were it not for two special properties that it has: it can act over large distances, and it is always attractive.” Stephen Hawking, scientist (1988)

Every time you pick up an object, your arm muscles beat the gravitational pull of the entire Earth. But at the scale of the cosmos, gravity wins every time. That is what makes it the invisible architect of everything.

Lock-In Quote

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Extension Activities

Extension 1

Extension 2

Beating Gravity

Super Moon