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**Gravity and Space Objectives To understand ……**

what gravity, mass and weight are. how gravity changes. how the weight changes of an object. what affects gravity. orbits of planets and satellites.

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**Gravity, Mass and Weight**

What do gravity, mass and weight all have in common? Forces can: Change speed of an object Change direction of object Change the size or shape of an object FORCES

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**Gravity Force of attraction between 2 masses.**

Not just on Earth but everywhere It can only pull not push. Acts towards centre of Earth.

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**Mass Amount of MATTER in an object. Measured in kilograms (kg).**

Not to scale 4 kg 0.1 kg Measured in kilograms (kg). Stays the same anywhere you go.

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Weight A downward-pulling force on an object due to gravity. Measured in Newtons (N) Changes depending on where you are. Where would the flag be lighter? On Earth On Moon

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**Calculating Weight and Mass**

In order to calculate mass or weight of an object you need the gravitational field strength. On Earth it is approx 10 N/kg WEIGHT= MASS x G.F.S (N) (kg) (N/kg) You need to remember this!!

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**Calculate the mass of a book which has a weight of 10N.**

Calculate the mass of a man who has a weight of 750N. What is the weight of a pushchair which has a mass of 7kg? REMEMBER the gravitational force strength is 10N/kg on Earth. WEIGHT= MASS x G.F.S (N) (kg) (N/kg)

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**How does Gravity change?**

What is gravity again? The force of attraction between 2 masses decreases as you go further apart. The force of attraction for a larger object is greater than smaller one. The g.f.s changes on different planets.

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**Sir Isaac Newton Newton said the moon is caught between 2 forces:**

Gravity Centrifugal force

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**Orbits As planets get further away from Sun:**

The speed the planet moves . The time to complete an orbit .

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**Satellites Polar satellites – e.g. weather. Travel in low polar orbit.**

They pass continuously over north and south poles. Geostationary satellites – e.g. comunication and navigation. Travel at same speed as Earth.

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Comets

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