ObjectivesObjectives

To understand ……To understand …… what what gravitygravity, , massmass and and weightweight are. are. how gravity changes. how gravity changes. how the weight changes of an object.how the weight changes of an object. what affects gravity.what affects gravity. orbits of planets and satellites.orbits of planets and satellites.

What do gravity, mass and weight all What do gravity, mass and weight all have in common?have in common?

Forces can:Forces can:1.1. Change speed of an objectChange speed of an object2.2. Change direction of objectChange direction of object3.3. Change the size or shape of an objectChange the size or shape of an object

FORCES

Force of attraction between 2 masses.Force of attraction between 2 masses.

Not just on Earth but everywhereNot just on Earth but everywhere

It can only pull not push.It can only pull not push.

Acts towards centre of Earth.Acts towards centre of Earth.

Amount of Amount of MATTERMATTER in an object. in an object.

Measured in Measured in kilogramskilograms (kg). (kg).

4 kg0.1 kg

Not to scale

•Stays the same Stays the same anywhere you go.anywhere you go.

A downward-pulling force on an object due to A downward-pulling force on an object due to gravity.gravity.

Measured in Measured in NewtonsNewtons (N) (N) Changes depending on where you are.Changes depending on where you are.

Where would the flag be lighter?Where would the flag be lighter?On Earth On Moon

In order to calculate mass or weight of In order to calculate mass or weight of an object you need the gravitational an object you need the gravitational field strength.field strength.

On Earth it is approx On Earth it is approx 10 N/kg10 N/kg

WEIGHT= MASS x G.F.S(N) (kg) (N/kg)

You need to remember this!!

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

2.2. Calculate the mass of a man who has Calculate the mass of a man who has a weight of 750N.a weight of 750N.

3.3. What is the weight of a pushchair What is the weight of a pushchair which has a mass of 7kg?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)

What is gravity again?What is gravity again?

The force of The force of attraction for a larger attraction for a larger object is greater than object is greater than smaller one.smaller one.

•The force of attraction The force of attraction between 2 masses between 2 masses decreases as you go decreases as you go further apart.further apart.

The g.f.s changes The g.f.s changes on different on different planets.planets.

Newton said the Newton said the moon is caught moon is caught between 2 forces:between 2 forces:

1.1. GravityGravity

2.2. Centrifugal forceCentrifugal force

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

1.1. The speed the The speed the planet moves .planet moves .

2.2. The time to The time to complete an complete an orbit .orbit .

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

They pass They pass continuously over continuously over north and south north and south poles.poles.

Geostationary Geostationary satellites – e.g. satellites – e.g. comunication and comunication and navigation.navigation.

Travel at same Travel at same speed as Earth.speed as Earth.