UNIT 9J

Gravity and Space

• Explain the difference between mass and weight

• Describe gravity

LEARNING OUTCOME

Weight and Mass

Weight and mass are not the same.Mass is the amount of matter in an object.

This will have the same value anywhere in the Universe including space.

Weight is a force and it is caused by the pull of gravity.

In fact, weight is the pull of gravity acting on a mass.

Weight is a force so is measured in Newtons.

Like other forces it has both magnitude (Size) and direction.

Mass is not a force, it is measured in kilograms.

An astronaut could jump 20 feet into the air on the moon because gravity is less.

Would his mass change? And his weight?

Weight and Mass

Planet Mass (kg) g-value (N/kg) Weight (N)

Mercury 3

Venus 9

Earth 10

Mars 4

Jupiter 26

Saturn 11

Uranus 11

Neptune 12

Pluto 0.5

Weight (N) = Gravitational Field Strength (N/kg) x Mass (kg)W = g x m

Use the mass balance to find the mass of an object.Now calculate the weight of this object on other planets in the Solar System.

Weight and Mass

So, a scientist should NEVER say “He weighs 50kgs” but, should say

“He has a mass of 50kgs”,

or the scientist could say:

“the gravitational force acting on his mass is about 500 Newtons”.

This is the same as saying:

“his weight is about 500 Newtons”.

Gravity

Gravity is an attracting force

Everything has gravity

Think about it:

When you jump the gravitation force of the Earth pulls you down. Your gravitation force pulls the Earth up!

Force of gravity

Earth - large mass

Space shuttle- smaller mass

The force of gravity depends on the mass of the planet and how close you are to it.

GRAVITATIONAL FORCE

Mass = 100g Mass = 100g

The force of gravity between 2 apples is very small as they don’t have much mass.

Mass = 100g

Mass = billions of tonnes

The force of gravity between anApple and earth is large becauseEarth has a very high mass.

• Explain why objects weight less on the moon than on the earth.

• Describe the effects of the gravitational pull of other planets on the earth.

• Explain how rockets can leave the gravitational pull of the earths surface.

LEARNING OUTCOME

The Solar System

The planets orbit the Sun (not drawn to scale) because it has a massive gravitational pull.The orbits are all ALMOST circular. The shape is called an ellipse.

We know next to almost nothing about the Solar System.

Mercury

VenusEarth

Jupiter

Uranus

Mars

Saturn

Neptune

planets in our solar system

My Very Easy Method Just Speeds Up

Naming

GRAVITY FROM FAR AWAY

The force of gravity between objects gets weaker as their separation increases.

gravity

The moon’s gravity is felt weakly on earth because the moon is so far away and also because the moon is smaller than earth.

However, it is strong enough to move water on the earths surface – our tides!

http://www.youtube.com/watch?v=p_o4aY7xkXg

http://topdocumentaryfilms.com/when-we-left-earth-nasa-missions/

For a rocket to take off from the earths surface it

Must have enough force to overcome the force of gravity.

Rockets can burn up to 13 tonnes of fuel per second which creates enough force to lift the rocket away from the surface.

Answer the questions below in sentences.

1. As the rocket gets further away from the surface of the earth what happens to its gravitational pull?

2. What happens to the mass of the astronauts in a rocket as it moves away from the surface of the earth?

3. For space missions leaving the moon, is more or less fuel needed to leave the surface of the moon than from the earth? Why?

• Explain what satellites are and how they are kept in orbit.

• Describe what geostationary satellites and low polar orbit satellites are.

LEARNING OUTCOME

WHY PLANETS ORBIT THE SUN

The suns gravitational force is so strong that it keeps planets moving around it.

Planets orbit the sun because they are

moving and there is a force of gravity.

Is there was no gravity, a moving planet

would speed off into space.

If it wasn’t moving a planet would fall into the sun.

WHAT ARE SATELLITES?

A satellite is the name for a smaller object that orbits a larger one.

Satellites can be natural (the moon is the earths natural satellite and planets are the suns satellites) or man made (artificial).

Satellites can be natural (the moon is the earths natural satellite and planets are the suns satellites) or man made (artificial).

A satellite will only stay on orbit if it is moving at the right speed for the gravitational pull it feels.

Satellites further away must travel more slowly than closer satellites.

The time it takes any planet to orbit the sun is its year. Planets further away from the sun have longer years.

ARTIFICIAL SATELLITES

Sputnik

The Russians launched the first satellite,

Sputnik in 1957.

Now artificial satellites have many different uses and may be manned or stay permanently in space. They are powered using solar panels, and have insulating blankets on their cold side.

DIFFERENT TYPES OF ORBIT

Geostationary Orbit

•Stays at the same point above earth all the time

•Moves around the equator

•Takes 24 hours to complete its orbit

Using Geostationary satellites

•Communicate with the same point

•Examples include:

•High speed phone links

•Satellite TV

•Computer links

•High speed phone links

Low Polar Orbit

•Can circle the earth in 90 minutes

•Can scan the whole earths surface several times in a day.

Using Low polar orbit satellites

•Produce computer images

•Weather reports and imaging

•Study crops and forests

•Animal migrations

•Look for oil / water reservoirs

GPS SATELLITES

(Global Positioning System)

Satellites can be used to find the position of things accurately.The USA created GPS by launching satellites in different orbits, each taking 12 hours to orbit the earth. It is accurate to 3metres.

GPS UsesNavigationSurveyingEmergency vehiclesApplying pesticides / fertilizer

HUBBLE

Large satellites can takle photographs of the nearby galaxy and can study the sun in more detail. Since the orbit is outside the earths atmosphere the photographs are much clearer then ones from land based telescopes.

The Hubble space telescope was launched in 1990 and since then has produced very detailed photographs of distant stars.

hubbles universe

• http://topdocumentaryfilms.com/the-planets/

• http://www.youtube.com/watch?v=WkuxGwKqx5U

• http://www.youtube.com/watch?v=YY579YpDTws&feature=related

• http://www.youtube.com/watch?v=euOubv2OlPA&feature=related

• Describe early scientific theories on space.

LEARNING OUTCOME

• State whether two objects of the same mass will reach the ground at the same time when dropped.

• Explain this phenomenon.

LEARNING OUTCOME

FEATHER_VS_PENNY_FALLING.WMV

http://www.youtube.com/watch?v=aCTHVhCQSQs

http://www.youtube.com/watch?v=0iDyhg0BPZA

http://www.youtube.com/watch?v=NOqR1Csv7yg&feature=BFa&list=SPDE65D78966FEC465&lf=list_related

2 objects when dropped from the same height will have hit the ground at the exact same time regardless of the mass of the object.

The only other force acting on the objects will be due to air resistance.