Transcript Space and Gravity

UNIT 9J
Gravity and Space
LEARNING
OUTCOME
• Explain the difference between
mass and weight
• Describe gravity
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 and 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 (N) = Gravitational Field Strength (N/kg) x Mass (kg)
W=gxm
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.
Planet
Mass (kg)
g-value (N/kg)
Mercury
3
Venus
9
Earth
10
Mars
4
Jupiter
26
Saturn
11
Uranus
11
Neptune
12
Pluto
0.5
Weight (N)
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!
Space shuttle
- smaller mass
Force of gravity
The force of gravity depends on the
mass of the planet and how close you are
to it.
Earth - large mass
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
The force of gravity between an
Apple and earth is large because
Earth has a very high mass.
Mass = billions of tonnes
LEARNING
OUTCOME
• 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.
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
planets in our
solar system
Earth
Venus
Jupiter
Mars
My Very Easy
Method Just
Speeds Up
Naming
Uranus
Saturn
Neptune
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
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.
http://topdocumentaryfilms.com/when-we-left-earth-nasa-missions/
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?
LEARNING
OUTCOME
• Explain what satellites are and how
they are kept in orbit.
• Describe what geostationary
satellites and low polar orbit
satellites are.
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
The Russians launched the first satellite,
Sputnik in 1957.
Sputnik
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 Uses
Navigation
Surveying
Emergency vehicles
Applying 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/theplanets/
• http://www.youtube.com/watch?v=Wk
uxGwKqx5U
• http://www.youtube.com/watch?v=YY5
79YpDTws&feature=related
• http://www.youtube.com/watch?v=euO
ubv2OlPA&feature=related
LEARNING
OUTCOME
• 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.
FEATHER_VS_
PENNY_FALLI
NG.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.