2. 03/04/2023
Gravity
Gravity is an attractive force that affects anything with mass:
Note that this
force goes both
ways – the Earth
is attracted to us.
3. 03/04/2023
03/04/2023
Weight vs. Mass
Earth’s Gravitational Field Strength is 10N/kg. In other
words, a 1kg mass is pulled downwards by a force of 10N.
W
g
M
Weight = Mass x Gravitational Field Strength
(in N) (in kg) (in N/kg)
1) What is the weight on Earth of a book with mass 2kg?
2) What is the weight on Earth of an apple with mass 100g?
3) Lee weighs 700N on the Earth. What is his mass?
4) On the moon the gravitational field strength is 1.6N/kg.
What will Lee weigh if he stands on the moon?
20N
1N
70kg
112N
4. 03/04/2023
Gravity on different planets and the moon:
Jupiter: g = 25N/Kg
Earth –
gravitational
field strength =
10N/Kg
The moon:
g = 1.6N/Kg
5. 03/04/2023
The eight planets of our Solar System
Mercury
Mars
Jupiter
Saturn
Neptune
Uranus
Venus
Earth
As well as the eight planets, the solar system is also made
up of asteroids, dwarf planets, comets and moons
6. Our understanding of the solar system
03/04/2023
Ptolemy, AD 90-168
Copernicus, 1473-1543
Up until the 16th Century people believed that
the Earth was the centre of the universe – this
is called the “Geocentric model” and I made a
model of the universe based on it.
I published my “On the revolutions of the
celestial spheres” just before my death and
showed that the Earth and other planets orbit
around the sun – the “Heliocentric model”.
7. Evidence for the Heliocentric Model
03/04/2023
Galileo, 1564-1642
Jupiter and its moons, as seen
through a telescope
The orbits of
these moons
I helped develop the modern telescope
and made measurements with it that
proved that the Copernican model of the
solar system was correct.
9. 03/04/2023
Comets
Comets are balls of dust and frozen
gas. They have very elliptical orbits:
Notice how the tail always points away from the sun!
10. 03/04/2023
The Solar System summarised
What makes up our solar system? Complete the following mind
map with what you now about each object:
The solar system
13. 03/04/2023
The Moon’s Orbit
Gravity also keeps the moon (a natural satellite) in orbit
around us. How long does this take?
Does the moon
travel at constant
speed?
Does it travel at
constant velocity?
14. 03/04/2023
Satellite orbits
Gravity also keeps artificial satellites in orbit around us.
Q. What would have to
happen to the satellite’s
speed if it moved closer
to the Earth?
A. As the orbital radius
INCREASES the speed
of the satellite will
DECREASE.
15. Stephen Hawking
03/04/2023
The formation of the
universe
The “Steady State” theory
This theory states that the universe has always existed as it does now and
hasn’t changed. The trouble is that the night sky would be completely lit
up because of the billions of stars, but it’s not, so…
The “Big Bang” theory
This theory states that the universe started off with an explosion and
everything has been moving away ever since. There are two main pieces of
evidence for this: background microwave radiation and red shift.
There are two main theories about how
the universe started:
16. 03/04/2023
How did the universe begin?
The Big Bang Theory suggests that the universe began from a
very small region that was very hot and dense, and then…
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If you pass the light through a gas something
different is seen…
helium
Some wavelengths of light
are absorbed by the gas –
an “absorption spectrum”.
21. 03/04/2023
The absorption lines have all been “shifted”
towards the longer wavelength end (red end)…
After
Before
A similar effect happens with sound –
this is called “The Doppler Effect”
This is called red
shift. The faster
the light source
moves the further
its light will be
“shifted”
22. 03/04/2023
Red Shift simplified
Basically, if I walk towards you I’ll look
slightly more blue. Then, if I walk away
from you, I’ll look slightly more red!!
Let’s try it…
25. 03/04/2023
Light from different stars and from the edge
of the universe also shows this “red-shift”.
This suggests that everything in the universe
is moving away from a single point.
This is the BIG
BANG theory
26. 03/04/2023
Red shift summary
Light from other galaxies has a longer _________ than expected. This
shows that these galaxies are moving ____ from us very quickly. This
effect is seen to a greater extent in galaxies that are _______ away from
us. This indicates that the further away the galaxy is, the ______ it is
moving.
Words to use – faster, away, big bang,
billion, wavelength, further, supernovae
This evidence seems to suggest
that everything in the universe is
moving away from a single point, and
that this process started around 14
_____ years ago. This is the ____
________ Theory. Observations
of ________ from 1998 onwards
have suggested that distant
galaxies are receding even faster.
27. Cosmic Microwave Background Radiation
03/04/2023
Further evidence of the Big Bang theory is Cosmic Microwave
Background Radiation (CMBR) – this radiation comes from the
Big Bang and fills the _________.
Basically, at the start of the
universe, radiation was hot and
had high _______. As time went
on the ________and energy of
this radiation dropped which
turned it into ________. This
“background microwave _______”
is all over the universe.
Words – microwaves, frequency, temperature, universe,
radiation
28. Big Bang Theory vs Steady State
03/04/2023
Some scientists have explained that red shift can actually be used to
support the Steady State Theory As red shift may be a result of matter
being created in spaces as the universe expands and contracts.
Stephen Hawking, 1942 -
However, the discovery of
CMBR was the final nail in the
coffin for the Steady State
theory. So, the Big Bang
theory is now the widely
accepted theory of how the
universe began as there is
more evidence for it.
35. 03/04/2023
Gravity will slowly pull these
particles together…
As they move inwards
their gravitational
potential energy is
converted into heat and
a PROTOSTAR is formed
Stage 2: Protostar
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Stage 3: Main Sequence
Our sun is an example of a main sequence star –
it’s in the middle of a 10 billion year life span
In a main sequence star the forces
of attraction pulling the particles
inwards are _________ by thermal
expansion forces due to nuclear
______ reactions and the high
temperature.
Stars are basically ________ reactors that use _______ as a
fuel. During its main sequence a star will release energy by
converting hydrogen and helium (light elements) into
_________ elements and this is why the universe now
contains a number of heavier elements.
Words – heavier, balanced, hydrogen, nuclear, fusion
37. 03/04/2023
Eventually the hydrogen and helium will run out. When
this happens the star will become colder and redder and
start to swell…
If the star is relatively small
(like our sun) the star will
become a RED GIANT
If the star is big (at
least 4 times the size of
our sun) it will become a
RED SUPERGIANT
Stage 4: Red Giant
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What happens at this point depends on the size of the star…
1) For SMALL stars the red giant will collapse under its own
gravity and form a very dense white dwarf:
Stage 5: The Death
White dwarf Black dwarf
Red giant
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2) If the star was a RED
SUPERGIANT it will shrink and
then EXPLODE, releasing massive
amounts of energy, dust and gas.
After
Before
This explosion is
called a
SUPERNOVA
Stage 5: The Death
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The dust and gas on the outside
of the supernova are thrown
away by the explosion and the
remaining core turns into a
NEUTRON STAR.
If the star is big
enough it could
become a BLACK
HOLE instead.
Stage 5: The Death
41. 03/04/2023
The dust and gas thrown out by a supernova can be used to
form a new star…
Stage 6: Second generation stars
Our sun is believed to be a “______ ______ star” – this is
because it contains some __________ elements along with
hydrogen and ________. These heavier elements would have
been produced by a ____________ and thrown out when the
star exploded. These heavier elements are also found on
planets, indicating that they might have been made from
remains of previous _______ as well.
Words – helium, heavier, second generation, stars, supernova
42. 03/04/2023
The Life Cycle of a Star summary
Protostar
Main sequence
Red super giant
Supernova
Red giant
White dwarf
Black dwarf Neutron star Black hole
Basically, it all depends on the size of
the star!
SMALL
stars
BIG
stars
44. 03/04/2023
Observing the Universe
Consider different types of telescope:
Ground-based telescopes Space-based telescopes
What are the advantages and disadvantages of each?
45. 03/04/2023
Benefits of observing above the atmosphere
Clearly, ground-based telescopes are a problem because of a
number of things:
•The amount of _____ absorbed by
the __________
• Bad _______
• Light is refracted, diffracted and
_______ by the atmosphere
(causing stars to “twinkle”)
• Light ______from nearby cities
The solution is to put telescopes in space or build them high
up on a mountain.
Words – pollution, weather, light, atmosphere, scattered
