Transcript Nat 4 5 Dynamics Space

Signals from Space
We live on a planet called Earth, this is a big
lump of rock that orbits the sun. There are 7 other
planets orbiting the sun. They make up the solar
system along with the moons , asteroids and
dwarf planets.
Signals from Space
The sun is a star, it is our source of heat and light
energy.
Our sun is one of millions of stars that make up the
Milky Way galaxy ( a group of stars ).
The milky way galaxy is one of
millions of galaxies that make
up the universe. Exoplanets orbit stars
In other solar systems.
Electromagnetic Spectrum
This is a group of radiations ( waves ) that
travel at 3 x 108 ms-1 through air / vacuum.
They are grouped according to their
frequency / wavelength , have different
properties and are detected by different
detectors.
The different signals convey different types
of information e.g. search for ET life uses
radio waves but black holes can be
detected by searching for gamma rays.
Electromagnetic Spectrum
Remember that v  f x 
Radiation
TV and Radio
Microwaves
Infrared
Visible Light
Ultra Violet
X Rays
Gamma rays
Detector
Aerial
Aerial
Photodiode/ (hand)
Eye
Fluorescence of
chemicals
Photographic film
Geiger Muller tube
Increasing
frequency
Electromagnetic Spectrum
Calculate the frequency of 300 m radio
waves. Remember that all members of the
electromagnetic radiation travel at
3 x 108ms-1.
V = 3x108 ms-1 λ = 300 m f = ?
v  f x
 f
v

8
3 x 10
6

 1 x 10 Hz
300
Light Year
This is the distance that light would travel
in one year:
Distance = speed x time
d  v x t  3.0 x10 x 365 x 24 x 60 x 60  9.46 x10 m
8
( this is equivalent to going around the
earth 250 million times )
15
moon
Light Year
Time for
Distance
light to
(m)
travel from
earth
1.2 seconds
sun
8 minutes
Object
Next nearest 4.7 years
star
Edge of
100 000
Milky Way years
Galaxy
Telescopes
Used to gather signals from distant
objects ( signals can be any member of
electromagnetic spectrum ):
Spectroscopy
White light can be split into its spectrum by a
prism. The shorter the wavelength of light the
more refraction and bending of the light.
Blue λ = 450 nm
Green λ = 550 nm
Red λ = 650 nm
Red
Green
Blue
Continuous spectrum
• All colours merge into each other , like a rainbow.
• Hot objects emit a continuous spectrum
• Temperature of star can be calculated by looking
at spectrum
• Cool objects emit red light but as the temp
increases , red, green and blue light are emitted :it
glows white
Line Spectrum
•
•
•
•
Emitted by low pressure gases
Chemical composition of stars can be evaluated
Each element has its unique spectrum
These are called emission spectrum
The Big Bang
Big Bang theory states approximately 13.7 billion years
ago the universe came into existence . It started as a
single point and a rapid expansion occurred. Initially the
temperature was very hot and only ‘energy existed’.
As it expanded , it cooled and ‘matter’ was formed .
Initially particles called quarks and electrons were
formed then eventually protons and neutrons. The
simplest elements then followed : Hydrogen then
helium.
Big Bang : The Evidence
Other galaxies are moving away from us , this suggests
that at one time all the ‘matter’ in the universe must
have been at a single point. This time was approximately
13.7 billion years ago.
Cosmic Microwave background radiation is detected
coming from all directions : This is the remnants of the
‘Big Bang’. ( Initially the temperature was very hot but
it has cooled over time , we have seen that different
temperature objects have different spectra. )
Advantages of Space Exploration
Apart from allowing us to better understand ‘where
we come from’ Space Exploration has had a huge
impact on society :
Use of satellites to predict weather/ storms/GPS
Use of sensors to monitor volcanoes/ investigate the
body
Use of new materials in insulation/ replacement body
parts/ scratch resistant lenses
Improvements in computing…………
Projectile Motion
This has two components : a constant horizontal
velocity and a
vertical velocity that accelerates uniformly at 9.8 m s-2.
Horizontal velocity remains constant if we ignore
frictional forces and spin.
Vertical velocity changes uniformly as gravitational
force acts on object.
This results in a curved
trajectory :
Projectile motion
Example
20 ms-1
Height of cliff,
h,
Now that’s what
I call a speed
bump.
Range,s,
Calculate the horizontal distance ,s , traveled
( range )and the height , h , of the cliff if the car takes
5 s to hit the ground.
velocity time graph
velocity ( ms-1 )
60
50
40
30
20
10
0
0
1
2
3
4
5
6
time(s)
Area under graph = ½ b x h = ½ x 5 x 49 = 122.5 m
Calculate the resultant velocity of the car as it hits the
sea :
Draw a vector diagram:
20 ms-1
Ɵ
49 ms-1
Use Pythagoras to work out hypotenuse
52.9 ms-1
Use trig to work out angle , Ɵ
67.80
Resultant velocity is 52.9 ms-1 , 67.80 below the
horizontal.
Newton’s Thought Expt
The ball is fired
horizontally but
gravitational force
accelerates it towards the
earth. It crashes at point A
If the horizontal velocity is
increased it can ‘reach ‘ a
little further around the
earth to B.
If the horizontal velocity is
increased further it can
travel right round the
earth.
Newton’s Thought Expt 3
If the horizontal velocity of the ball is increased
further it flies off into space.
The ball orbits the earth because gravitational force
is pulling it towards the centre. The ball wants to
travel in a straight line but gravitational force pulls it
inwards.
This is why satellites , natural and man made, orbit
planets.
Re entry
When the space shuttle re enters the earth’s atmosphere
there are huge frictional forces acting against it.
Some of the shuttle’s kinetic energy is turned into heat
energy.
To stop the craft becoming too hot inside, the underside is
painted black, this is a good emitter of infra red radiation.
The underside is also covered with tiles that have a low
specific heat capacity and a low thermal conductivity. This
ensures that the temperature of the tiles rises quickly( but
accordingly lots of heat is radiated to the surroundings )
and a small amount of heat energy is transferred into the
cabin.
Example energy change
The space shuttle, 100 tonnes, slows down from 7 500
ms-1 to 750 m s-1 when it hits the earth’s atmosphere.
Assume that all this change in kinetic energy is turned
into heat energy Calculate the maximum temperature
rise if the specific heat capacity of the thermal tiles,
2000kg, is 50 J kg-10C-1.
Example
Use Ek = 0.5mv2 to calculate kinetic energy
change.
Ek before = 2.8125 x 1012
Ek after = 2.8125 x 1010
Ek change = 2.78 x1012 J
Use Eh = Ek = cm  T
Eh
T 
c xm

2.78 x 1012
50 x 2000
 2.78 x 107 0C
Obviously a lot of the heat energy is re radiated otherwise the
shuttle would melt.
Ablative Heat Shields
When a material turns from a solid to a liquid
or from a liquid to a gas energy is required.
When water evaporates off your skin you cool
down. This idea is used to cool down some
space craft on re entry.
Part of the heat shield is designed to burn away,
the gases produced carry some heat energy
away , cooling the spacecraft.
Satellites
There are two main groups of satellites : geostationary and
polar orbiting.
Polar orbiting satellites orbit over the poles hence they will
‘see’ all parts of the earth over a period of time.
They orbit as low as 1000 km with a
period of 100 mins . The 24 GPS
Satellites orbit at a height of
19,200 km with a period of 12 hrs.
Satellites can be used to gather info
for weather forecasting, ‘spying’,
Monitoring sea levels, temperatures…
Geostationary satellites
They orbit, 36,000 km above
the equator with a period of
24 hrs. They appear above
the same point on earth and
so are used chiefly for
communications. 3 satellites
can be used to send signals
around the entire earth.
Parabolic Reflectors
Signals are gathered over a large area and reflected to a
focus. This increases the strength of the signal. The
microphone is situated at the focus.
Parabolic Reflectors
If a transmitter is situated
at the focus the energy is
transmitted as a parallel
beam. This allows SKY
to direct signals to
specific parts of europe.
Car headlamps use
similar Physics.