GCSE Level Understanding of our place in the Universe
By the end of the GCSE you should have a good basic grasp of our place in the Universe.
All of the KS3
material you studied in Y7 is assumed to be known and understood! I suggest you start
there and then move on. You came across 'bits' of this information in the first two modules - but by the end of module 3 all of this should be clear to you. Here are some links that should jog your memory.
Early man tried to explain his known
universe in religion and folk tales. Now we rely on science to explain
it. Our understanding of the Universe is an on going process that
involves observations, then calculations on them leading to development
of a theory and a model that produces predictions. These can then
be checked by looking for evidence that the predictions are correct,
supporting the theory that generated them and indicating our model
is good.
This has been the case since early times (eg. flat earth/round
earth controversy). The theories we hold now could easily be displaced
by better ones in the future as our ability to make observations and
analyse them (because of the computer) improves.
Our Earth is one of eight planets
(Pluto has recently been demoted to a minor planet) that orbit a rather unremarkable star called Sol.
The Moon is a natural satellite that orbits our Earth.
Other planets may have their own moons.
Stars are the only heavenly bodies that give out their own light - all others are seen by light from stars reflected off the surface. Sol (our Sun) is one of millions
of stars that make up the Milky Way (our galaxy) and may have
planetary systems. Some stars share systems and orbit around a point
between them (binary star systems). The stars tend to group
together in clusters within the galaxy. Galaxies of stars group
together in clusters, and these clusters form even bigger clusters
within the whole Universe (i.e. mass is not distributed evenly
but in lumps!). The force that is pulling these masses together is
called gravity.
Gravity is responsible for the
pull of the moon on the Earth's oceans resulting in tides (Spring
and neap tides etc. - see text book). Gravity is a force of
attraction betweenall masses.
The gravitational force
of attraction between two masses (m1 and m2)is proportional to the
product of the two masses involved and inversely proportional
to the square of the distance between them (r) (the bigger the
masses, the bigger the pull - the further away they are, the less
the pull).
On Earth the principal force of gravity it due to the attraction
of objects to the Earth itself. This is so much bigger than all other
pulls of gravity that theothers can be ignored and masses are pulled towards
the centre of the Earth. In the Solar system it is the Sun that is
the major massive body... so everything gets pulled into an orbit around it (unless it is closer to a planet and then it becomes a satellite of that rather than orbiting the star (Sol)..
The temperature rise resulting from
a given absorption of heat energy (or temperature fall resulting from
the emission of the energy) varies from substance to substance. The
quantity of energy that can be absorbed by one kilogram of a substance
resulting in a temperature rise of one degree kelvin is called itsspecific heat capacity.
You should be able to recall:
Theplanets in the Solar System
in order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn,
Uranus, Neptune, (Pluto (Pluto has an eccentric orbit which means sometimes
it is closer to the Sun than Neptune and has now been demoted - but may still crop up in questions)).
A scalar
property has magnitude (size) only. Eg. mass, speed, distance. energy
of all types, temperature whereas avector property
has magnitude (size) and direction. The direction is indicated by
an arrow the length of which indicates the magnitude of the force.
Eg. force, weight, velocity, acceleration, displacement.
Inertia is the resistance
of an object to change its velocity (speed and/or direction). The
more mass a body has the greater its inertia.
A force is that which
changes (makes it go faster, slower and/or change direction), or tends
to change (if the object has too much mass - this often results in
a deformation of the object) the state of rest or motion of a body.
It is a push or a pull and is measured in newton (N). It is a vector.
If a net force is acting on a body it will accelerate [F=ma]. If no
net force acts the body continues at constant velocity (steady speed
in a straight line).
A driving force
pushes an object in the same direction as it is travelling - increases
velocity whereas acounter force pushes the object in
the opposite direction to that it is travelling in - decreases velocity.
Eg. friction, air resistance (both of these increase with speed).
Terminal velocity is
reached when the sum of the counter forces = the sum of the driving
forces. No net force acts so the body continues at constant velocity
(steady speed in a straight line).
Gravity holds moons in orbit
around planets and planets in orbit around stars. Orbits are elliptical
(oval shaped!) but most of the planets in the solar system (except
Pluto) have virtually circular orbits. There is a pull between the
planets themselves as well as the planets and the Sun. This results
in the orbits of the planets being virtually on a plane with one another.
Planets near to the Sun are basically
composed of rocky materials (very dense) but those further away
from the Sun are composed of ice and rock (less dense).
Planets near to the Sun have a higher
average temperature than those further away. (NB ~ temperature
and pressure determines which state (solid, liquid or gas) a substance
is in).
The orbital period (time taken
for one orbit of the Sun - its year) gets larger as the planet gets
further from the Sun but its rotational period (time taken
for it to rotate once on its axis - its day) has no such pattern.
Some planets have days that are longer than the year!
The larger the mass of the planet the
bigger its gravitational field strength but the bigger the
square of the radius of the planet the smaller its gravitational field
strength.
Only planets with a large enough mass/radius2
ratio can have an atmosphere. Generally speaking the greater
the gravitational field strength the greater the chance of a dense
atmosphere, but factors such as average surface temperature play a
big part also so this picture is not that simple.
The Universe is vast and very old.
Distances between stars have to be measured in light years. A light
year is the distance light can travel in a year (6 million million
miles). There are many theories to explain how it came to be eg.Big Bang Theory.
We know that the Universe is expanding
(but at a decreasing rate as it cools due to the effect of gravity)
from measurement of the movement of distant galaxies. Just as the
whistle of a train sounds at lower pitch as it passes us and moves
away, so light has its wavelength made appear longer if the source
is moving away (making it shift towards the red end of the spectrum).This is called Red
Shift.
You should be able to:
Describe thelife
cycle of a small to medium star: Nebula (gas) to sun like ours
in the stable stage, to red giant, to white dwarf and finally black
dwarf (NB appreciate the effect of gravity at each stage - pulling masses
together and the fact that nuclear reactions inside the star cause forces
that expand the star. these two are in equilibrium if the star is stable,
gravity wins if the star is shrinking etc.).
Describe the life cycle of a large
star'. Nebula (gas) to sun like ours in the stable stage, to red
giant, to supernova, to neutron star and finally black hole (NB appreciate
the effect of gravity at each stage).
Remember that:
Nuclear fusion must be responsible
for the Sun's energy as chemical energy release (burning) cannot account
for the energy it gives out. Fusion is the joining together of small
nuclei together eg (hydrogen to form helium). This produces a large
amount of energy from a small amount of mass.
HEAT travels from hot to cold
(NOT necessarily up !!). It is a form of energy measured in joule
(J). The thing that determines which way it travels is temperature (measured in degrees kelvin (K), Celcius (°C)].
A body possessesklnetic energy
(J) only if it is moving.
A body gainsgravitational potential
energy (J) as it is moved against a gravitational force (i.e.
vertically up) and loses it as it moves in the same direction as gravity
(down!).
A projectile's velocity must
be considered as vertical velocity (under action of a force - gravity)
and horizontal velocity (at constant velocity in a straight line).
The two vectors must then be added together. The shape of a projectile's
path is parabolic.
An object will only move in a circle
if it is constantly being pulled towards the centre of that circle.
This means that an object orbiting at constant speed is accelerating
(change in velocity because direction is changing). It is acting under
a force. The force that acts towards the centre of the circle
is called the centripetal force. If the force were to be removed
the object would fly off at a tangent.
When you are travelling in an orbiting spacecraft
you are accelerating in a circular orbit at constant speed. (NB
acceleration can be due to change in speed and/or direction!!). You are
falling towards Earth and so is the spaceship and all of its contents.
You are only aware of your weight on Earth because the ground pushes up
on you giving a balance of forces so that you don't accelerate. In the
orbiting spaceship this doesn't happen, instead everything is 'falling'
and you feel weightless. (NB You have weight! ~ the Earth is pulling
you - you are just not able to perceive that you have it).
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GCSE Level Understanding of our place in the Universe 
