GCSE Physics- Space (check to see if more needs to be added)

What is at the centre of the solar system

The sun

What is the sun

The Sun is a star which makes up over 99% of the mass of the solar system

What orbits the sun

There are 8 planets and an unknown number of dwarf planets which orbit the Sun. Asteroids and comets also orbit the sun

What does the gravitational field strength around planets do

The gravitational field around planets is strong enough to have pulled in all nearby objects with the exception of natural satellites. The gravitational field around a dwarf planet is not strong enough to have pulled in nearby objects

Define orbit

Path on which one object moves around another

Define satellites

An object which orbits a second

What are the rocky planets

Mercury Venus Earth and Mars

What are the gaseous planets

Jupiter, Saturn, Uranus, Neptune

Give an example of a natural satellite

Moons

What are artificial satellites

Artificial satellites are man-made and can orbit any object in space

Give an example of an artificial satellite

The International Space Station (ISS) orbits the Earth and is an example of an artificial satellite

What is an asteroid

An asteroid is a small rocky object which orbits the Sun

Where is the asteroid belt found

The asteroid belt lies between Mars and Jupiter

What are comets

Comets are made of dust and ice and orbit the Sun in a different orbit to those of planets. The ice melts when the comet approaches the Sun and forms the comet’s tail

What is the mnemonic for remembering the order of the planets

My Very Excellent Mother Just Served Us Noodles

What is the order of the planets in the solar system

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

What is a galaxy

A collection of billions of stars and their solar systems

What is the universe made up of

Different galaxies

How are the planets and moons of the solar system visible from Earth

When they reflect light from the Sun

How long does it take light from the Sun to reach Earth

The light we receive on Earth from the Sun takes 8 minutes to reach us

Where is the nearest star to us after the Sun

The nearest star to us after the Sun is so far away that light from it takes 4 years to reach us. The Milky Way galaxy contains billions of stars

What is the speed of light

3 × 10⁸ m/s

What is the sun made up of

It consists mostly of two elements hydrogen and helium

How did the sun and the other planets in the Solar System form

The Sun and all the planets in the Solar System formed from a massive cloud of dust and gas called a nebula. Gravitational attraction pulled this cloud together into a giant ball. As the nebula collapsed the centre of this ball got very dense and hot and began to rotate. This hot dense ball was the Sun as a protostar. Eventually when the Sun's core became hot enough hydrogen nuclei started to undergo nuclear fusion to form helium nuclei

What is a nebula

A nebula is a cloud of gas and dust in space

What is the star formation

nebula → protostar → main sequence star

How do stars form

Stars form from a giant cloud of hydrogen gas and dust called a nebula

How does a protostar form

The gravitational attraction within a nebula pulls the particles closer together until a hot ball of gas forms known as a protostar. As the particles are pulled closer together the density of the protostar increases. This results in more frequent collisions between the particles which causes the temperature to increase.

How does a main sequence star form?

Once the protostar becomes hot enough nuclear fusion reactions occur within its core. The hydrogen nuclei will fuse to form helium nuclei. Every fusion reaction releases heat (and light) energy which keeps the core of the star hot. Once a star initiates fusion it is known as a main sequence star. The star will remain stable in this stage for the majority of its life.

Which direction does gravity act?

Gravity acts inwards. This is an attractive force which pulls the outer layers inwards

Which direction does pressure act?

Pressure acts outwards. This arises from an outward force exerted by the expanding hot gases inside the star as a result of energy released by fusion reactions

When is a star in equilibrium?

When the two forces are balanced the star is in equilibrium and it is said to be stable. The inward force due to gravitational collapse is equal to the outward force due to fusion energy.

What happens if the temperature of a star increases?

If the temperature of a star increases the outward pressure will also increase. This occurs when the energy released by fusion reactions increases. This will cause the star to expand.

What happens if the temperature of a star drops?

If the temperature drops the outward pressure will also decrease. This occurs when the energy released by fusion reactions decreases. This will cause the star to contract

What do the final stages of a star's life cycle depend on?

Its size

What stages to stars of similar sizes to the sun go through?

red giant → white dwarf → black dwarf

How are red giants formed?

After several billion years the hydrogen fuel used for nuclear reactions begins to run out. Once this happens the rate of fusion decreases which causes the core to shrink and heat up. As the energy produced by fusion decreases the inward force due to gravity becomes greater than the outward force due to the thermal pressure.

How are white dwarfs formed?

Once the helium in the core begins to run out fusion reactions cannot continue. The star becomes unstable and the core collapses under its own gravity. The remnant of the core is known as a white dwarf. The white dwarf will be cooling down

How are black dwarfs formed?

Once the star has lost a significant amount of energy it becomes a black dwarf. It will continue to cool until it eventually disappears from sight

What stages do larger stars undergo?

red supergiant → supernova → neutron star or black hole

How do red supergiants form?

After several million years the hydrogen that fuels the fusion reactions in the star will begin to run out. Once this happens the fusion reactions in the core will start to die down. The star will begin to fuse helium to form carbon. This is followed by further fusion reactions in which nitrogen and oxygen are formed. Heavier elements up to iron are also formed. This causes the outer part of the star to expand. As the star expands its surface cools and it becomes a red supergiant.

How do supernovas form?

Once the fusion reactions inside the red supergiant cannot continue the core of the star will collapse suddenly. The outer layers are blown away in a gigantic explosion. This is called a supernova. At the centre of this explosion

How do neutron stars (black holes) form?

In the case of the most massive stars the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole.

What is a black hole?

A black hole is an extremely dense object which has a gravitational pull so strong that not even light can escape from it.

How are all naturally occurring elements formed?

All the naturally occurring elements apart from hydrogen have been formed by nuclear fusion in stars.

When does nuclear fusion occur?

Nuclear fusion occurs when two light nuclei collide at high speed and join to create a larger heavier nucleus.

When was the universe formed?

13.8 billion years ago

What was the only element present when the universe first formed?

Hydrogen

What happens if two hydrogen nuclei collide with enough energy?

If two hydrogen nuclei collide with enough energy they will fuse into a helium nucleus. For example the nuclei of two different isotopes of hydrogen (protium and tritium) can join to form a helium nucleus by the process of nuclear fusion.

How are new elements formed?

During the majority of a star’s lifetime hydrogen nuclei fuse together to form helium nuclei. As the star runs out of hydrogen other fusion reactions take place forming the nuclei of other elements.

When are elements lighter than iron formed?

In fusion reactions

When are elements heavier than iron formed?

In supernova explosions

What is a supernova?

A supernova is a bright and powerful explosion that happens at the end of a massive star's life.

When does a supernova occur?

It occurs when the star is bigger than the Sun

What happens during a supernova?

The explosion releases a large amount of energy. During a supernova all of the elements which were produced by the fusion reactions are expelled along with neutrons. The neutrons combine with the elements to form even heavier elements. These elements are ejected into the universe by the supernova explosion and form new planets and stars. Since Earth contains many heavy elements including ones heavier than iron this is proof that it must have formed from the remains of one or more supernovae.

What do planets orbit?

Sun

What do moons orbit?

Planet

What do comets orbit?

Sun

What do asteroids orbit?

Sun

What do artificial satellites orbit?

Any larger body in the Solar System

How do bodies orbit?

A smaller body or object will orbit a larger body. In order to orbit a body such as a star or a planet there has to be a force pulling things towards that body. Gravity provides this force. The gravitational force exerted by the larger body on the orbiting object is always attractive. Therefore the gravitational force always acts towards the centre of the larger body. The gravitational force is the centripetal force as it will cause the body to move and maintain a circular path.

Describe orbits in motion

Planets travel around the Sun in orbits that are (approximately) circular. Objects moving in circular orbits move at a constant speed but their direction is constantly changing. A change in direction indicates a change in velocity and a change in velocity indicates acceleration. Therefore if an object in orbit is constantly changing direction then its velocity is constantly changing and hence

What is needed to cause acceleration?

A resultant force is needed to cause an acceleration

What is this resultant force in this context?

This resultant force is gravity which must act at right angles to the instantaneous velocity of the object to create a circular orbit. This is always towards the centre of the orbit. The instantaneous velocity of the object is the velocity at a given time

What are the similarities in the ways different planets orbit the Sun?

Their orbits are all slightly elliptical (stretched circles) with the Sun at one focus (approximately the centre of the orbit). They all orbit in the same plane. They all travel the same direction around the Sun

What are the differences in the ways different planets orbit the Sun?

They orbit at different distances from the Sun. They orbit at different speeds. They all take different amounts of time to orbit the Sun

How do moons orbit?

Moons will orbit planets in a circular path. Some planets will have more than one moon. The closer the moon is to the planet: the shorter the time it will take to orbit: the greater the speed in the orbit.

How do artificial satellites orbit?

A satellite needs to travel at a specific speed to maintain a circular orbit at a particular distance from the object it is orbiting

If the speed of the satellite is too large:

the radius of the orbit will increase and the satellite will move into a higher orbit further from the object it is orbiting. the satellite may leave the object's gravitational field altogether

If the speed of the satellite is too small:

the radius of the orbit will decrease and the satellite will move into a lower orbit closer to the object it is orbiting. the satellite may spiral inwards towards the object but only if a continuous force acts on it such as atmospheric drag.

How is the speed of an artificial satellite affected by its orbital radius?

If an artificial satellite in a stable orbit is to change the radius at which it is orbiting then its speed must change.

If the satellite is moved further away from the object to an orbit with a larger radius:

the force of gravity decreases. the orbital speed decreases. the orbital period increases

If the satellite is moved closer to the object to an orbit with a smaller radius:.

the force of gravity increases. the orbital speed increases. the orbital period decreases

How are the orbits of comets different to those of planets?

The orbits are highly elliptical (very stretched circles) or hyperbolic. This causes the speed of the comets to change significantly as its distance from the Sun changes. Not all comets orbit in the same plane as the planets and some don’t even orbit in the same direction

Describe the orbital path of a comet

As the comet approaches the Sun it loses gravitational potential energy and gains kinetic energy. This causes the comet to speed up. This increase in speed causes a slingshot effect

What happens when an object emits waves?

Usually when an object emits waves the wavefronts spread out symmetrically. If the wave source moves the waves can become squashed together or stretched out. A moving object will cause the wavelength λ (and frequency) of the waves to change: The wavelength of the waves in front of the source decreases (λ – Δλ) and the frequency increases. The wavelength behind the source increases (λ + Δλ) and the frequency decreases. This effect is known as the Doppler effect

Define the Doppler effect

The change in frequency or wavelength due to the relative motion between a source and an observer

What does the Doppler effect do?

The Doppler effect also affects light. If an object moves towards an observer the wavelength of light decreases. This is known as blueshift as the light moves towards the blue end of the spectrum. If an object moves away from an observer the wavelength of light increases. This is known as redshift as the light moves towards the red end of the spectrum.

Define red shift

The observed increase in the wavelength of light due to the source moving away from the observer.

What does the light spectrum show?

The diagram also shows that the light coming to us from distant galaxies is redshifted

The lines on the spectrum are shifted towards the red end

This indicates that the galaxies are moving away from us. If the galaxies are moving away from us it means that the universe is expanding. The observation of redshift from distant galaxies supports the Big Bang theory. Another observation from looking at the light spectrums produced from distant galaxies is that the greater the distance to the galaxy the greater the redshift. This means that the further away a galaxy the faster it is moving away from us.

Describe the Big Bang Theory

Around 14 billion years ago the universe began from a very small region that was extremely hot and dense. Then there were a series of explosions which we call the Big Bang. This caused the universe to expand cooling as it did so to form the universe we currently observe. Each point expands away from the others. This is seen from galaxies moving away from each other and the further away they are the faster they move. As a result of the initial explosions the universe continues to expand

What is the evidence for the Big Bang?

By observing the light spectrums from supernovae in other galaxies there is evidence to suggest that distant galaxies are receding (moving further apart) ever faster. These observations were first made in 1998. The light spectrums show that light from distant galaxies is redshifted which is evidence that the universe is expanding – the galaxies are moving away from us - and indeed each other. If you were to travel back in time and compare the separation distance of the galaxies they would become closer and closer together until the entire universe was a single point. If the galaxies were originally all grouped together at a single point and were then exploded we would see a similar effect. The galaxies that are moving fastest would move the furthest - the distance they move would be proportional to their speed. The galaxies that are moving slowest would move the least

What happens in an explosion?

Matter is first densely packed and as it explodes it moves out in all directions getting further and further from the source of the explosion. Some matter will be lighter and travel at a greater speed

What are some observations that are still not understood?

Evidence from the rotation and motion of galaxies suggests that there is much more matter in the Universe than we are able to account for. This unseen matter is given the name dark matter and its nature is not currently known

What do measurements of the expansion of the universe show

Measurements of the expansion of the Universe using supernovae suggest that the Universe is starting to expand at a faster rate It has been suggested that this accelerated motion is caused by dark energy pushing everything in the Universe apart