Solar System, Stability of Orbital Motions & Satellites (AQA GCSE Physics): Flashcards
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- FrontThe Solar System
Define dwarf planet.
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Define dwarf planet.
A dwarf planet orbits the Sun, but its gravitational field is not strong enough to have pulled in nearby objects.
What are the four rocky planets in the Solar System?
Mercury, Venus, Earth and Mars.
What are the four gas planets in the Solar System?
Jupiter, Saturn, Uranus and Neptune.
Define asteroid.
An asteroid is a small rocky object which orbits the Sun. Most asteroids are found in the asteroid belt between Mars and Jupiter.
What are comets made of, and how does a comet's tail form?
Comets are made of dust and ice. As a comet approaches the Sun, the ice vaporises, forming the comet's tail.
The nearest star to the Sun is so far away that light from it takes ______ to reach us.
The nearest star to the Sun is so far away that light from it takes 4 years to reach us.
True or False?
Light from the Sun takes 8 minutes to reach Earth.
True.
This is because of the vast distance between the Sun and Earth, combined with the finite speed of light (3 × 108 m/s).
Where does our Solar System fit within the wider Universe?
Our Solar System is one small part of the Milky Way galaxy, which contains billions of stars. The Universe is made up of many different galaxies.
What percentage of the Solar System's mass does the Sun make up?
Over 99%.
Define nebula.
A nebula is a giant cloud of dust and gas (mainly hydrogen) from which stars form.
What is the Sun mostly made up of?
Hydrogen and helium.
What are the three initial stages of a star's life cycle, common to all stars?
Nebula → protostar → main sequence star.
Define protostar.
A protostar is a hot ball of gas formed when gravitational attraction pulls the particles of a nebula closer together.
Why does the temperature of a protostar increase as it forms?
As particles are pulled closer together, the density increases, causing more frequent collisions between particles.
What happens once a protostar becomes hot enough, and what is the resulting star called?
Nuclear fusion reactions begin in its core, fusing hydrogen nuclei into helium nuclei. The star is then known as a main sequence star.
A main sequence star is stable because the ______ force due to gravitational collapse is equal to the ______ force due to fusion energy.
A main sequence star is stable because the inward force due to gravitational collapse is equal to the outward force due to fusion energy.
True or False?
If the temperature of a main sequence star increases, the star will contract.
False.
An increase in temperature increases the outward pressure, causing the star to expand instead.
What are the three evolutionary stages that follow the main sequence for a solar mass star, such as the Sun?
Red giant → white dwarf → black dwarf.
Why does a main sequence star like the Sun become a red giant?
As hydrogen fuel runs out, the rate of fusion decreases, causing the core to shrink and heat up. The star becomes a red giant once the core is hot enough for helium to fuse into heavier elements, such as carbon and oxygen.
Define white dwarf.
A white dwarf is the collapsed remnant of a red giant's core, formed once helium fusion can no longer continue. It cools and emits less energy over time.
What happens to a white dwarf as it continues to cool?
It loses a significant amount of energy and becomes a black dwarf, eventually disappearing from sight.
As a red giant forms, the outer layers of the star ______ and ______.
As a red giant forms, the outer layers of the star expand and cool.
What determines whether a star ends its life cycle as a white/black dwarf, or as a neutron star/black hole?
The star's size. This determines the final stages of its life cycle after the main sequence.
True or False?
All stars, regardless of size, begin their life cycle in the same way.
True.
All stars start as a nebula, then become a protostar, then a main sequence star, before their paths diverge based on size.
What are the three evolutionary stages a larger star goes through after the main sequence?
Red supergiant → supernova → neutron star or black hole.
Why does a large star expand and cool to become a red supergiant?
As hydrogen runs out, fusion reactions in the core die down. The star fuses helium into carbon, then further reactions form nitrogen, oxygen and heavier elements up to iron. This causes the outer part of the star to expand while its surface cools.
Define supernova.
A supernova is a gigantic explosion that occurs when the core of a red supergiant collapses suddenly and its outer layers are blown away.
What happens to the material ejected during a supernova?
It forms new clouds of dust and gas (nebulae), which may go on to form new stars with orbiting planets.
Elements heavier than ______ are formed during a supernova explosion.
Elements heavier than iron are formed during a supernova explosion.
Define black hole.
A black hole is an extremely dense object with a gravitational pull so strong that not even light can escape from it.
True or False?
Every neutron star formed in a supernova will go on to become a black hole.
False.
Only in the most massive stars does the neutron star continue to collapse under gravity to form a black hole.
Define nuclear fusion.
Nuclear fusion occurs when two light nuclei collide at high speed and join to create a larger, heavier nucleus, releasing energy as heat and light.
Which element was the only one present when the Universe first formed, 13.8 billion years ago?
Hydrogen.
Where have all the naturally occurring elements, apart from hydrogen, been formed?
They have been formed by nuclear fusion in stars.
How are elements heavier than iron produced?
They are produced in supernova explosions, which provide the extreme conditions needed to fuse elements heavier than iron.
Elements ______ than iron are formed in fusion reactions during a star's lifetime.
Elements lighter than iron are formed in fusion reactions during a star's lifetime.
What evidence suggests that Earth formed from the remains of one or more supernovae?
Earth contains many heavy elements, including some heavier than iron, which can only be produced in a supernova explosion.
True or False?
During nuclear fusion, whole atoms combine to form a new element.
False.
It is only the nuclei that combine during nuclear fusion, not whole atoms.
What provides the force that keeps an orbiting body moving in a circular path?
Gravity, which acts as an attractive force towards the centre of the larger body being orbited.
Why is an object in a circular orbit constantly accelerating, even though its speed is constant?
Its direction is constantly changing, which means its velocity is constantly changing. A change in velocity is an acceleration.
How does the distance of a moon from its planet affect its orbit?
The closer the moon is to the planet, the shorter the time it takes to orbit and the greater its speed.
If the speed of an artificial satellite is too large, the radius of its orbit will ______.
If the speed of an artificial satellite is too large, the radius of its orbit will increase.
If an artificial satellite moves to an orbit with a larger radius, what happens to the force of gravity, orbital speed and orbital period?
The force of gravity decreases, the orbital speed decreases and the orbital period increases.
True or False?
Moving a satellite to a smaller orbital radius increases its orbital speed.
True.
At a smaller radius, the force of gravity increases, which increases the orbital speed and decreases the orbital period.
Where in its orbit is a comet travelling fastest, and where is it travelling slowest?
A comet travels fastest near the Sun and slowest at the point furthest from the Sun.
Explain, in terms of energy, why a comet speeds up as it approaches the Sun.
As the comet approaches the Sun, it loses gravitational potential energy and gains kinetic energy, causing it to speed up.
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