P16: Space

Question 1

How did the solar system form?

Answer 1

It formed from gas and dust clouds that gradually became more and more concentrated because of gravitational attraction.

Question 2

What are the characteristics of a main sequence star?

Answer 2

• Main sequence stars such as the Sun radiate energy because of hydrogen fusion in the core.
• Energy released in the core keeps the core hot so the process of fusion continues and radiation flows steadily from the core.
• A star is stable because the force of gravity acting inwards is in equilibrium with the outward force of radiation from nuclear fusion in the core.

Question 3

How is a star formed?

Answer 3

1. Starts with massive clouds of dust and gas in space.
2. These clouds of dust and gas are pulled together by gravitational attraction.
3. These clouds join, becoming more and more concentrated, forming a protostar.
4. As the protostar becomes denser it gets hotter and this energy causes lighter nuclei to join together. Energy is released from this fusion reaction so the protostar gets even hotter.
5. It gets hotter and brighter so begins to shine, forming a star.
6. The outward force from pressure of expanding hot gas is balanced by the force of star’s gravity.

Question 4

How does the main sequence stage of a star end?

Answer 4

When a star runs out of hydrogen nuclei to fuse together in its core, the core collapses and it is the end of its main sequence stage.

Question 5

What happens to stars similar size to the sun after the main sequence stage?

Answer 5

• They swell out, cool down and turn into a red giant.
• When there are no more light elements in the core, fusion stops and no more radiation is released.
• The gravity causes the star to collapse, heat up and turn into a white dwarf.
• They then go cold and become black dwarfs.

Question 6

What happens to stars bigger than the sun after the main sequence stage?

Answer 6

• Stars swell out to become red supergiants then collapse.
• During the collapse, the matter surrounding the star’s core compress it more and more.
• This compression causes an explosion called a supernova.
• The explosion compresses the core of the star into a neutron star and if it is massive enough it becomes a black hole.

Question 7

What is the main feature of a black hole?

Answer 7

Its gravitational field is so strong that nothing can escape from it.

Question 8

What is the path of stars similar size to the sun?

Answer 8

Protostar —> Main Sequence Star —> Red Giant —> White Dwarf —> Black Dwarf

Question 9

What is the path of massive stars bigger than the sun?

Answer 9

Protostar —> Main Sequence Star —> Red Supergiant —> Supernova —> Neutron Star or Black Hole

Question 10

How are elements formed?

Answer 10

• Light elements are formed from fusion of hydrogen and helium nuclei in stars.
• Nuclei larger than iron cannot be formed by this process as too much energy is needed.
• Heavy elements are formed in supernova debris. This debris can form new stars or planets.

Question 11

What are satellites?

Answer 11

They are anything that orbits a celestial body and can be both natural or artificial.
Can be used for communication, navigation, weather forecasting and to study earth/universe.

Question 12

What is the centripetal force?

Answer 12

The force on the orbiting body that is the force of gravitational attraction between it and the larger body.

Question 13

How does the centripetal force affect a planet’s motion?

Answer 13

The direction of a planet’s velocity is changed by it, causing it to accelerate towards centre of a circular orbit. Magnitude of velocity does not change.
The direction of motion of any planet in a circular orbit is at right angles to the direction of the force of gravity on it.

Question 14

What is the effect of the force of gravity on an orbiting body?

Answer 14

• The force of gravity between planet/sun and a satellite/earth keeps the satellite or planet to continue moving along its orbit.
• The force of gravity on an orbiting body in a circular orbit is towards the centre of the circle.
• To stay in orbit at a particular distance, a small body must move at a particular speed around a larger body.

Question 15

What is red shift?

Answer 15

• The red shift of a distant galaxy is a shift to longer wavelengths and lower frequencies of light from a galaxy moving away from you.
• If the light waves are stretched then the star or galaxy is moving away from you and the wavelengths increase.
• The greater the red shift, the faster the galaxy is moving away from you and the further is away from you.

Question 16

What is the Big Bang?

Answer 16

It is how the universe started which was a massive explosion from a very small point and the universe has been expanding since.

Question 17

What is cosmic background radiation?

Answer 17

When the universe was young, everything would have been very hot so would have emitted lots of short wavelength radiation. This radiation would have stretched to become microwaves as the universe expanded over time. This background radiation is always present which proves the universe has cooled and expanded since the big bang.

Question 18

What are the two types of orbit models?

Answer 18

Heliocentric: everything in solar system orbits around the sun.
Geocentric: everything in solar system orbits around earth.