Physics revision test 2

Question 1

Name the eight planets in order

Answer 1

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Question 2

What is the sun

Answer 2

A star

Question 3

Name a natural satellite

Answer 3

Moons

Question 4

Where is the asteroid belt situated?

Answer 4

Between Mars and Jupiter

Question 5

What are comets?

Answer 5

Frozen rocks that move around the Sun, often in very elliptical orbits

Question 6

Where is our solar system?

Answer 6

In the Milky Way Galaxy

Question 7

How was the sun formed?

Answer 7

1) A nebula was pulled together by gravitational attraction
2) The particles in the cloud got faster and collided more
3) The gas warmed up and became hot enough to glow (Protostar)
4) The protostar gets more dense, more collisions take place, and it gets hotter
5) The cloud gets hot enough for Hydrogen atoms to fuse, forming Helium (Main Sequence Star)

Question 8

When was the sun formed?

Answer 8

4.5 billion years ago

Question 9

Why does the sun remain in the Main Sequence stage?

Answer 9

The gravitational attraction still pulling on the gas is balanced by the outward force of the radiation from the nuclear fusion in the core. The forces are in equilibrium

Question 10

Why do we have uranium?

Answer 10

Uranium (and other heavy elements naturally present on earth) can only be formed in a supernova explosion, so the sun must have formed from the remnants of a supernova

Question 11

What will eventually happen to the Sun?

Answer 11

The star runs out of Hydrogen, its core collapses and the outer layers swell, cool and become a Red Giant.
Helium and other elements in the core fuse to form heavier elements. When there are no more light elements in the core, fusion stops and no more radiation is released. The star collapses and becomes a white dwarf. The stars eventually fade out, becoming black dwarfs

Question 12

What would happen if the Sun was much bigger?

Answer 12

Bigger stars become red supergiants, then they collapse. The collapse is more violent and a supernova explosion occurs. Elements that are heavier than Iron can form from fusion.
The explosion compresses the core into a neutron star - an extremely dense object made of only neutrons. If the original star is massive enough, it becomes a black hole.

Question 13

Why can we not see black holes?

Answer 13

The gravitational field of a black hole is so strong nothing can escape from it, not even light

Question 14

What is a planet?

Answer 14

A planet orbits a star, enough gravity to make it spherical and sweeps out its own orbital path of other smaller objects

Question 15

What is a satellite?

Answer 15

A satellite is something that orbits something else

Question 16

What is a moon?

Answer 16

A moon orbits a planet

Question 16

Give an example of a natural satellite:

Answer 16

The moon

Question 17

T/F: There are artificial (man-made) satellites

Answer 17

True

Question 18

What force allows planets and satellites to maintain their circular orbit?

Answer 18

Gravity. It is an example of a centripetal force because it is acting towards the centre of a circle

Question 19

Describe a circular orbit

Answer 19

An object orbits another object at a constant speed. Its direction is constantly changing, so its velocity is changing. Therefore we say an object is accelerating towards the centre of the circle.

Question 20

What is acceleration?

Answer 20

Change of velocity per second

Question 21

What happens to the orbit of an object if its speed changes?

Answer 21

If an object in orbit slows down, it will fall into a lower orbit. If it gets too slow, it will crash to the surface.
If an object in orbit speeds up, it will move to a higher orbit. If it gets sufficiently fast, it will escape the gravitational pull of the object and fly off into space.
At the correct speed an object will orbit at a constant height and speed.

Question 22

What is red shift?

Answer 22

Light waves are stretched out if a star or galaxy is moving away from an observer. The wavelength of the light increases. This is called red shift because the light is shifted towards the longer wavelength - red end of the visible spectrum

Question 23

What is blue shift?

Answer 23

Light waves are shortened if a star or galaxy is moving towards the observer. The wavelengths would be compressed, making the wavelength shorter. When this occurs, we say the light has been blue shifted

Question 24

What is red shift evidence for?

Answer 24

The faster a star or galaxy is moving away from the observer, the greater the effect of red shift. Red shift is observed in the large majority of galaxies so they are moving away from us and the more distant ones are moving away faster (speed of recession).

Question 25

What did Edwin Hubble suggest (Hint: red shift)

Answer 25

Red shift is evidence for the universe expanding because everything is moving away from everything else

Question 26

What does the big bang theory suggest?

Answer 26

The universe is expanding and originated as a very small and extremely hot and dense region. Red shift provides evidence for this theory because at some point earlier in time, the light must have been extremely short wavelength (high energy) and everything moving apart suggests that everything came from one point.

Question 27

What other evidence is there for the big bang theory?

Answer 27

In 1965, scientists discovered microwaves coming from every direction in space. This microwave radiation had been red shifted, suggesting that 13.5(ish) billion years ago, there must have been a massively energetic event in one place to still have evidence of it today.

Question 28

What does CMBR stand for?

Answer 28

Cosmic Microwave Background Radiation

Question 29

What was the state theory?

Answer 29

The state theory suggested that the universe was expanding, but it had always been there and matter was created into the spaces that the universe expanded into. The state theory is no longer used as new data and evidence has been discovered.

Question 30

What will happen to our universe?

Answer 30

Depending on the total mass of matter int he universe (unknown because we still have not observed dark matter, a strange substance that is needed for galaxies to maintain their shape) the universe could:
1. [If the universe is less dense than a certain amount] expand forever, the stars will gradually die out and the universe will cool (big yawn)
2. [If the universe is more dense than a certain amount] stop expanding and collapse (big crunch) - some scientists currently think the universe has gone through cycles of this.