Space Physics

Question 1

Why do planets orbit the sun?

Answer 1

The sun contains most of the mass in the solar system so it has the strongest gravitational field strength

Question 2

Why are the inner planets rocky and the others gassy.

Answer 2

The heat and radiation from the sun forced the lighter elements(gases) further away.
So the closer planets were formed of heavier and rocky elements. The farther planets were formed mostly of gas.

Question 3

What is gravitational field strength?

Answer 3

Force per unit mass acting on an object in the field.

Question 4

How does nuclear fusion begin in a star?

Answer 4

• after the formation of a protostar, gravity pulls in mass and gasses. Bringing them closer and heating them up.
• the gasses become hot and compressed, reaching the temperature and pressure high enough to trigger NUCLEAR FUSION.

Question 5

How was our solar system formed? [5]

Answer 5

• began as a swirling ball of dust and gas(hydrogen) called a nebula
• gravity pulls mass to the centre, collapsing the nebula inwards forming a protostar.
• this becomes a stable star when the inward force of the gravity is equal to the outward force of the heat from the star.
  (The inward force = outward force0
• the remaining gas and dust(mass) which was not pulled to the centre form a rotating accretion disc.
• these masses are then slowed by collision and pulled into clumps by gravity to make larger rocks that orbit the sun called proto planets which are then formed into planets.

Question 6

What is accretion?

Answer 6

Gradual growth by the addition of material.

Question 7

What does gravitational field strength depend on?

Answer 7

1. The mass. Greater mass, greater field strength on the surface of the planet.
2. Distance. The larger the distance from the planet the weaker the field strength.

Question 8

What keeps an object in orbit around the sun?

Answer 8

The gravitational attraction of the sun.

Question 9

Why do the outer planets have a longer orbital period?

Answer 9

The strength of the sun’s gravitational field decreases with distance.
The further a planet is from the sun, the weaker the gravitational pull(force) of the sun and the slower it’s speed.

Question 10

Why do objects in elliptical orbits travel faster when closer to the sun?

Answer 10

The farther away an object is from the sun, the more gravitational potential energy it will gain and loose kinetic energy.
When close to the sun, it looses it’s gravitational potential energy and gains kinetic energy.

Question 11

Does gravitational POTENTIAL energy increase with distance?

Answer 11

Yes.

Question 12

Does gravitational FIELD force increase with distance?

Answer 12

No.

Question 13

Which of these have elliptical orbits?
A. The minor planets
B. The major planets
C. Comets

Answer 13

A and C

Question 14

How does orbital distance affect gravitational attraction from the sun?

Answer 14

The larger the distance the weaker the gravitational attraction to the sun.

Question 15

What does the density of a planet imply?

Answer 15

The lower the density the larger the size of the planet.
(Gas giants have low density and large volume

Question 16

What else can affect the surface temperature of a planet?

Answer 16

• the color, black or white. Absorber and emitter.
• if the planet has an atmosphere. A planet without an atmosphere cannot retain heat so it heats up quickly and looses heat quickly.

Question 17

Mention 4 properties of the sun

Answer 17

• it is of medium size
• contains mostly hydrogen and helium
• it radiates most of its energy in infrared, visible and ultraviolet regions of the electromagnetic spectrum.
• it is powered by nuclear fusion

Question 18

How are stars powered? And how is it different for stable stars?

Answer 18

By nuclear reactions (fusion) that release energy.
In stable stars, the nuclear reactions involve the fusion of hydrogen into helium.

Question 19

What is the closest star to Earth?

Answer 19

The sun.

Question 20

When is a star stable?

Answer 20

When the inward force of gravity is equal to the outward force of the heat from the fusion reaction.

Question 21

What is the value of a light year?

Answer 21

9.5*10^15m
(The speed of light

Question 22

What is the definition of a light year?

Answer 22

The distance travelled by light in (the vacuum of) space in one year.

Question 23

Explain the life cycle of a star [8]

Answer 23

1. A star is formed from interstellar clouds of gas and dust that contain hydrogen - nebula.
2. A protostar is an interstellar cloud collapsing and increasing in temperature as a result of its internal gravitational attraction
3. A protostar becomes a stable star when the inward force of gravitational attraction is balanced by an outward force due to the high
   temperature in the centre of the star
4. All stars eventually run out of hydrogen as fuel for the nuclear reaction
5. Most stars (medium stars) expand to form red giants and more massive stars expand to form red supergiants when most of the hydrogen in the centre of the star has been converted to helium
6. Red giants shed their outer layers leaving behind a hot and dense core called a white dwarf. (Still considered as a star). This uses helium as its nuclear fusion converting it to carbon. When fusion stops the star cools and fades forever.
7. A red supergiant explodes as a supernova, forming a nebula containing hydrogen and
   new heavier elements, leaving behind a neutron star or a black hole at its centre
8. The nebula from a supernova may form new stars with orbiting planets

Question 24

State two properties of our Milky Way galaxy.

Answer 24

• There are 100 billions of stars in a galaxy.
• the diameter of the milky way is approximately 100 000 light years.

Question 25

What do supernova’s form when they explode?

Answer 25

Interstellar nebulas

Question 27

What do red giants form?

Answer 27

Planetary nebula with a white dwarf at the centre.

Question 28

Difference between interstellar nebula’s and planetary nebular’s.

Answer 28

Interstellar nebula’s are formed from supernova’s. It is formed away from it’s previous solar system.
Planetary nebular is from a medium sized star.

Question 29

What does red shift prove?

Answer 29

It is evidence that the distance between distant galaxies is increasing, thus the universe is expanding.

Question 29

What is redshift?

Answer 29

an increase in the observed
wavelength of electromagnetic radiation emitted from receding stars and galaxies

Question 30

How does the red shift support the big bang theory?

Answer 30

As the galaxies appear to be moving apart, they may have once been together in the same space.

Question 31

What is CMBR?

Answer 31

Cosmic Microwave Background Radiation.

Question 32

Define CMBR.

Answer 32

Microwave radiation of a specific frequency is observed at all points in space around us.

Question 33

What is the Doppler Effect?

Answer 33

The increase in the wavelength of light waves (electromagnetic radiation) from objects moving away from earth at high speeds.

Question 34

When was CMBR formed?

Answer 34

After the universe was formed. The radiation has been expanded into microwave region of the electromagnetic spectrum as the universe expanded

Question 35

What is Hubble’s constant?

Answer 35

The ratio of the speed v at which the galaxy is moving away from the earth to its distance from the earth.
v/d

Question 36

What is the value and unit of the Hubble’s constant.

Answer 36

2.2 * 10^-18 per second.

Question 37

How do we calculate the speed at which a galaxy is moving away from Earth (receeding).

Answer 37

can be found from the change in wavelength of the galaxy’s starlight
due to redshift

Question 38

How do we calculate the distance of a far galaxy?

Answer 38

using the brightness of a supernova in the galaxy

Question 39

What does this represent and prove?
D/v = 1/Ho

Answer 39

an estimate for the age of the Universe and this is evidence for the idea that all the matter in the Universe was present at
a single point