4.8- Space Physics

What is a solar system

A collection of stars, planets, dwarf plants, asteroids, comets and satellites in orbit

What is a satellite

An object which orbits a planet- can be natural or artificial

What is an asteroid

Rock orbiting the sun

What is a comet

Icy rock orbiting the sun

What is a galaxy

A collection of stars and planets

Describe the formation of a main sequence star

• Cloud of gas (mostly hydrogen) and dust called a nebula is disturbed, causing the particles to be pulled together by gravitational forces

• As the particles get closer together, they form a hot rotating ball called a protostar

• As the protostar becomes more dense, particles collide more and get hotter, as GPE is converted into thermal energy

• If the protostar becomes hot enough, fusion may occur between hydrogen nuclei to form helium nuclei- this is a main sequence star. In a main sequence star, the inward gravitational forces are in equilibrium to the outward radiation pressure forces causes by nuclear fusion

Describe the second part of the life cycle of stars with a similar or lower mass than our sun

• As the hydrogen runs out, the core collapses, and the outer layers expand to form a red giant

• Since the core is now much denser and therefore hotter, helium nuclei now fuse to form heavier elements- nuclear fusion of elements as heavy as iron are formed here

• When there are no more light elements left in the core, the core collapses in on itself as there is no outward pressure from fusion- the collapsed core forms a white dwarf, a hot iron sphere - it continues to glow from left over energy from fusion

• Finally, as it runs out of energy, it cools down to form a black dwarf

Describe the second part of the life cycle of stars with a much greater mass than our sun

• As the hydrogen runs out, the core collapses, and the outer layers expand more dramatically to form a red super giant, similar to a red giant

• The red super giant then rapidly collapses, and forms a huge explosion called a supernova- in this all elements heavier than iron are formed

• If the mass is great enough, the collapsed core will form a black hole, which has a gravitational field so strong nothing can escape it, not even light; if not it will form a neutron star, an incredibly dense star in which protons absorb electrons to form neutrons

How do circular orbits work

• The forces of gravity pull the planet toward the centre of the sun and cause it to accelerate towards it

• The force of the planet moving is perpendicular to the forces of gravity from the sun

• As a result a circular orbit is produced

• The magnitude of the velocity of the planet in circular orbit doesn't change, as it maintains the same speed (if the radius of the orbit is constant, so is the speed) but the direction of the velocity constantly changes, as the orbital path is circular

Explain why the velocity of a satellite changes as it orbits the Earth.

• Force of gravity causes the satellite to accelerate towards the Earth

• The acceleration causes a change in direction

• Velocity changes because direction changes

For a stable orbit, what will happen to the radius of the orbit (the distance from the sun) if the planet speeds up

The radius must decrease as more gravitational forces are required to keep the planet in orbit, so it must move closer to the sun

Order these objects from lowest to highest orbit- geostationary satellite, GPS satellite which goes around the earth once every 12 hours, weather satellite which goes around the earth once every 3 hours

weather, GPS, geostationary (this completes one all orbit once every 24 hours, so moves at the same speed the earth spins, so keeps the same position above the earth)

The lower the satellite, the faster the orbit

How can red shift provide evidence of an expanding universe

There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. This effect is called red-shift.

The observed red-shift provides evidence that space itself (the universe) is expanding and supports the Big Bang theory.

What does the big band theory suggest

The Big Bang theory suggests that the universe began from a very small region that was extremely hot and dense.

What is seen the further a universe is from earth

• The further away the galaxy, the more it is red shifted

• This means the further away a galaxy, the faster it is moving away from us

• This means that the galaxies is accelerating, from one small area away from each other

• This shows the universe is expanding and supports the Big Bang theory

What is still unknown about the universe

• Dark matter- there is unaccounted for mass in the universe which doesn’t interact with light- it means that the averse density of the universe is much larger than expected

• Dark energy- scientists have proven, based on the observations of supernovae, that the universe is expanding exponentially, yet the only force which could cause this is gravity, which would do the opposite. So there must be some unknown force, driving the acceleration, and this is believed to be dark energy