section 8: Astrophysics

Question 1

important units:

Answer 1

-kilogram (Kg)
-metre (m)
-metre/second (m/s)
-metre/second^2 (m/s^2)
-newton (N)
-second (s)
-newton/kilogram (N/kg)

Question 2

important terms: universe, galaxy and solar system

Answer 2

-the universe: is a large collection of billions of galaxies
-a galaxy: is a large collection of billions of stars
-a solar system: is a collection of plantes orbiting a common star, our solar system is in the Milky Way galaxy

Question 3

gravitational field strength:

Answer 3

-the gravitational field strength is the force per unit mass on a body in a gravitational field and is measure in Newtons per kilogram (N/kg)
-it varies with the mass and size of the body and is therefore different on other planets and the moon compared to the earth
weight = mass x gravitational field strength
W = mg

Question 4

gravitational force:

Answer 4

-gravitational forces enables the various bodies to orbit around other, for example:
-moons orbit plants -> the orbits are slightly elliptical with near constant orbital speed
-planets and comets orbit the sun -> the orbits of planets are slightly elliptical with near constant orbital speed, the orbits of comets are highly elliptical
-artificial satellites orbit the earth

Question 5

formula linking orbital speed, orbital radius and time period:

Answer 5

-the greater the orbital radius or the smaller the time period, the greater the orbital speed:
orbital speed = 2 x pi x orbital radius/time period
v = 2πr/T
-comets have a greater speed nearer to the star (when r is smaller) because the ice inside them melts as they get closer (and warmer)-causing their mass to decrease

Question 6

stellar evolution:

Answer 6

-a star begins as a cloud of dust and gas called a nebula, the particles experience a weak attraction towards each other due to gravity and begin to clump together
-they continue to clump together until the pressure and temperature is great enough for nuclear fusion to occur
-hydrogen nuclei fuse together to form helium nuclei which releases a large amount of energy and causes a great outwards pressure
-this outwards pressure balances with the inwards pressure due to gravity and the star is now stable and called a main sequence star
-eventually the hydrogen star is used up, there is no longer enough outwards pressure from nuclear fusion and it collapses under its own gravitational attraction, becoming unstable
-if the star has a similar mass to the sun, it expands massively and becomes a red giant, it then becomes a white dwarf (and finally cools into a black dwarf)
-if the star has a mass larger than the sun, it exapnds and becomes a red super giant, before exploding into a supernova, what remains is either a neutron star, or if it was expecionally massive, a black hole

Question 7

classification of stars:

Answer 7

-stars can be classified according to their colour, the colour of a star is related to its surface temperature, with hotter stars being bluer and cooler stars being redder