8 Astrophysics Flashcards
ASTROPHYSICS
Units for:
Mass =
distance =
velocity =
acceleration =
Force =
time =
gravitational field strength =
Mass = kilogram (kg)
distance = metre (m)
velocity = metre per second (m/s)
acceleration = metre per second squared (m/s2)
Force = newton (N)
time = second (s)
gravitational field strength = newton/kilogram (N/kg)
define universe
large collection of billions of galaxies
define galaxy
large collection of billions of stars
which galaxy is our solar system in
milky way galaxy
why gravitational field strength, g, varies and know that it is different on other planets and the Moon from that on the Earth
An object’s gravitational field strength depends on its MASS. A massive object, like a star, will have a very large g-field. The Moon has less mass than the Earth, so its gravitational field is much weaker – approx 1/6th of the Earth’s. This means that we could jump higher on the Moon, and objects would fall more slowly, as they experience a weaker gravitational force.
A planet with a large radius will have a ________ gravitational field at its surface, because the surface is _____ away from the centre of the planet.
weaker
further
explain how gravitational force causes the moon to orbit planets
explain how gravitational force causes the planets to orbit the Sun
explain how gravitational force causes artificial satellites to orbit the earth
explain how gravitational force causes comets to orbit the sun
describe orbit of comet
comets = highly elliptical orbits, with the Sun at one focus. When they come in close to the Sun they speed up, due to the larger gravitational force on them. They also develop bright tails that point away from the centre of the Sun. These are caused by tiny ice crystals that melt and break off from the comet and reflect the bright light of the Sun.
describe differences in orbits of planet and moons
moons = circular orbit
planets = slightly squashed circles , ellipses
describe the evolution of stars of similar mass to the Sun through the following stages: nebula, star (main sequence) , red giant, white dwarf
- nebula
Stars form from large clouds of dust and gas particles (nebulae) that are drawn together by gravitational forces over millions of years. As the particles get closer the temperature and pressure becomes so large that nuclear fusion of hydrogen nuclei to helium nuclei occurs. This releases enormous amounts of energy in the form of heat and light.
- star (main sequence)
Fusion produces forces that make the star expand outwards, but gravitational force is always pulling the particles within the star inwards. When these two opposing forces become balanced a star is stable and called a main sequence star. It should stay this way for millions of years, at a constant size and temperature.
- red giant
Eventually hydrogen fusion stops as the star runs out of fuel. Gravitational force is now bigger than the outward fusion force which causes the star to collapse inwards and compress. This causes it to heat up to even higher temperatures so that fusion of helium nuclei begins. The increased power output causes the star to expand greatly. The surface area is so large that it is cooler than before, so its colour changes to red and the star is called a red giant.
- white dwarf
Eventually fusion stops when the star runs out of helium nuclei and the gravitational force causes the star to collapse inwards and compress again. This heats it up so it changes colour to emit white light. The star is squashed so greatly by the gravitational force to become a small and very dense white dwarf. (They are so dense that a teaspoon full would weigh more than a cruise liner). A white dwarf eventually cools down and change colour as it does so, eventually becoming black.
describe the evolution of stars with a mass larger than the Sun
After the stable period, a giant star expands into red supergiant. (It produces all the elements up to iron during nuclear fusion). When it finally runs out of nuclei to fuse it collapses due to the gravitational force, and then explodes – an exploding star is called a supernova.
The explosion throws dust and gas back into space and so another nebula is formed. A dense core remains – called a neutron star, because it is made entirely from neutrons. If its mass is large enough it can compress further to become a black hole. (Their gravity is so strong that not even light can escape!)
