8) Astrophysics Flashcards
Units: 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)
The universe
Large collection of billions of galaxies
A galaxy
Large collection of billions of stars
Why does gravitational field strength vary
-the greater the mass of the planet, the greater its gravitational field strength, larger attractive force towards the centre of the planet or moon
Gravitational field strength on earth vs other planets
Earth: approximately 10 N/kg
Moon: less than earth - easier to lift a mass on the surface of the moon than on Earth
Gravitational force
Provides a force that is pulling smaller bodies towards a star or planet
-gravitational force exerted by the larger body on the orbiting object is always attractive
-force always acts towards the centre of the larger body
-causes the body to move and maintain a circular path
Different astronomical orbits - planets, moons, comets, artificial satellites
-planets orbit the Sun
-moons orbit planets
-comets orbit the Sun
-artificial satellites orbit the Earth or any body in the Solar System
Similarities in the way different planets orbit the Sun
-orbits are all slightly elliptical with the Sun at approximately the centre of the orbit
-all orbit in the same plane
-all travel in the same direction around the Sun
Differences in the way different planets orbit the Sun
-different orbital radius
-different speeds
-different orbital periods
Orbits of moons
-Moons orbit planets in a circular path
-Some planets have more than one moon
The closer the moon is to the planet:
-The shorter the time it will take to orbit
-The greater the speed of the orbit
Orbits of comets
Orbits are highly elliptical (very stretched) or hyperbolic
-Not all comets orbit in the same plane/ direction as the planets
-As the comet approaches the sun, its speed increases - in order to maintain a stable orbit or it will be sucked into the object it is orbiting
-As it moves further away from the sun, its speed decreases
Calculating orbital speed
The time taken for an object to complete one orbit
velocity (m/s) = 2π radius (m)/ orbital period (s)
v= (2πr)/T
Classification of stars
-warm objects emit infrared light
-extremely hot objects emit visible light
-colour they emit depends on how hot they are related to their surface
-astronomical objects cool as they expand, heat up as they contract
blue (hottest) –> white –> yellow –> red (coolest)
Life cycle of stars similar mass to the sun
- Nebula
- Protostar
- Main sequence star
- Red giant
- White dwarf
Life cycle of stars similar mass to the sun - nebula
All stars form from a giant cloud of hydrogen gas and dust called a nebula
Life cycle of stars similar mass to the sun - protostar
The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas - Protostar
-density increases
-more frequent collisions
-temperature increases
Life cycle of stars similar mass to the sun - main sequence star
-Protostar becomes hot enough, nuclear fusion occurs within its core- hydrogen to helium
-thermal expansion due to fusion occur
-force of gravity keeps star in equilibrium
-inward force of gravity = outward pressure force from the expanding hot gases
Life cycle of stars similar mass to the sun - red giant
-After several billion years - hydrogen causing the fusion reactions start to run out
-core shrinks and heats up as the inward force due to gravity > outward force as pressure decreases
-A new series of reactions occur (helium to beryllium)
-As the core shrinks, reactions cause outer part to expand
-Becomes a red giant -red as the outer surface starts to cool
Life cycle of stars similar mass to the sun - white dwarf
-The star will eventually become unstable
-The core which is left behind will collapse completely, due gravity, becomes white dwarf
-cools, amount of energy emitted decreases
Life cycle of large stars
- Nebula
- Protostar
- Main sequence star
- Red super giant
- Supernova
- neutron star/ black hole
Life cycle of large stars - red super giant
-After several billion years - hydrogen causing the fusion reactions start to run out
-core shrinks and heats up as the inward force due to gravity > outward force as pressure decreases
-A new series of reactions occur (helium to beryllium)
-As the core shrinks, reactions cause outer part to expand, becomes red super giant
Life cycle of larger stars - supernova
-fusion reactions finish
-the core of the star will collapse causing a gigantic explosion - supernova
Life cycle of larger stars - neutron star
-At the centre of this explosion (supernova) a dense body - neutron star - will form
Life cycle of larger stars - black hole
-In the case of the largest stars, the neutron star will continue to collapse under the force of gravity until it forms a black hole
-A black hole is an extremely dense point in space that not even light can escape from
