astro

how to find particle denisty

number of particles / volume

density / mass of particle

how to find number of particles

mass of universe/mass of particle

what is the composition of the universe

90% H, 10%He, 0.01% everything else

how to find number of molecular gas

density / (2 x mass of hydrogen)

how to find number of atomic gas

density / mass of hydrogen

how to find number of ionized gas

( 2 x density) / mass of hydrogen

what is the force of gravity

weak, attractive, radial force

what is the total energy of an object

start energy + energy gained ( not linked to speed )

what is the work done due to energy

derived from integrating the gravitational force, as F is not constant with r

what is the escape velocity of an object

KE = gravitational

what is the orbital velocity of an object

gravitational = centripetal

what is kepler’s first law

planets orbit in ellipses with sun at one focus not the centre

how to find eccentricity of an orbit

sqrt ( 1 - (b/a)² )

what is kepler’s second law

planets sweep out equal areas in equal times, as there is a conservation of angular momentum (m v r sintheta)

what is kepler’s third law

period² = r³

what is a binary system

centre of mass is stationary and shared, objects are on opposite sides to conserve momentum and have the same period