Gravity Flashcards
(15 cards)
Gravitational field strength
The force that a 1kg mass would experience
Geostationary orbits
- time period of orbit is one day
- orbits around the equator and in the same direction as the earths spin
Keplers 1st law
Every orbit is an ellipse with the sun at one focus
Keplers 2nd law
A line joining a planet and the sun sweeps out equal area in equal time steps
Keplers 3rd law
The square of the orbital period is proportional to the cube of the orbital radius
Gravitational potential
Energy per kg
Why is GPE negative
We define 0J at infinity (earths surface). An object on earth will increase in GP energy as work is done against the earths field. Therefore all GPE’s must be negative.
Gravitational field strength
The force exerted per unit mass on a point mass
Circular orbit
- GPE same everywhere
- KE same, same total energy
- KE = 1/2GPE
Elliptical orbit
Near mass: fast, high KE, low GPE
Furthest from mass: slow, low KE, high GPE
Elliptical orbit: energy argument
As the comet falls towards the sun, GPE decreases (becomes more negative). KE therefore increases as its total energy is constant.
Elliptical orbit: force argument
There is a component of F parallel to V. As F is proportional to ma, the object accelerates, due to work done = force x parallel distance. Work is done by the gravitational field on the object.
Limitations of RADAR
dispersion and attenuation can weaken signals
Parsecs
The distance that corresponds to ‘1 second’ of parallax angle
Hubble’s law
Further away a galaxy, the faster it is receding
