Rotational Motion & Astro Flashcards
Centripetal acceleration
Constant speed.
Direction is changing.
Velocity is vector (magnitude and direction). ^ velocity is changing.
If velocity changes object is accelerating
Moment of inertia
Measure of resistance to angular acceleration about a given axis.
Torque
Turning effect of a force
Angular momentum
Total angular momentum is conserved when two or more objects are collided in the absence of external torques
Gravitational field strength
Gravitational force per kilogram
Satellite motion
Satellites are kept in orbit around a planet by the gravitational force which provides the centripetal force
Gravitational potential
Work done in moving a unit mass from infinity to that point
Infinity is where the gravitational force is 0N
Escape velocity
Minimum velocity required to allow a mass to escape GRAVITATIONAL FIELD to infinity with zero kinetic energy and zero potential energy
Equivalence principle (general relativity)
It is not possible to distinguish between the effects on an observer in a uniform gravitational field or at a constant acceleration
Space time
The three dimensions of space (x,y,z) and time (t) are unified through space time.
Mass curves space time, gravity is due to the curvature of space
Gravitational lending (bending of light)
A large mass (high gravitational field) can make light bend.
Light still travels in a straight line but space time is curved.
Geodesic
Light/objects follow the shortest distance between two points in space time knows as geodesic
Gravitational time dilation
Time will run slower (dilate) under the influence of greater gravity
Time will change with altitude above a planet surface
“The lower the slower”
Black whole creation
Star runs out of file for fusion
Gravitational compression will cause it to collapse to a very small radius (same mass)
This very dense body is called a black hole
Very dense = very strong gravitational field/ severely curved space time
Schwartzchild radius
The distance from a centre of mass where the escape velocity is equal to the speed of light
Luminosity of star
Total energy radiated per second (or power radiated)
Apparent brightness
Amount of energy per second (power) detected per unit area (metre square)
Assumptions made about stars
Perfectly spherical
Uniform surface temperature
Perfect black bodies (I.e. absorb/emit all wavelengths of radiation)
Star formation
Stars are formed in interstellar clouds (nebulae).
Gravitational forces cause particles to be pulled into a central core.
When the core is hot enough to sustain nuclear fusion the outwards thermal pressure is balanced by inwards gravitational forces
Red giant branch
Hydrogen fusion in core supplies energy to maintain the outward thermal pressure that balance onwards gravitational forces
When hydrogen is depleted nuclear fusion in core stops
Hydrogen in shell surrounding core continues fusing,adding more helium to core
Gravitational forces causes core to contract ^heating core up
Outward thermal pressure increase ^volume (radius) of star increase
