Rotational Motion & Astro

Question 1

Centripetal acceleration

Answer 1

Constant speed.
Direction is changing.
Velocity is vector (magnitude and direction). ^ velocity is changing.
If velocity changes object is accelerating

Question 2

Moment of inertia

Answer 2

Measure of resistance to angular acceleration about a given axis.

Question 3

Torque

Answer 3

Turning effect of a force

Question 4

Angular momentum

Answer 4

Total angular momentum is conserved when two or more objects are collided in the absence of external torques

Question 5

Gravitational field strength

Answer 5

Gravitational force per kilogram

Question 6

Satellite motion

Answer 6

Satellites are kept in orbit around a planet by the gravitational force which provides the centripetal force

Question 7

Gravitational potential

Answer 7

Work done in moving a unit mass from infinity to that point

Infinity is where the gravitational force is 0N

Question 8

Escape velocity

Answer 8

Minimum velocity required to allow a mass to escape GRAVITATIONAL FIELD to infinity with zero kinetic energy and zero potential energy

Question 9

Equivalence principle (general relativity)

Answer 9

It is not possible to distinguish between the effects on an observer in a uniform gravitational field or at a constant acceleration

Question 10

Space time

Answer 10

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

Question 11

Gravitational lending (bending of light)

Answer 11

A large mass (high gravitational field) can make light bend.

Light still travels in a straight line but space time is curved.

Question 12

Geodesic

Answer 12

Light/objects follow the shortest distance between two points in space time knows as geodesic

Question 13

Gravitational time dilation

Answer 13

Time will run slower (dilate) under the influence of greater gravity

Time will change with altitude above a planet surface
“The lower the slower”

Question 14

Black whole creation

Answer 14

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

Question 15

Schwartzchild radius

Answer 15

The distance from a centre of mass where the escape velocity is equal to the speed of light

Question 16

Luminosity of star

Answer 16

Total energy radiated per second (or power radiated)

Question 17

Apparent brightness

Answer 17

Amount of energy per second (power) detected per unit area (metre square)

Question 18

Assumptions made about stars

Answer 18

Perfectly spherical

Uniform surface temperature

Perfect black bodies (I.e. absorb/emit all wavelengths of radiation)

Question 19

Star formation

Answer 19

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

Question 20

Red giant branch

Answer 20

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