Rotational Motion And Astrophysics Flashcards
What is the angular velocity of a rotating object defined as?
The rate of change of angular displacement or the change in angular displacement per unit time
What is angular acceleration defined as?
The rate of change of angular velocity
Wgat is tangential acceleration defined as?
The rate of change of tangential or linear velocity
What is centripital acceleration defined as?
The rate of change in linear velocity
What direction is centripital acceleration always towards?
The centre of the cirlce
What is centripital acceleration always at a right angle to?
The tangential acceleration
What is torque defined as?
The product of radius and force applied at that radius to an axis of rotation.
What is the moment of inertia of a mass defined as?
A measure of its resistance to angular acceleration about a given axis.
When is angular momentum conserved?
When two or more objects collide in the absence of external torques
What happens when torque does work on a body to make it rotate?
It gains kinetic energy
What is gravitational field strength defined as?
The force per unit mass at a point.
How are satellites held in orbit around the Earth?
It is as a consequence of the Earth’s gravitational force which provides a centripetal force on the satellite.
What is gravitational potential at a point in space defined as?
The work done by external forces to move unit mass from infinity to that point
What is the value of both gravitational potential and gravitational potential energy at infinity?
Zero
What is gravitational potential proportional to?
1/r
What is gravitational force proportional to?
1/r^2
What is step 3 of the proton-proton chain?
Two helium-3 nuclei fuse to form helium-4
Two protons are released at the same time
What is step 2 of the proton-proton chain?
The deuterium nucleus fuses with a proton to produce helium-3
A gamma ray is released as the same time
This happens twice
What is step 1 of the proton-proton chain?
Two hydrogen nuclei (protons) combine to form a deuterium nucleus
A positron and a neutrino are released at the same time
This happens twice
What are the axis on the Hertzsprung-Russel diagram?
x = Surface temperature (K) y = Luminosity
What are the groups called in the Hertzsung-Russel diagram?
Main sequences
Giants
Supergiants
White dwarfs
What is the formula for the apparent brightness of a star?
b = L/4πr^2 b = Apparent brightness L = Luminosity r = Distance from Earth
What is the equation for the luminosity of a star?
L = 4πr^2σT^4 L = Luminosity r = Radius T = Surface temperature
What is the definition for luminosity?
The total energy radiated per second by the star
What is the definition for apparent brightness of a star?
The amount of energy per second from the star landing normally on 1 square metre at the surface of the Earth
Why do high mass stars have shorter lifetimes than low mass stars?
They start with a greater supply of fuel but they use it up at a greater rate
Where are stars formed?
Inside relatively dense clouds of gas and dust
What is escape velocity defined as?
The minimum velocity required to allow a mass to escape a gravitational field, achieving zero kinetic energy and maximum (zero) gravitational potential energy at infinity
What does the equivalence principle state?
No observer can determine by experiment whether they are in an accelerating frame of reference or in a gravtational field. The laws of physocs cannot be distinguished between acceleration and gravity
When will time run slower?
Under the influence of greater gravity
What is the event horizon?
The boundary between the inside of a black hole and the outside universe
What is the escape velocity from from the event horizon of a black hole?
Equal to the speed of light
The event horizon of a black hole forms a sphere. What is the radius of this sphere called?
The Schwarzschild radius
What is the luminosity of a star?
The total energy radiated per second by the star
What is the apparent brightness of a star?
The amount of energy per second from the star landing normally on 1 square metre at the surface of the Earth
What produces an angular acceleration?
An unbalanced torque
What is the unit of torque?
Nm
What does the angular acceleration produced by an unbalanced torque depend on?
The moment of inertia of the object
What does the moment of inertia of an object depend on?
The mass of the object, and the distribution of the mass about a particular axis
What is the angular momentum of a rigid object the product of?
Moment of inertia and angular velocity.
In the absence of external torques, what is the total angular momentum of a rotating rigid object before a collision equal to?
The total angular moment after impact
What does the rotational kinetic energy of a rigid object depend on?
Its moment of inertia and angular velocity.
What value does gravitational potential and gravitational potential energy have at infinity
Zero
What does Special Relativity deal with?
Motion in inertial (nonaccelerating) frames of reference.
What does General Relativity deal with?
Motion in non-inertial (accelerating) frames of reference
What is the Equivalence Principle?
An observer cannot tell the difference between a uniform gravitational field and a constant acceleration
Describe the consequences of the Equivalence Principle
Clocks in non-inertial reference frames e.g. accelerating spacecraft
Clocks at altitude i.e. clocks run at different speeds in different gravitational field strengths
Precession of Mercury’s orbit
Gravitational lensing of light
What is spacetime a representation of?
Four dimensional space
What path does light or a freely moving object follow in spacetime?
A geodesic (the shortest distance between two points)
What does mass do to spacetime?
Curves it
How does gravity arise?
From the curvature of spacetime
What happens to time at the event horizon of a black hole?
It appears to be frozen
