Rotational Motion and Astrophysics Flashcards
Define gravitational potential.
The work done by an external force in moving a unit mass from infinity to a point in a gravitational field.
Define the conservation of angular momentum
Angular momentum is conserved in the absence of external torques.
Total angular momentum before = total angular momentum after, in the absence of external torques.
Define Gravitational field strength
The gravitational force acting on a unit mass.
g=F/M
Define ‘Escape velocity’
Escape velocity is the minimum velocity required to just escape a planet’s gravitational field and reach infinity with zero kinetic energy or zero velocity.
Will a high moment of inertia mean an object spins faster or slower?
High moment of inetria= spins slower
(Rotating bodies veritasium video)
What is Centripetal Force?
It is the unbalanced force which keeps an object moving in a circle.
Define Schwarzschild Radius
The distance from the centre of the black hole to it’s event horizon.
State what it is meant by the ‘Equivalence Principle’
It is impossible to tell the difference between the effects of a uniform gravitational field and of a constant acceleration.
What is it meant by an inertial frame of reference?
An inertial frame of reference is one that is non-accelerating/ has a constant velocity. (Theory of Special Relativity)
What is it meant by a non-inertial frame of reference?
A non-inertial frame of reference is one that is accelerating. (Theory of General Relativity)
World Lines
Will clocks run slower or faster in a stronger gravitational field?
Clocks run slower in a stronger gravitational field (compared to clocks in a weaker gravitational field).
What is the value of the Universal constant of gravitation? (G)
G = 6.67x10-11 m3 kg-1 s-2
Define Velocity
Velocity is the rate of change of displacement with time.
Define Acceleration
Acceleration is the rate of change of velocity with time.
How are displacement, velocity and acceleration linked?
a= dv/dt
v= ds/dt
s
What tool can you use to find the area under a line on a graph?
Integration.
What is the area under the velocity-time graph equal to?
Displacement
What is it meant by the ‘moment of inertia of an object’?
It is a measure of the object’s reluctance to a change in its rotational motion.
What is moment of inertia dependant upon?
The mass and the distribution of mass about a given axis of rotation.
Does the path taken to move a mass between two points in a gravitational field affect the energy required to move that mass?
No.
The energy required to move a mass between two points in a gravitational field is independent of the path taken.
What is spacetime considered to consist of?
3 dimensions of space and 1 dimension of time.
What is a geodesic?
A path with the shortest distance between two points.
What is the escape velocity from the event horizon of a black hole equal to?
The speed of light.
If you looked at the event horizon of a black hole, what would you describe time to appear as?
Time would appear to be frozen to a distant observer at a black hole’s event horizon.
How are stars born?
Stars are formed in interstellar clouds.
Gravitational forces overcome thermal pressure and cause a molecular cloud to contract until the core becomes hot enough to sustain nuclear fusion.
This provides a thermal pressure that balances the gravitational force.
What does the mass of a star determine?
Its lifetime.
What does light or a freely moving object follow in spacetime?
A geodesic
What is meant by a ‘black body’?
A black body absorbs radiation and emits radiation at the same rate.
What is one assumption we make about stars?
That all stars behave as black bodies
A black body absorbs radiation and emits radiation at the same rate
CFE Specimen Q4, https://lco.global/spacebook/light/black-body-radiation/#:~:text=Stars%20behave%20approximately%20like%20blackbodies,green%20part%20of%20the%20spectrum.
