Rotational Motion & Astrophysics Flashcards
Definitions from AH unit 1
What is a Circumference?
The Length of the Perimeter of a Circle
What is an Arc?
The length of a section of the Circumference of a Circle
What is a Diameter?
The Length of the Line connecting opposite sides of a Circle through its center
What is a Radius?
The Length of the Line connecting the Edge of a Circle to its center
What is a Tangent?
A Line at a right angle to the Radius that ‘touches’ the edge of a Circle.
How many radians for 1 complete circle?
2π radians
What is meant by “Angular displacement”?
The change in angular position between two points.
What is meant by “Angular Velocity”?
The rate of change of Angular Displacement
What is meant by “Periodic time”?
Time taken for 1 complete revolution
What is meant by “Angular acceleration”?
The rate of change of Angular Velocity
How to convert between Revolutions and radians
Multiply number of revolutions by 2π
What is meant by “Radial acceleration”?
Acceleration towards the centre of a circular path.
What is meant by “Centripetal force”?
Any force that acts radially towards the center of a circular path.
What is meant by “Torque”?
The moment (angular equivalent) of a force.
What is meant by “Angular Momentum”?
The moment (angular equivalent) of linear momentum.
What is the “Law of conservation of angular momentum”?
The Total Angular Momentum before a collision will equal the Total Angular Momentum after a collision, as long as no external Torques act upon the system.
What is meant by “Gravitational Force”
The Force between two objects with mass. It is proportional to magnitude of the masses, and inversely proportional to the square of the radius between them.
What is meant by “Gravitational field strength”?
The force experienced by a unit mass (1kg) at that point in a gravitational field.
What is meant by “Gravitational Potential”?
The work done by an external force to move a unit mass from infinity to that point.
What is meant by a “Conservative field”?
The energy required to move between two points is independent of the path taken.
What is meant by a “Potential well”?
The 3d representation of the changing gravitational potential around a mass.
What is meant by “Escape velocity”?
The initial velocity at which an object would have suffient energy to move from its starting radius to infinity.
What is meant by the “Schwarzschild radius”?
The radius from the center of an object at which its escape velocity is equal to the speed of light.
What is meant by a “Black body object”
An object that is perfect absorber and emitter of radiation.
Which type of Fusion occurs within stars on the “Main sequence” of an H-R diagram?
Proton-Proton Chain fusion
Which type of Fusion occurs within stars on the “Giant branch” of an H-R diagram?
Fusion of helium and heavier elements
Which type of Fusion occurs within stars on the “Dwarf” section of an H-R diagram?
No fusion takes place.
What is the end of life point for a low mass star?
(White) dwarf
What is the end of life point for a medium mass star?
Neutron star
What is the end of life point for a high mass star?
Black hole
Which two forces determine the radius of a star?
Gravitational force & Thermal pressure
What is meant by a “Non inertial” frames of reference?
Reference frames which are accelerating relative to each other.
What is the “Equivalence principle”?
No experiment can differentiate between the effect of a Uniform Gravitational field and an accelerating reference frame.
What is meant by a “Geodesic”?
The shortest posssible route through curved Space-Time.
Why does “Gravitational redshift” occur?
As the Photon moves away from the Mass, Work must be done to escape the Gravity Well. This causes the Photon’s energy to reduce, reducing the frequency.
What is meant by “Space-Time”?
A 4-dimensional coordinate system which takes into account that an event will occur at a location with a set 3-dimensional position (x,y,z ) and time (t).
