sem 2 ao1; moments, momentum and astrophysics
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96 Terms
Term
Definition
Units (kg)
Unit of mass
Units (m)
Unit of distance/displacement
Units (m/s)
Unit of speed/velocity
Units (m/s²)
Unit of acceleration
Units (N)
Unit of force/weight
Units (s)
Unit of time
Units (N/kg)
Unit of gravitational field strength (g)
Universe
A vast collection of billions of galaxies.
Galaxy
A large collection of billions of stars
Our Solar System
Located in the Milky Way galaxy.
Gravitational Field Strength (g)
The force per unit mass experienced in a gravitational field (N/kg). Varies depending on mass and radius of celestial body. Earth approx. 9.8 N/kg.
Gravitational Force
An attractive force between any two objects with mass. Causes orbits of moons
Planet Orbits
Generally elliptical (close to circular) around the Sun. Speed depends on distance (closer = faster).
Moon Orbits
Generally elliptical around planets. Speed depends on distance.
Comet Orbits
Highly elliptical around the Sun. Speed varies greatly (fastest near Sun).
Orbital Speed (v)
The speed at which an object orbits a central body.
Orbital Radius (r)
The average distance between the orbiting object and the center of the central body.
Time Period (T)
The time taken for one complete orbit.
Orbital Speed Formula
v = (2πr) / T
Star Classification by Colour
Stars classified by their colour
Star Colour and Temperature
Hotter stars: blue/white. Cooler stars: red/orange. Medium stars (like Sun): yellow.
Nebula
A large cloud of gas and dust; the birthplace of stars.
Main Sequence Star
Stable phase of a star's life where hydrogen fuses into helium in the core.
Red Giant
Star expands and cools after hydrogen fuel runs out in the core.
White Dwarf
Hot
Supernova
Massive explosion of a star with a large mass after its iron core collapses.
Neutron Star
Extremely dense object made of neutrons
Black Hole
Region of spacetime with gravity so strong nothing can escape
Brightness (Apparent Magnitude)
How bright a star appears from Earth
Absolute Magnitude
The brightness a star would have at a standard distance of 10 parsecs
Hertzsprung-Russell (HR) Diagram
Graph plotting luminosity (or absolute magnitude) of stars against their temperature (or colour).
HR Diagram - Main Sequence
Diagonal band on HR diagram where most stars (including Sun) lie
HR Diagram - Red Giants/Supergiants
Upper right of HR diagram
HR Diagram - White Dwarfs
Lower left of HR diagram
Investigating Extension with Force (Practical)
Measure extension of spring/wire/band with varying forces
Hooke's Law
Extension of an elastic material is directly proportional to the force applied (F=kx)
Elastic Behaviour
Ability of a material to return to its original shape after deforming forces are removed.
Elastic Limit
Maximum force/stress before permanent deformation (plastic deformation) occurs.
Momentum (p)
A measure of the motion of an object (p = mv). Vector quantity.
Momentum Formula
p = m × v
Safety Features and Momentum
Increase the time taken for momentum to change during collisions to reduce force (e.g.
Conservation of Momentum
In a closed system
Force and Change in Momentum
Force is equal to the rate of change of momentum (F = Δp / Δt).
Newton's Third Law
For every action
Moment of a Force (Torque)
The turning effect of a force about a pivot (M = F × d).
Moment Formula
moment = force × perpendicular distance from the pivot
Centre of Gravity
The point at which the entire weight of an object appears to act.
Principle of Moments (Equilibrium)
For an object in rotational equilibrium
Forces on a Light Beam with Heavy Object
Upward support forces vary with the heavy object's position to maintain equilibrium (closer object = larger force on that support).
Note 
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