Physics Definitions Unit 3

Angular Velocity ⍵ (circular motion)

Rate of change of angle with time

Radian (circular motion)

angle when arc length is equal to radius

Why does and object moving at a constant speed in a circle have acceleration? (circular motion)

velocity is a vector - direction changes but not magnitude

acceleration = rate of change of velocity

Where is greatest tension in a vertical circle? (circular motion)

the bottom

Where is least tension in a vertical circle? (circular motion)

the top

Simple Harmonic Motion (SHM)

The acceleration of the body is directly proportional to its distance from a fixed point and is always directed towards that point 

Period (SHM)

The time for one complete oscillation or cycle

Frequency (SHM)

number of cycles completed per second

amplitude (SHM)

maximum displacement from equilibrium position

Phase constant ε (SHM)

angular displacement when displacement (x) = 0

Damping (SHM)

the process whereby energy is taken from an oscillating system and the oscillations decrease as a result

Types of damping (3) (SHM)

Light, Heavy, Critical

Time taken for system to return to equilibrium in critical damping? (SHM)

usually ¼ T

Free Oscillations (SHM)

Oscillating body has no force applied and vibrates at its natural frequency 

(displacement applied then released)

Forced oscillations (SHM)

System vibrating due to periodic application of external driving force

Resonance (SHM)

driving force of a oscillating system with a frequency that matches the natural frequency, resulting in a large amplitude

Ideal gas assumptions (kinetic theory) (4)

1. collisions of gas molecules are perfectly elastic

2. intermolecular forces are negligible, except during collision

3. gas molecules move rapidly and randomly

4. volume of molecules is negligible compared to volume of gas

Avogadros constant (kinetic theory)

number of particles per mole

Radioactive Atom (radioactivity)

atom with an unstable nucleus

alpha particle (radioactivity)

2 protons and 2 neutrons

helium nucleus

beta particle (radioactivity)

electron

how fast are is beta radiation? (radioactivity)

just less than the speed of light

gamma radiation (radioactivity)

high energy, high frequency electromagnetic wave

Half-life (radioactivity)

time taken for the number of radioactive nuclei to half

3 methods of distinguishing between alpha, beta and gamma radiation? (radioactivity)

differing penetration, deflection by electric field, deflection by magnetic field

results for differing penetration (radioactivity)

alpha - decrease with paper absorber

beta - further decrease with 3mm aluminium

gamma - further decrease with 3cm lead

results for deflection by electric field (radioactivity)

alpha - attracted by negative plate 

beta - attracted by positive plate

gamma - no change 

results for deflection by magnetic field (radioactivity)

alpha - deflected

beta - deflected more in opposite direction

gamma - no change

ion (radioactivity)

an atom which has lost of gained one or more electrons

Activity (radioactivity)

number of radioactive disintegrations per second

rate of decay

Becquerel (Bq) (radioactivity)

one disintegration per second

what does the decay constant determine? (λ) (radioactivity)

rate of decay

Internal energy (thermal physics)

sum of the random KE and PE of the molecules

potential energy of gases (thermal physics)

0 because negligible intermolecular forces

Absolute zero (thermal physics)

the temperature when internal energy is a minimum

heat (thermal physics)

thermal energy moving from an area of high temperature to an area of low temperature

ΔU in ΔU=Q - W (thermal physics)

change in internal energy

Q in ΔU=Q - W (thermal physics)

Heat added to system

W in ΔU=Q - W (thermal physics)

work done by the gas

condition for bodies to be in thermal equilibrium (thermal physics)

they are the same temperature

what happens when a gas does work (thermal physics)

expands

what happens when work is done on a gas (thermal physics)

contracts

clockwise cycle on a graph gives (Q and W) (thermal physics)

positive Q and W

anticlockwise cycle on a graph gives (Q and W) (thermal physics)

negative Q and W

specific heat capacity (thermal physics)

the amount of thermal energy needed to raise the temperature of 1kg of material by 1K

Binding Energy (nuclear energy)

work done on a nucleus to completely separate it into its neutrons and protons

Mass defect (nuclear energy)

mass lost when energy released

U- unified atomic mass unit

1/12 mass of carbon 12 atom

n (thermal physics/kinetic theory)

number of moles

N (thermal physics/kinetic theory)

number of molecules