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 objet 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 (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 force

Resonance (SHM)

driving force of a oscillating system with a frequency that matches the natural frequency

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

Radioactive Atom (radioactivity)

atom with an unstable nucleus

alpha particle (radioactivity)

2 protons and 2 neutrons

helium nucleus

beta particle (radioactivity)

electron

gamma radiation (radioactivity)

high energy, high frequency electromagnetic wave

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 inn 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

Becquerel (Bq) (radioactivity)

one disintegration per second

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 and area of high temperature to an area of low temperature

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

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