Physics All Y9 Notes & Flashcards [end of years revision]

Energy, Waves, Motion

Where is chemical energy stored

food, fuel, batteries

Where is kinetic energy stored

moving objects

Where is thermal energy stored

hot objects

Where is strain/elastic energy stored

stretched, squashed, twisted materials

Where is atomic/nuclear energy stored

atoms

Where is gravitational energy stored

objects in high places

System

something in which we are studying changes

Law of conservation of energy

energy can’t be created or destroyed

Units for energy

Joules (J)

Sankey diagram

shows the amount of energy transferred and where to

Energy transfer diagram

shows energy stores and transfers

Dissipated

spread out into the surroundings

How do mechanical processes become wasteful

when they cause a rise in temperature - energy dissipates through heating to the surroundings

Energy efficiency definition

how good a machine is at transferring energy into useful forms

given in a number between 0 and 1 or a percentage

Energy efficiency formula

useful energy transferred by device

total energy supplied to device

How can you reduce friction

lubrication - making a surface smooth so things can move easily on it

Insulation

slows the pace at which energy is transferred out of a place

Conduction

vibrations passed between particles in a solid

Convection

part of a fluid is warmer (less dense) and rises up, on the other side it is colder (more dense) and sinks down.

this creates a convection current going round in a circle

Radiation

energy transferred through waves, some types (infrared) can pass through solid objects

Thermal conductivity

how well a material allows heat to move through it

can depend on thickness and temperature difference

a good insulator needs low thermal conductivity

Solar energy

heating and lighting from the sun used with solar panels

Wind energy

using wind turbines, kinetic energy of wind turns a turbine

Hydroelectric energy

flowing water turns a turbine

Wave energy

kinetic energy of sea’s waves turned into electricity

Nuclear energy

energy in uranium nuclei is transferred into heating, creates steam and turns a turbine

Fossil fuels

chemical energy in coal, oil, gas transferred into heating, creates steam and turns a turbine

Biomass energy

chemical energy in things that were once alive burned and turned into heating

Geothermal energy

rocks underground are very hot, heat produces steam which turns a turbine

Tidal energy

water trapped behind a dam at high tide is released, turning a turbine

Wave definition

an oscillation (vibration) that transfers energy and information (not matter) from one place to another

Wavelength definition

length of a full cycle e.g. crest to crest

Amplitude

size of wave (1/2 crest to trough)

Frequency definition

number of complete waves to pass a point per sec

Period definition

time taken to move through one complete cycle

Velocity definition

speed in a stated direction

wave speed (with frequency and wavelength)

speed = frequency x wavelength

Transverse wave

Vibrations are perpendicular to direction of transfer

Longitudinal wave

Vibrations are parallel to direction of transfer

Crest

highest point of wave

Trough

lowest point of wave

Equilibrium

middle point of wave

Wavefront

all locations where wave is in the same phase e.g. all troughs

Period equation

1 / frequency

Frequency equation

1 / period

Reflection

when a wave bounces off a surface at an angle and changes direction

Refraction

when light changes speed between different media

Transmission

when a wave passes through a material

Absorption

when a wave is taken in and the energy is transferred to the material

Refraction: when the wave gets faster…

it bends away from the normal

Refraction: when the wave gets slower…

it bends towards the normal

Range that humans can hear

20Hz - 20,000Hz

Ultrasound definition

very high sounds humans can’t hear above 20,000Hz

Infrasound

very low sounds humans can’t hear below 20Hz

Auditory nerve

electrical signals carry messages along this to the brain

Eustachian tube

tube that connects ear and nose

Ear canal

tube that carries sound to the inner ear

Pinna

visible part of the ear, collects sound waves and funnels them into the ear

Eardrum

thin membrane that vibrates when sound waves hit it

Ossicles

made up of the stirrup, anvil and hammer

they help transmit vibrations to the inner ear

Semi-circular canals

help you balance

Cochlea

snail shaped and full of cilia (tiny hairs) that convert vibrations into electric signals (aka nerve impulses)

The base is thicker and stiffer than the apex, and vibrates at higher frequencies.

Measuring waves in a ripple tank practical

1. Count how many waves are formed in 10secs

2. Put a ruler against the tank and use it to measure the length of the waves (easier to take a photo and measure off that)

3. Measure the distance between two points and see how long it takes waves to go from one part to another

To get frequency divide the number of waves in 10s by 10 (step 1)

To get speed divide the distance by the time (both from step 3) OR Multiply the wavelength (step 2) by frequency (above)

Ultrasound sonar

1. Ship emits ultrasound wave downwards

2. Wave reflects off seabed and returns to the ship

3. Speed = distance/time is used to calculate depth of seabed (distance) as instruments on the ship measure the speed & time of the wave

Ultrasound scanning

Transducer (or probe) is placed against skin

Gel is used to stop waves reflecting off skin

Transducer emits ultrasound waves and measures how long it takes for them to bounce off something and come back

Shorter time = closer object

Speed = distance/time used for exact distance calculations

An image can also be made if you know how far away lots of things are

P waves

longitudinal waves, travel through both solids and liquids

S waves

transverse waves, only travel through solid

Infrasound and the earth’s core

The properties of the earth change as you go deeper

The S wave shadow zone means that there is something liquid in the centre of the earth stopping the S waves going through, as they can’t travel through liquids (the mantle)

When P waves pass in and out of the liquid mantle, the refract and change direction

The few weak waves received in the P wave shadow zone are because of the solid inner core

This happens no matter where the earthquake is

Seismic waves

waves produced by earthquakes

Seismometers

instruments that detect/measure seismic waves

Scalars

Have just a magnitude (size)

Examples:
Speed
Distance
Time
Mass

Speed with distance & time

distance / time

Velocity equation

displacement / time

Acceleration definition

rate of change of velocity (doesn’t have to be getting faster)

Acceleration equation with time

a = acceleration
t = time
u = starting velocity
v = ending velocity

Acceleration in a free fall

10m/s²

Instantaneous speed

speed at any given moment throughout the journey

Average speed

speed averaged taking into account the whole journey

Gradient on a distance/time graph

speed

steeper gradient = more speed

Straight line on a distance/time graph

constant speed

Horizontal line on a distance/time graph

stationary

aka constant speed of 0

Area bounded on a distance/time graph

no meaning

Gradient on a velocity/time graph

acceleration

line sloping up = acceleration

line sloping down = deceleration (negative acceleration)

Straight line on a velocity/time graph

constant acceleration

Horizontal line on a velocity/time graph

constant velocity

Area bounded on a velocity/time graph

Distance travelled

Gradient equation

rise / run

1. Pick two points on a line

2. Find the vertical distance between points (rise)

3. Find the horizontal distance between points (run)

4. Divide the rise by the run

Example of a longitudinal wave

sound wave

Example of a transverse wave

Visible light wave