GCSE Physics Paper 1 (copy)

1hr45, 100 marks, 50% of GCSE. Key concepts of phsics, Motion & forces, Conservation of energy, Waves, Light & the EM spectrum, Radioactivity, Astronomy

prefixes

scalars

quantities that only have a magnitude not direction e.g. mass & distance

vectors

quantities that have both magnitude & direction e.g. velocity (need to mention both speed & direction)

distance is a scalar quantity while displacement is a vector quantity as it has direction

scalar & vector examples

distance & displacement

distance = how far an object travels (scalar)

displacement = the distance of an object from its starting position + its direction (vector)

speed + equations

the distance an object travels every second (scalar)

speed (m/s) = distance travelled (m) / time taken (s)

average speed = total distance / time taken

velocity

the speed of a moving object with its direction - vector e.g. 15m/s south

distance-time graphs

shows how the distance of an object moving in a straight line from a starting position varies over time. shows if an object is moving at a constant speed and how big / small the speed is

straight line = constant speed

slope of line = magnitude of speed. steep slope = large speed, shallow slope = small speed, flat horizontal line = stationary

changing speed = curve. slope increasing = accelerating, slope decreasing = decelerating

speed can be calculated from the gradient of a line - rise/run or Δy/Δz. use the whole line to calculate gradient

acceleration

the rate of change of velocity aka how much an object’s velocity changes every second

a = Δv / t
acceleration (m/s²) = change in velocity (m/s) / time taken (s)

Δv = v - u
change in velocity = final velocity - initial velocity

the acceleration of an object can be positive or negative depending on whether the object is accelerating or decelerating

speed of acceleration due to gravity

10m/s²

typical accelerations

uniform acceleration (equation)

applies to objects moving with uniform (constant) acceleration:

v² - u² = 2ax
final speed² (m/s) - initial speed² (m/s) = 2 x acceleration (m/s²) x distance travelled (m)

useful for where time isn’t known

velocity-time grapha

shows how the velocity of a moving object varies with time. shows if the object is moving with a constant acceleration / deceleration & the magnitude of this

straight line = constant acceleration

slope of line = magnitude of acceleration. steep = large, gentle = small

a flat line = 0 acceleration - constant speed

acceleration can be calculated using gradient - rise/run or Δy/Δx

area under a velocity-time graph = displacement / distance travelled by object. break it up into shapes & calculate the area

typical speeds table

(but these things do depend on factors e.g. age / fitness, type of car)

simple measuring falling speed practical

compare average falling speed of objects e.g. tennis ball, plastic cone:

• metre rule used to measure distance they fall from

  • or a tape measure / trundle wheel for larger distances

• timer used to measure how long they take to reach the ground

measuring speed using light gates practical

light gates are pieces of digital equipment that allow times to be measured more accurately. they can be used to start / stop a timer when an object passes through - flags on top of moving object blocks beam of light as it passes through the light gate

a single light gate can be used to measure speed:

• timer measures how long light gate is blocked by flag for

• distance = length of flag

• speed calculated through speed = distance / time

newton’s first law of motion

objects will remain at rest or move with a constant velocity unless acted on by a resultant force

so if an object is at rest / constant velocity there are no resultant forces acting on it

newton’s second law

the acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the object’s mass

aka an object will accelerate (change velocity) in response to a resultant force. the bigger the resultant force, the larger the acceleration. but the bigger the object’s mass, the smaller the acceleration

force & acceleration equation (newton’s second law)

F = ma
force (N) = mass (kg) x acceleration (m/s²)

investigating force & acceleration practical - experiment 1: investigating the effect of force on acceleration

aim - invesetigate the effect of varying force on the acceleration of an object of constant mass

independent variable = force, dependent variable = acceleration, control variable = mass

1. use ruler to measure out intervals on bench & mark out with pencil / chalk

2. attach bench pulley to end of bench

3. tie string to toy car / trolley & pass it over the pulley. attach the mass hanger to the other end. make sure the string is horizontal & in line with the trolley

4. hold the trolley at start point & attach the full set of weights to the end of the string

5. release the trolley & start the stopwatch. press the stopwatch in lap mode at each measured interval on the bench until the end

6. repeat to calculate an average time & record results in a table

7. repeat with decreasing weights. place masses you remove from the weight stack onto the top of the trolley using blue tac

use results table to determine average speed of trolley in different intervals (s=d/t) & compare the speeds between the first & last intervals. calculate the acceleration between first & last intervals (a=Δv/t)

systematic errors - ensure any weight removed from hanger are transferred to car to ensure total mass of system remains constant

random errors - take repeat readings of time to keep timing errors to a minimum. start the car by releasing it, don’t give it a push

safety - don’t stand under the weight hanger in case any weight fall. place a crash mat under the hanger in case this happens

independent variable

the variable you change, unaffected by other variables

dependent variable

the variable you measure, dependent on other varaible

investigating force & acceleration practical - experiment 2: investigating the effect of mass on acceleration

aim = investigate the effect of varying mass on the acceleration of an object produced by a constant force

independent variable = mass, dependent variable = acceleration, control variables = force

1. use ruler to measure out intervals on bench & mark out with pencil / chalk

2. attach bench pulley to end of bench

3. put a 200g mass on car

4. tie string to car & pass it over the pulley & attach the mass hanger to the other end. make sure string is horizontal & in line with the car

5. put a weight on the weight hanger that will gently accelerate the car along the bench

6. hold the car at the starting point

7. release the car & start the stopwatch. lap the stopwatch at each measured interval

8. repeat to find average & record results in a table

9. repeat with increasing masses

calculate average speed intervals (s=d/t) & compare average speed between first & last intervals for different weights. calculate acceleration between first & last intervals (a=Δv/t)

random errors - take repeat readings of time to keep timing errors to a minimum. start the car by releasing it, don’t give it a push

safety - don’t stand under the weight hanger in case any weight fall. place a crash mat under the hanger in case this happens

how to answer questions about practicals

• If you need to use an equation to calculate something, start off by giving it as this will give you some hints about what you need to mention later

• List the apparatus that you need

• State what measurements you need to make (your equation will give you some hints) and how you will measure them

• Finally, state that you will repeat each measurement several times and take averages

newton’s third law

describes the effects of the forces involved when 2 different objects interact with each other

Whenever two bodies interact, the forces they exert on each other are equal and opposite 

force pairs = the pair of forces exerted by the interacting objects

e.g. when walking:

• two objects interacting = foot & ground

• foot exerts push force on ground

• ground exerts push force on foot

• the forces are equal in magnitude & opposite in direction

how to identify newton’s third law

the two forces are:

1. acting on different objects

2. equal in size

3. acting in opposite directions

4. the same type (weight, reaction force etc)

you can describe forces as a push/pull force if you don’t know the name

weight

the force acting on an object due to gravitational attraction

planets have strong gravitational fields so they attract nearby masses using gravitational force

because of weight objects stay on the ground, will always fall to the ground, and satellites are kept in orbit

weight equation

W = mg
weight (N) = mass (kg) x acceleration due to gravity on earth (9.81 N/kg or ms^-2)

weight and mass

the weight that an object experiences depends on the object’s mass and the mass of the planet attracting it (w = mg)

mass is measured in kilograms and is related to the amount of matter in an object

weight is measured in newtons and is the force of gravity on mass

the weight & mass of an object are directly proportional, and the size of weight depends on the gravitational field strength

weight is a force so it’s a vector quantity. mass is an amount so is a scalar quantity

measuring weight

mass is commonly measured with a top pan balance and then weight is found using w = mg

weight can also be measured directly using a newton-meter, a type of weighing scale that measures force in newtons. it consists of a spring fixed at one end with a hook to attach an object at the other

weight and gravity - weight on different planets

the strength of gravity on different planets alter an object’s weight on that planet

an object’s mass will always stay the same but its weight will change depending on the strength of the gravitational field on different planets

gravitational field strength varies from planet to planet depending on their mass and radius. planets’ strong gravitational fields attract nearby masses, meaning objects stay firmly into ground & will always fall to the ground, and satellites are kept in orbit

circular motion

because velocity is a vector, when an object travels in a circle its velocity is always changing, even if the speed is the same, because the direction is always changing

this means an object moving in circular motion travels at a constant speed but has a changing velocity

centripetal force

an object moving in a circle isn’t in equilibrium as it has a resultant force acting on it. this force is centripetal force and is what keeps the object moving in a circle.

centripetal force (F) = the resultant perpendicular force towards the centre of the circle required to keep a body in uniform circular motion

it’s always perpendicular to the direction of travel and is directed towards the centre of the circle

due to newton’s second law, centripetal force and centripetal acceleration act in the same direction

centripetal force isn’t a separate force of its own - it can be any type of force depending on the situation for example:

• car going round a roundabout = friction between car tires & road

• bell attached to rope moving in a circle = tension in the rope

• earth orbiting the sun = gravitational force

momentum equation

p = mv
momentum (kg m/s) = mass (kg) x velocity (m/s)

momentum

a moving object has momentum, but if it’s at rest it has no momentum. it’s measured in kg m/s

momentum keeps an object moving in the same direction - it’s hard to change the direction of an object with a large momentum

because velocity is a vector the momentum of an object depends on the direction of travel. so it can be either positive or negative. generally right & up are positive and down & left are negative but its up to you

the momentum of an object will change if:

• the object accelerates / decelerates

• the object changes direction

• the mass of the object changes

momentum in collisions

elastic collision - when objects collide and move in opposite directions
each object has a different velocity depending on its mass & initial momentum

inelastic collision - when objects collide and move in the same direction together
the 2 objects will have a combined mass & velocity

momentum is always conserved in a collision

what to do in questions that ask you to analyse a collision

1. consider the motion before & after the collision. state the velocities of each object and the direction each moves in

2. state whether the collision was elastic or inelastic & explain your reasoning (do they stick together or not?)

3. describe any energy transfers that occur if kinetic energy isn’t conserved e.g. it may be converted into heat, sound, elastic potential energy etc

conservation of momentum

principle of conservation of momentum - in a closed system the total momentum before an event = the total momentum after the event

closed system = energy in system is constant + no external forces like friction

aka total momentum before collision = total momentum after collision

since momentum is a vector, objects moving in opposite directions (eg towards each other) have an overall momentum of 0 as they cancel each other out

newton’s 3rd law

when 2 bodies interact the forces they exert on each other are equal & oppsite

this means when object 1 exerts a force on object 2, object 2 will exert an equal force on object 1 in the opposite direction

when 2 objects collide they will both react

change in momentum equation

Δp = mv – mu
change in momentum = (mass x final velocity) - (mass x initial velocity)

can also be written as final momentum - initial momentum

inertia

the tendency of an object to continue in its state of rest or in uniform motion unless acted upon by an external force - aka an object’s resistance to change in motion

if an object’s at rest it will tend to remain at rest, and if it’s moving at a constant velocity it will continue to do so

inertial mass

how difficult it is to change an object’s velocity. the ratio between the force applied and the acceleration it experiences:

m = F / a
inertial mass (kg) = force (N) / acceleration (m/s²)

this equation shows that for a given force inertial mass is inversely proportional to acceleration.

stopping distance

the total distance travelled during the time it takes for a car to stop in response to some emergency

stopping distance = thinking distance + braking distance

thinking distance: the distance travelled in the time it takes the driver to react (reaction time)
braking distance: the distance travelled under the braking force

for a given breaking force, the greater the speed of the vehicle, the greater the stopping distance

all are measured in meters

dangers on the road: overheating of breaks

the breaks of a vehicle reduce its speed by creating a friction force between the brake and the wheel

the kinetic energy of the vehicle is converted to the thermal energy of the breaks

if the breaks get too hot they can fail, meaning they won’t work effectively next time they’re used

dangers on the road: loss of control and injury

when a vehicle undergoes a deceleration the driver & passengers also experience a deceleration

this can cause injuries like whiplash - a neck injury caused when a person’s head moving suddenly, relatively to the body

it’s also more difficult to control a vehicle that’s decelerating. losing control can cause a collision

reaction time

a measure of how much time passes between seeing something and reacting to it

the human reaction time for someone who is alert (waiting for something to happen) is usually ~0.2 - 0.9 seconds

measuring reaction time

• person A holds a 30cm ruler vertically so the bottom hovers over the top of the hand of person B

• person A releases the ruler unexpectedly

• as soon as person B sees the ruler move they close their hand to catch it

• the ruler is marked at the point at which it was caught by person B, giving the measurement of the distance the ruler fell

greater distance = longer reaction time

braking distance

the distance travelled by a car under the breaking force - while it’s slowing down

the main factor affecting braking distance is the car’s speed - the greater the speed, the greater the breaking distance. other factors include:

• vehicle condition - eg worn tires or poor brakes

• road condition - wet/icy roads make it harder to decelerate (smoother road = less friction between tyres and road)

• vehicle mass - a heavy vehicle (eg a lorry) takes longer to stop

the braking distance is the ratio of the kinetic energy of the car and the braking force. (this is because the work done in bringing a car to rest is the transfer of all its kinetic energy into other forms eg thermal, sound)

as KE = ½mv², braking distance is proportional to velocity squared. so if the velocity doubles the braking distance increases by 2² or 4 times

thinking distance

the distance travelled by a car from when a driver realises they need to brake to when they apply the brakes

reaction distance = speed of car x driver’s reaction time

main factor that affects thinking distance is the car’s speed but additional factors include tiredness, distractions (eg mobile phone), and intoxication (eg consumption of alcohol/drugs)

estimating stopping distances

for a given force, the speed of a vehicle determines the size of the stopping distance. greater speed = larger stopping distance

calculating braking distance

when a vehicle stops its kinetic energy is transferred to the thermal energy in the brakes, which does work

braking force x braking distance = ½ x mass x velocity²
braking force x braking distance = work done by brakes
½ x mass x velocity² = kinetic energy of the car

this equation shows that the work done is the transfer of kinetic energy. we can use it to estimate the decelerating forces required for a typical vehicle moving at everyday speeds. the equation can be rearranged to show how the braking distance depends on velocity:

braking distance = ½ x mass x velocity² / braking force

this equation shows that the braking distance is proportional to the vehicle’s velocity squared. however at very high speeds it doesn’t apply because the brakes get hot & become less effective, reducing braking force & causing the braking distance to increase.

gravitational potential energy + equation

energy in the gravitational store of an object = the energy an object has due to its height in a gravitational field

if an object is lifted up, energy is transferred to its gravitational potential store. if it falls, energy is transferred away from its gravitational potential store

ΔGPE = m x g x Δh
change in gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x change in vertical height (M)

gravitational field strength on different planets

g on earth is approx 10 N/kg. the gravitational field strength on the moon is less than on earth, meaning it’s easier to lift a mass on the moon than on earth. g on gas giants (eg jupiter & saturn) is more than on earth.

kinetic energy + equation

the amount of energy an object has as a result of its mass and speed. any object in motion has energy in its kinetic store

KE = ½ x m x v²
kinetic energy (J) = ½ x mass (kg) x speed of object² (m/s)

closed systems

system = a certain number of objects under consideration. a way of narrowing the parameters to focus on only what’s relevant

when a system is in equilibrium, nothing changes & nothing happens. when there is a change in a system, energy is transferred

closed system = a system where there is no net change to the total energy in that system. the total amount of energy in the system remains constant (due to conservation of energy)

conservation of energy

principle of conservation of energy - energy can’t be created or destroyed, it can only be transferred from one store to another. this means the total amount of energy in a closed system stays constant

total energy transferred into a system must = total energy transferred out

so energy is never lost but it can be transferred to the surroundings - dissipated (spread out) to the surroundings by heating & radiation. dissipated energy transfers are often not useful & can be described as wasted energy

energy stores

energy is stored in objects in different energy stores

• kinetic - moving objects

• gravitational - when objects are lifted above ground

• elastic - when objects are stretched

• electrostatic - objects with charge interacting with each other

• magnetic - magnetic materials interacting with each other

• chemical - objects can release energy in chemical reactions

• nuclear - when atomic nuclei release energy during nuclear reactions

• thermal - all objects have energy in thermal store (hotter object = more energy)

energy transfers

energy is transferred between stores via transfer pathways:

• mechanical working - when a force acts on an object eg pulling, pushing, stretching

• electrical working - a charge (current) moving through a potential difference eg charge around a circuit

• heating by particles - energy transferred from a hotter object to a colder one

• heating by radiation - energy transferred by electromagnetic waves eg light

energy flow diagrams

energy stores & transfers can be represented using a flow diagram, which shows the stores & transfers within a system

sankey diagrams

can be used to represent energy transfers using splitting arrows that show the proportions of the energy transfers taking place

left hand side of the arrow (flat end) = energy transferred into system
straight arrow pointing to the right = energy that ends up in desired store (useful energy output)
arrows that bend away = wasted energy

the width of each arrow is proportional to the amount of energy being transferred

example energy transfers: an object propelled upwards

when the person holds the ball they have energy in their chemical store

when the ball is thrown some of that energy is transferred to the kinetic store of the ball as it begins to move upwards

as the height of the ball increases, energy from the kinetic store of the ball is transferred to its gravitational potential store

example energy transfers: moving object hitting an obstacle

if an object (like a car) hits an obstacle (like a wall) the speed of the car decreases very quickly, and the energy in its kinetic store decreases too

in this scenario most of the energy in the kinetic store is dissipated (transferred to the thermal store of the surroundings), transferred mechanically to the thermal store of the wall (for of the car on the wall), and transferred by heating to the thermal store of the air as sound waves transfer energy away from the system

example energy transfers: vehicle being accelerated by a constant force

when an object like a vehicle is stationary it has energy in the chemical store of the fuel. when it accelerates, energy is transferred to the kinetic store of the car

example energy transfers: vehicle slowing down

when a vehicle is moving it has energy in its kinetic store

as it decelerates energy is dissipated (transferred to the thermal store of the surroundings) by heating due to friction between the tyres & ground and between the brakes & brake pads, and by heating as sound waves transfer energy away from the system

example energy transfers: boiling water in an electric kettle

when an electric kettle boils water energy is transferred electrically from the mains supply to the thermal store of the heating element in the kettle

as the heating element gets hotter energy is transferred by heating to the thermal store of the water

example energy transfers: trampoline

when jumping a person has energy in their kinetic store. when they land on the trampoline most of that energy is transferred to the elastic potential store of the trampoline. it’s then transferred back to the kinetic store of the person as they bounce up

energy is transferred from the person’s kinetic store to their gravitational potential store as they gain height

some energy is dissipated by heating to the thermal store of the surroundings (person, trampoline, air)

the useful energy transfers are elastic potential energy → kinetic energy → gravitational potential energy

useful vs wasted energy

mechanical processes can become wasteful when they cause a rise in temperature, often when friction is involved. friction transfers energy from the kinetic store by heating to the objects & surroundings - aka dissipated (spread out). this energy can’t be used in a useful way so is called wasteful.

useful energy = an energy transfer that serves an intended purpose

wasted energy = an energy transfer that’s not useful for the intended purpose and is dissipated to the surroundings

dissipation of energy

energy transferred by heating & radiation have a tendency to spread out to the surroundings - this is dissipation

dissipated energy is hard to ‘gather’ to be used again, so becomes less useful. whenever a process produces unwanted heat / light / sound the energy is dissipated and essentially wasted

however not all dissipated energy is wasted, for example:

in a tv the useful energy transfer is when energy is transferred electrically from the mains supply and is dissipated to the surroundings by radiation as visible light & by heating as sound waves

in a heater, the useful energy transfer is when energy is transferred electrically from the mains supply to the thermal store of the heating element & then dissipated to the surroundings by heating

reducing energy loss

there are many situations where energy transfers are unwanted e.g. keeping a house/drink warm/cold or reducing friction of mechanical parts

when an appliance is used for heating it uses a lot of energy, which can become expensive and produces greenhouse gases. so it’s useful to find ways of reducing unwanted electricity transfers

energy that’s dissipated to the surroundings is often the main source of wasted energy transfers

if unwanted energy transfers can be prevented or reduced the useful energy transfers can be made more efficient

reducing energy loss: lubrication

friction is a major cause of wasted energy transfers - eg the gears on a bike become hot if they’re used for a long time. energy is transferred wastefully from the kinetic store of the bike to the thermal store of the gears & chain, meaning the person has to do more work to make the bike move as less energy is being transferred usefully

this wasted energy transfer can be reduced if the amount of friction is reduced. this can be done by lubricating the parts that rub together

reducing energy loss: insulation

reduces energy transfers from conduction. the effectiveness of an insulator depends on the material’s:

• thermal conductivity: lower conductivity = less energy transferred

• density: denser = more conduction can occur. in a denser material the particles are closer together so they can transfer energy to one another more easily

• thickness: thicker = better insulator

insulating houses lowers its rate of cooling meaning less energy is transferred outside. the insulation is usually made of fibreglass, a reinforced plastic composed of woven material with glass fibres laid across. the air trapped between the fibres makes it a good insulator

cavity wall insulation: when gaps or cavities between external walls are filled with insulation. often done by drilling a hole through the external wall to reach the cavity & filling it with foam made from blown mineral fibre filled with gas. this lowers the conduction of heat through the walls

conduction of heat

thermal conduction: when heat is transferred by vibrating particles in a substance. the main method of energy transfer by heating in solids. metals are very good thermal conductors, non-metals are poor thermal conductors & gases are extremely poor - they are called insulators

the vibrating particles transfer energy from their kinetic store to the kinetic store of neighbouring particles. the direction of energy transfer is always from hot to cold

higher thermal conductivity of a material = higher rate of energy transfer by conduction across the material. materials with high thermal conductivity heat up faster than materials with low thermal conductivity

objects will continue to lose/gain heat until they reach thermal equilibrium (equal temp) with their surroundings

factors affecting thermal conduction

• thickness of the material

• thermal conductivity of the material

• temperature difference between the 2 areas of the material

you can reduce the rate of energy transfer by

• increasing the thickness of the material

• decreasing the thermal conductivity of the material

• decreasing the temperature difference

efficiency

the ratio of the useful energy output from a system to its total energy output. a measure of the amount of wasted energy in an energy transfer. can be represented as a decimal or percentage

high efficiency = most energy transferred is useful
low efficiency = most energy transferred is wasted

efficiency = useful energy transferred by device / total energy supplied to device

improving efficiency

you can improve the efficiency of a device by reducing wasted energy transfers

friction between moving parts in machinery leads to unwanted energy transfers by heating. you can reduce this by adding bearings to prevent components directly rubbing and lubricating parts

in circuits there is electrical resistance as current flows, resulting in unwanted energy transfers by heating. this can be reduced by using components with lower resistance and reducing the current

air resistance causes a frictional force between a moving object and the air, resulting in unwanted energy transfers by heating. this can be reduced by streamlining the shapes of objects

noise is often created by moving parts of machinery, leading to unwanted energy transfers by heating as sound waves cause particles to vibrate. this can be reduced by tightening loose parts to reduce vibration and lubricating parts

energy resources

large stores of energy that can be used to generate electricity and heat buildings. can be renewable or non-renewable

a turbine turns, which turns a generator, which generates electricity. the element that differs is how the turbine is made to turn

renewable energy resources

an energy source that is replenished at a faster rate than the rate at which it’s being used. this means the source won’t run out.

solar, wind, bio-fuel, hydroelectricity, geothermal, tidal

non-renewable energy resources

energy sources that are being replenished at a slower rate than they’re being used, meaning they will eventually run out. fossil fuels (coal, oil, natural gas) and nuclear fuel

energy from water

water can be used to turn turbines in hydroelectric dams, tidal barrages & tidal turbines

energy in the kinetic store of the flowing water → kinetic store of the turbine → kinetic store of the generator → transferred electrically to the national grid

energy from fossil fuels

fossil fuels can be combusted to heat water and the steam produced can turn turbines

energy from chemical store of fuel → thermal store of water → kinetic store of turbine → kinetic store of generator → transferred electrically to the national grid

energy from nuclear fuel

nuclear fuel can be used to heat water to produce steam to turn turbines

energy in nuclear store of fuel → thermal store of water → kinetic store of turbine → kinetic store of generator → transferred away electrically

energy from geothermal sources

geothermal energy is another way to produce the steam that turns the turbines. water is pumped down to the hot rocks and returns through a fissure as steam

energy in the thermal store of rocks → thermal store of water → kinetic store of turbine → kinetic store of generator → transferred away electrically

types of energy resources

fossil fuels are combusted to heat water to produce steam to turn turbines to generate electricity

nucelar fuels are reacted to heat water to produce steam to turn turbines to generate electricity

bio-fuels like plant matter, ethanol or methane can be produced and used as fuel to heat the water

wind turns turbines to generate electricity

in a hydroelectric dam water is stored at height and released to turn turbines

the tidal movement of water turns turbines

geothermal energy in hot rocks underground are used to heat the water

solar cells use light to generate electricity

moving water due to waves turns turbines

reliable vs non-reliable energy

a reliable energy resource can produce energy at any time

a non-renewable resource can only produce energy some of the time

comparing energy resources

energy resource	renewable?	advantages	disadvantages
fossil fuels	no	reliable, can produce lots of energy at short notice	produces greenhouse gasses & pollution
nuclear	no	reliable, no greenhouse gases or pollution, lots of energy from little fuel	produces radioactive waste that takes 1000s of years to decay
bio-fuels	yes	CO2 produced is balanced with CO2 absorbed while producing it	takes up lots of land & resources needed for food production
wind	yes	no greenhouse gasses / pollution, land can still be used	not reliable, can be noise & ugly, not everywhere is suitable
hydroelectric	yes	reliable, lots of energy at short notice, no greenhouse gasses / pollution	can involve flooding large areas & destroying wildlife habitats
tidal	yes	tides are predictable, lots of energy at regular intervals	very few suitable locations, cause environmental harm & distrust shipping
geothermal	yes	reliable, small stations	can release harmful gases from underground, not many suitable places
solar	yes	no greenhouse gases / pollution, good for remote places	not reliable, solar farms take up lots of land

use of energy resources: transport

most vehicles are powered by petroleum products like petrol, diesel & kerosene, which originate from crude oil, a fossil fuel

a growing number of vehicles are being powered by electricity, which produces 0 carbon emissions when driven but still uses the national grid to charge, which uses a mix of renewable & non-renewable energy

vehicles can also be powered by biofuel, a renewable resource. but the claim that biofuels are carbon-neutral is controversial

use of energy resources: electricity generation

demand for electricity is very high and all available energy resources are needed to keep up with it. most of the world’s energy is still produced by non-renewable, carbon-emitting sources. this has a negative impact on the environment

use of energy resources: heating

most homes in cold countries are fitted with central heating systems, which use natural gas to heat up water which can be pumped around radiators. but gas is a non-renewable energy resource

in geologically active countries (eg icleand) they can heat their homes using geothermal energy

waves

oscillations / vibrations about a fixed point. transfer energy and information. eg ripples causing particles of water to oscillate up & down or sound waves causing particles of air to vibrate back & forth

waves transfer energy without transferring matter

amplitude

the distance from the undisturbed position to the peak or trough of a wave

measured in meters, symbol A

on a graph where the vertical axis is displacement, the amplitude is from the undisturbed position (centre line) to either the highest point (peak) or lowest point (trough)

wavelength

the distance from one point on a wave to the same point on the next wave

in a transverse wave from one peak to the next. in a longitudinal wave from the centre of one compression to the centre of the next

measured in meters, symbol λ (lambda)

wave frequency

the number of waves passing a point in a second

measured in hertz (Hz), symbol f

wave time period

the time taken for a single wave to pass a point

measured in seconds, symbol T

determined by measuring the time from one point on the wave to the same point on the next one

frequency & period of a wave equation

f = 1 / T

frequency (Hz) = 1 / period (s)

wave speed

the distance travelled by a wave each second. the speed at which energy is transferred through a medium

wavefront

a way of picturing waves from above - each wave is represented by a single line

arrow (or ray) shows direction that the waves are moving

space between each wave front = wavelength. close together waves = short wavelength, far apart waves = long wavelength

transverse waves

waves where the points along its length vibrate at 90 degrees to the direction of energy transfer - energy transfer is perpendicular to wave motion

can move in solids and on the surfaces of liquids but not inside liquids or gases. some transverse waves (eg em waves) can move in solids, liquids & a vacuum

examples of transverse waves:

• ripples on surface of water

• vibrations on a guitar string

• s-waves (seismic waves)

• electromagnetic waves (eg radio, lights, x-rays)

drawing transverse waves

drawn as a single undisturbed line, usually with a central line showing the undisturbed position

curves are drawn perpendicular to the direction of energy transfer and represent peaks & troughs

longitudinal waves

waves where the points along its length vibrate parallel to the direction of energy transfer

energy transfer is in the same direction as wave motion. can move in solids, liquids & gases, but not in a vacuum (no particles)

points close together are compressions, points spaced apart are rarefactions

examples of longitudinal waves:

• sound waves

• p-waves (seismic wave)

• pressure waves caused by repeated movements in a liquid / gas

drawing longitudinal waves

drawn as several lines to show they’re moving parallel to the direction of energy transfer

close together lines represent compressions, far apart lines represent rarefactions