energy transfers (paper 1)

what is meant by a system

a set of things working together as parts of a mechanism or an interconnecting network

what is a closed system

a system where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always 0

when a system changes what happens

energy is transferred

energy can be transferred between stores in 4 main ways

• mechanically

• electrically

• by heating

• by radiation

energy names

• magnetic

• kinetic

• heat

• light

• gravitational

• chemical

• nuclear

• sound

• electrical

• elastic

energy

• energy is the ability to do work

• energy can be stored and transferred

• measured in joules

• energy is a scalar - it has no direction

work done = energy transferred

both measured in joules

forces

forces are vectors and are measured in newtons

some examples are:

• weight

• air resistance

• thrust

• reaction/normal contact

• tension

• drag

• upthrust

• lift

• push

• pull

• friction

work done (J) =

force (N) x distance moved (M)(moved in the direction of the force)

what is work done

the energy transferred when a force moves an object a certain distance (in direction of force)

if a force dosent move no work is done

if the force is bigger, more work will be done

if the force has moved a longer distance, more energy is transferred

1 joule is the work done when a force of 1 newton moves 1 meter

examples of work being done

a) driving a car - energy provides a driving force that does work on the car and it gains kinetic energy

b) lifting an object - i provide a force (equal to the weight) to lift an object and so i do work on the object and it gains GPE

c) firing a bow and arrow - the stretched bow exerts a push force and work is done on the arrow and it gains both EPE and KE

d) winding a clockwork toy - i exert a push force on the turning mechanism and do work on the spring inside so it gains EPE

e) meteorite falling to earth - the meteorite falls through the air and the air resistance acts against its motion so the meteorite gains thermal energy.

power

the RATE of doing work or energy transfer

examples to illustrate the definition of power

weight lifting

car engines

light bulbs

kinetic energy

ke is possesed by moving objects and depends on mass and velocity

KE = 0.5 X MASS X (VELOCITY)² = 1/2MV²

if there is a certain resultant force on an object it will accelerate and the KE will change. The force has done work on the object

snail KE

small mass and low speed so low ke store

car KE

large mass and high speed so large KE store.

gravitational potential energy

GPE is the energy posessed by an object due to its position above ground.

GPE = MASS X GRAVITY X HEIGHT

gravity = gravitational field strength

so gpe = weight x height (same as force x distance)

weight = mass x gravity

when i lift an object, i use a force equal to the weight and i do work. The work done = change in gpe

what is the gravitational field strength on earth

10 N/Kg

conservation of energy

• if we ignore friction, then when an object falls ALL the gpe lost = KE gained

I can describe the conservation of energy, with reference  to transfer, storage, dissipation, creation and destruction.

The conservation of energy is a principle stating that energy cannot be created or destroyed, only transformed or transferred. Energy can be transferred between systems (e.g., kinetic energy from a moving ball to a stationary one) and stored in various forms (like chemical energy in batteries or potential energy in elevated objects). During these processes, some energy may be dissipated as heat due to friction, leading to inefficiencies. While energy can change forms (e.g., chemical to mechanical in engines), it is essential to recognize that this is not the creation of new energy but rather a transformation. Destruction of energy occurs when it is converted into forms that are not useful for doing work, such as when energy is lost as heat. Overall, the total energy in a closed system remains constant.

how do energy transfers in a closed system  affect the total energy of the system.

they dont affect it at all

how is energy is dissipated when a system changes.

when it spreads out and is transferred into less useful, often wasted, forms, typically thermal energy (heating) or sound, rather than the intended output

e.g. Mechanical Friction: When a car brakes, kinetic energy is dissipated into the surroundings as heat via brake pads rubbing against wheels.

conservation of energy - roller coaster example

on a roller coaster, at point a you have max gpe (ignore friction), then all of this is transferred to KE at point b.

conservation of energy - throwing a ball up example

it starts with max ke and min gpe. at the top its all transferred to gpe. inbetween, the sum of gpe+ke = initial ke max

elastic potential energy

EPE energy = 0.5 x spring constant x extension

spring constant = J/M

extension = M

EPE = J

what is a spring constant

a measure of how stiff a spring is

what is extension

change in length (this can be compression as well)

specific heat capacity

SHC is the amount of energy needed to raise the temp of 1kg of a substance by 1 degree celcius

equation- change in thermal energy = mass x shc x temp change

rearranged - shc = change in thermal energy / mass x temp change

required prac - investigating specific heat capacity

Make this setup, measure the block of mass, and wrapit in an insulating layer to reduce energy transferred from the block to the surroundings.

create a circuit with these three componets: heater, power supply and ammeter

measure the initial temp of the block and set the pd of the power supply to be 10. Turn the power supply on and start a stop watch. as the block heats up, take readings of the temp and current every min for 10 mins. Keep an eye on the ammeter, the current through the circuit shouldnt change.

when you turn the power on, the current in teh circuit does work on the heater, transferring energy electrically from the power supply to the heaters thermal energy store. This energy is then transferred to the materials energy store by heating causing the materials temp to increase.

Using your measurement of the current and pd of the power supply, you can calc the power of the heater using p=ixv and you can use this to work out how much energy has been transferred by the heater at the time of each temp reading using e=pxt.

conduction

the process by which vibrating particles transfer energy to neighbouring particles. they vibrate and spread thermal energy until it is evenly spread out.

what is thermal conductivity

a measure of how quickly energy is transferred through a material in this way.

convection

convection is where energetic particles move away from hotter to cooler regions

it can happen in liquids and gases but does not tend to occur in solids. convection only occurs mainly in solids because the particles in liquids and gases are much more free to move around so their particles collide less frequently

because liquids and gases can flow, the warmer and less dense reigon will rise above denser, cooler reigons. If there is a constant transfer of energy by heating a substance, a convection current can be created where the air in the room circulates as reigons of it heat up and rise then cool down and fall.

efiiciency

ways to increase efficiency of an intended energy transfer

lubrication

insulation

streamlining - smoother shape reduces air resistance

reducing electrical resistance - use components with lower resistance in circuits

thermal insulation

the thicker the walls of a house and the lower their thermal conductivity, the slower the rate of energy transfer will be. You can help the amount of energy lost from a building using thermal insulators. Some examples are:

• cavity walls and cavity wall insulation - the air gap reduces the amount of energy transferred through the walls because air is an insulator

• loft insulation - it is made of fibreglass which reduces the energy transfer by convection, preventing convection currents from forming

• double glazing - air gap prevents conduction from transferring energy

• draught proofing - strips of foam around doors which reduces energy transfer by convection

• hot water tank jacket - fibre glass wool around a water tank which reduces energy transferred by conduction.

required prac - investigating reducing energy transfers

pour boiling water into a beaker and measure the initial temp

wrap in an insulating material and leave for 5 mins

measure the temp after and compare results

lubrication

whenever something moves, there is always at least one frictional force acting against it. This causes some energy in the system to be dissipated

for objects that are being rubbed together, lubricants can be used to reduce the friction between the objects surfaces when they move. lubricants are usually liquids (oil) so they can flow easily and coat the whole object.

it is a way of reducing unwanted energy transfers

rearranging the formula for elastic potential energy

EPE = ½ x spring constant x (extension)²

spring constant = (2 x EPE) / extension ²

extension = √((2xEPE)/spring constant)

rearranging formula for gravitational potential energy

GPE = mass x grav field strength x height

mass = gpe / (height x grav field strength)

height = gpe / (mass x grav field strength)

rearranging formula for specific heat capacity

shc = change in thermal energy / (mass x temp change)

mass = change in thermal energy / (shc x temp change)

temp change = change in thermal energy / (mass x shc)