Physics - P1

energy stores + transfers, energy resources

what are the __eight__ energy stores?

* thermal
* kinetic
* gravitational potential
* elastic potential
* chemical
* magnetic
* electrostatic
* nuclear

how can energy be transferred?

* mechanically (force doing work)
* electrically (work done by moving charges)
* by heating
* by radiation (light, sound etc)

what happens when a system is changed?

(system is a single object/group of objects)

energy is __transferred__

(into or away from the system, between different objects in the system or different energy stores)

what are closed systems?

systems where __neither matter nor energy can enter or leave__

(the net change in the total energy of a closed system is always zero)

how can energy be transferred by heating?

water in a kettle:

energy is transferred electrically to the thermal component of the kettle, which transfers energy by heating to the water’s thermal energy store

what are examples of doing work?

* initial force of throwing a ball upwards (chemical - kinetic)
* gravitational force of dropping a ball (gravitational potential - kinetic)
* friction between car brakes + wheels as it slows down (kinetic energy - thermal in the surroundings)
* collision between car and solitary object (kinetic - other)

what has kinetic energy and what does this depend on?

* anything that is moving - energy is transferred TO this store when an object __speeds up__ and transferred AWAY when an object __slows down__
* the energy in the kinetic store depends on the object’s __mass + speed__ - greater the mass and the faster it’s going, the more energy there will be in this store

what has gravitational potential energy and what does this depend on?

* raised objects - lifting an object in a gf requires work, which -causes a transfer to the gpe store of the object (the higher the object is lifted, the more gpe it has)
* the energy in the gpe store depends on the object’s __mass, its height and the strength of the gravitational field__

what energy transfers happen when something falls?

gravitational potential energy store → kinetic energy store

energy lost from gpe store = energy gained in kinetic store (with no air resistance)

air resistance causes some energy to be transferred to other stores (e.g thermal)

what is specific heat capacity?

specific heat capacity is __how hard it is to heat something up__

(different materials have different specific heat capacities eg. water needs 4200J to warm 1kg by 1C but mercury only needs 139J)

REQUIRED PRACTICAL - investigating specific heat capacities

1. you will need a block of chosen material with two holes in it (for heater and thermometer to go in)
2. measure the mass of the block and wrap it in an insulating layer, then insert the heater and thermometer
3. measure the initial temperature of the block, set the voltage of the power supply to be 10V, then turn on the power supply and start the stopwatch
4. as the block heats up, take readings of the temp and current, every minute for 10 minutes
5. use P = VI to calculate the power supplied to the heater
6. calculate how much energy has been transferred to the heater using E = Pt (t is the time in seconds since it began)
7. plot a graph based on the results, and then find the gradient of the straight part (temp change / change in thermal energy)
8. the specific heat capacity of the material is 1/ (gradient x mass of the block)

what is the conservation of energy principle?

energy can be transferred usefully, stored or dissipated, but cn __never be created or destroyed__

what is power?

power is the __rate of energy transfer__, or the rate of doing work

power is measured in watts (one watt = one joule of energy transferred per second)

a powerful machine is one which transfers a lot of energy in a short space of time

what is conduction + where does it occur?

the process where vibrating particles transfer energy to neighbouring particles - occurs __mainly in solids__

(particles in an object being heated vibrate and collide with each other, causes energy to be transferred between particles’ kinetic energy stored - thermal conductivity is how quickly this happens)

what is convection + where does it occur?

where energetic particles move away from hotter to cooler regions - occurs __only in liquids and gasses__

(similar to conduction, but unlike in solids, particles in liquids and gases are able to move - when heated particles move faster and space between them increases, density decreases - warmer and less dense region will rise above cooler denser regions)

how can we reduce unwanted energy transfers?

* lubrication - reduces frictional forces
* insulation - reduces rate of thermal transfer

what is efficiency?

most energy transfers involve some waste energy - the __less energy that is wasted, the more efficient the device is__

useful energy output is not equal to total energy input as no device is 100% efficient (usual wasted energy → unwanted thermal stores)

what are non-renewable energy sources?

* fossil fuels - oil, coal, natural gas
* nuclear fuel - uranium, plutonium

these __will run out some day__ and do damage to the environment, but they are __reliable__

what are renewable energy sources?

* solar
* wind
* waves
* tides
* hydro-electricity
* biofuel
* geothermal

these __will never run out__, they do less damage to the environment but are __less reliable__ and don’t provide as much energy

wind, solar and geothermal resources

* wind - turbine that have a generator in them, the spinning blades generate electricity
* solar cells - depends on solar rays, so only can be used in the daytime
* geothermal power - uses underground thermal stores in volcanic areas (slow decay of radioctive elements) - reliable

hydro-electricity, waves and tides

* hydro-electricity - falling water in valleys using dams -
* waves - wave powered turbines
* tidal barrages - uses the sun and moon’s gravity

bio-fuels and non-renewables

* bio-fuels - made from plants and waste - large costs
* non renewables - reliable but cause environmental problems such as carbon dioxide released into the atmosphere when fossil fuels are burnt - nuclear waste is dangerous and potential major catastrophe