Energy
combined science
- Created by: abbienoice
- Created on: 18-11-20 15:46
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- Energy
- energy stores and systems (object)
- energy stores
- thermal energy stores
- kinetic energy stores
- anything moving has energy in its kinetic store
- energy is transferred to this store when an object speeds up and is transferred away from this store when object slows down
- energy in the kinetic energy store depends on the objects mass and speed
- the greater its mass and the faster its going, the more energy there will be in its kinetic energy store
- gravitational potential energy store
- lifting an object in a gravitational field requires work - this causes a transfer of energy to the gravitational potential energy store of the raised object
- the higher the object is lifted the more energy is transferred to this store
- the amount of energy in this store depends on the objects mass, its height and the strength of the gravitational field the object is in
- when something falls, energy from the gravitational energy store is transferred to its kinetic energy store
- energy lost from the g.p.e store = energy gained in the kinetic energy store
- lifting an object in a gravitational field requires work - this causes a transfer of energy to the gravitational potential energy store of the raised object
- elastic potential energy stores
- stretching or squashing an object can transfer energy to the elastic potential energy store
- chemical energy stores
- magnetic energy stores
- electrostatic energy stores
- nuclear energy stores
- when a system changes energy is transferred
- closed systems are systems where neither matter nor energy can enter or leave
- the net change in the total energy of a closed system is always 0
- energy transfer
- when energy is transferred to an object the energy is stored in one of the objects energy stores
- energy is transferred mechanically (by a force doing work), electrically (work done by moving charges), by heating, or by radiation
- heat transfer
- example: kettle
- work done
- another way of saying energy transferred
- work can be done when current flows or by a force moving an object
- energy stores
- specific heat capacity
- specific heat capacity is a scientific way of saying how hard it is to heat something up
- specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1oc
- more energy needs to be transferred to the thermal energy store of some materials to increase their temperature
- materials that need to gain lots of energy in their thermal energy stores to warm up also transfer lots of energy when they cool down again
- conservation of energy and power
- conservation of energy principle
- energy can be transferred usefully, stored or dissipated, but can never be created or destroyed
- when energy is transferred between stores, not all the energy is transferred usefully into the stores you want it to go to - some energy is always dissipated
- dissipated energy is sometimes called wasted energy because the energy is not being stored usefully
- in closed systems the energy transfers occur within the system, but no energy leaves the system - so the net change is zero
- power
- the rate of energy transfer or the rate of doing work
- power is measured in watts
- 1 watt = joule of energy transferred per second
- a powerful machine doesn't necessarily exert a strong force - it transfers a lot of energy in a short space of time
- conservation of energy principle
- reducing unwanted energy transfers and improving efficiency
- efficiency
- useful devices are only useful as they can transfer energy from one store to another
- the less energy wasted in the energy store the more efficient the device is
- you can improve the efficiency of energy transfers by insulating objects, lubricating them or making them more streamlined
- no device is 100% efficient and the wasted energy is usually transferred to the thermal energy store - except electric heaters as all the energy in the electrostatic energy store is transferred to the useful thermal energy store
- reducing unwanted energy transfers
- lubrication
- reduces frictional forces that occur when objects rub together
- whenever something moves, there's usually at least one frictional force acting against it - causing some energy to be dissipated
- usually liquids so they can flow easily between objects and coat them
- thermal insulation
- cavity walls - made up of inner and outer wall with an air gap in the middle - air gap reduces amount of energy transferred by conduction, filled with foam
- loft insulation - can reduce convection currents
- double-glazed windows - work in the same way as cavity walls
- draught excluders - around doors and windows to reduce energy transfers by convection
- heating
- when an object is heated, energy is transferred to the kinetic energy stores
- this causes the particles to vibrate more and collide with each other - during the collisions energy is transferred between the particles' kinetic energy stores - this is conduction
- thermal conductivity is a measure of how quickly energy is transferred through a material - materials with a high thermal activity transfer energy between the particles at a faster rate
- if the particles are free to move the particles moving faster means that the space between individual particles increase - causes the density of the region being heated to decrease
- because liquids and gases can flow the warmer and less dense the region will rise above denser, cooler regions - energetic particles move away from hotter and cooler regions - this is convection
- when an object is heated, energy is transferred to the kinetic energy stores
- lubrication
- efficiency
- energy stores and systems (object)
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