combined science

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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
        • 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
    • 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
    • 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


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