Conservation of Energy Flashcards
Different energy stores and their meaning
Thermal - any object - the hotter it is, the more energy it has in this store
Kinetic - anything moving has energy I this store
GPE - anything in a gravitational field
Elastic potential - anything stretched
Magnetic - two magnets that attract and repel each other
Electrostatic - two charges that attract and repel each other
Nuclear - atomic nuclei release energy in nuclear reactions
Kinetic energy
-Movement means energy in an object’s kinetic energy store
-Energy transferred when an object speeds up and is transferred away from this store when an object slows down.
-Energy in kinetic store depends on objects mass and speed
Kinetic energy formula
Kinetic energy (J) = 1/2 x mass (m) x speed2 (m/s2)
Gravitational Potential Energy
- Raised objects store energy in GPE stores
- Lifting an object in gravitational field transfers energy into gpe store
-The higher the object is lifted, the more energy is transferred in.
-Amount of energy depends on object’s mass, height and strength of gravitational field.
Gravitational Potential Energy formula
Change in GPE = Mass (kg) x Gravitational field strength (N/kg) x change in vertical height (m) or
ΔGPE = m x g x Δh
Principle of Conservation of energy
Energy can be stored, transferred between stores, and dissipated, but it can never be created or destroyed
What is a Closed system?
- A closed system is a collection of objects that can be treated completely on its own.
-The total energy of a closed system has no net change - If a question asks you where the energy of a system increases or decreases it is not a closed system
-Can turn something into a closed system by increasing the number of things part of it.
Different types of energy transfer
Mechanically - a force acting on an object and doing work (e.g pushing, stretching squashing)
Electrically - a charge doing work (e.g charges moving round a circuit)
By heating - energy transferred from a hotter object to a colder object
By radiation - energy transferred by waves
Examples of energy transfers - bat hitting ball
Bat has energy in kinetic energy store. Some transferred mechanically to the ball, some transferred mechanically to thermal energy stores of bat and ball. The rest is carried away by sound by radiation
Examples of energy transfers - a rock dropped from a cliff
- gravity does work on the rock meaning rock acceelerates towards the ground
- energy is transferred mechanically from the rock’s GPE store to its kinetic energy store.
Examples of energy transfers - A car slowing down (without braking)
- Energy from kinetic energy store of car is transferred mechanically due to friction between the tyres and the road.
- then by heating to the thermal energy stores of the car and the road
Examples of energy transfers - kettle boiling water
- energy transferred electrically from the socket to the heating pad of kettle
- then by heating to the thermal energy stores of the water.
Principle of useful energy
- Energy is only useful when it is transferred from one store to a useful store
total energy input = useful energy output + wasted energy
Mechanically wasted energy
-Whenever work is done mechanically, frictional forces have to be overcome (e.g moving parts rubbing together and air resistance)
-The energy needed to overcome these forces is transferred into the thermal energy stores of the object and surroundings
-This energy is not useful
How to calculate efficiency
efficiency = useful energy transferred by device / total energy supplied by device
Using diagrams to show efficiency
-No device is 100% efficient
-Sankey diagrams are used to show when some are more efficient than others
-The thickness of the arrows represents how much energy is being transferred.
-Wasted energy splits off vertically downwards
Ways of reducing energy transferred wasted energy - lubrication
For a objects that are touching with a frictional force, lubricants can be used to reduce the amount of thermal energy transferred mechanically into the objects thermal energy store
- this is because it can flow easily between objects and coat them.
Ways of reducing energy transferred wasted energy - Insulation
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Process of conduction
- When one side of an object, the particles in the hotter part vibrate more and collide with each other
- This transfers energy from their kinetic energy stores to other particles which then vibrate faster and so on
Thermal conductivity
-Describes how well a material transfers energy by conduction
-Metals have high thermal conductivity and gases have low thermal conductivity
Ways of reducing energy transferred wasted energy - Insulation
- To reduce a buildings ‘rate of cooling’, walls should be thick and have a low thermal conductivity
- Houses have cavity walls and double-glazed windows with an inner and outer wall with an air gap in the middle, reducing amount of energy transferred through walls by conduction.
Non - renewable energy sources
-Include coal, oil and natural gas
-Fossil fuels which are burnt to provide energy
-They are finite and will run out one day
-They are very reliable
Renewable energy sources
-Include solar, wind, hydro-electricity, Bio fuel and tides
-These will never run out
-Most do damage to the environment but in less nasty ways than non renewables
-Don’t produce as much energy and are unreliable as they depend on the weather
Solar Cells
-Often used in remote places (e.g to power road signs and satellites)
-There is no pollution except when making it
- Initial costs are high but there are little to no running costs
-Best in sunny countries but can be used in cloudy countries
-Can’t produce at night and cannot increase production if there is extra demand
