P7- Energy Flashcards
What is kinetic energy?
An object has it when it’s moving.
What is thermal energy?
The hotter an object is, the more thermal energy it has.
What is chemical energy?
Energy that is released by a chemical reaction.
What is gravitational potential energy?
Energy that an object has when it is in a gravitational field (eg. when it can fall)
What is elastic potential energy?
Energy that a stretchable object can have
What is electrostatic energy?
eg. two charges that can attract or repel
What is magnetic energy?
eg. two magnets that can attract or repel
What is nuclear energy?
Energy that is released by atomic nuclei in nuclear reactions
What are the four ways energy is transferred between stores?
Mechanically, electrically, by heating, by radiation
How is energy transferred mechanically?
An object moving due to a force eg. pushing, pulling, stretching or squashing
How is energy transferred electrically?
A charge through a voltage, eg. charges moving around a circuit
How is energy transferred by heating?
Energy transferred by a hotter object to a colder object, eg. heating a pan of water
How is energy transferred by radiation?
Energy transferred eg. by light/sound waves
What is the law of conservation of energy?
Energy can be stored, transferred between stores, and dissipated, but it can never be created or destroyed. The total energy of a closed system that has no net change.
What does “dissipate” mean?
The energy is spread out and lost.
What is the energy transfer when a ball rolls up a slope?
Energy is transferred mechanically from the kinetic energy store of the ball to its gravitational energy store
What is the energy transfer when a bat hits a ball?
Energy in the kinetic energy store of the bat is transferred to the thermal energy stores of the bat, the ball and their surroundings. Some energy is transferred mechanically from the KE store of the bat to the KE store of the ball.
The rest is carried away by sound.
What is the energy transfer when an electric kettle heats water?
Energy is transferred electrically from the mains to the thermal energy store of the kettle’s heating element. It is then transferred by heating to the thermal energy store of the water.
What happens to some of the input energy in a process?
Some is always lost or wasted, often to thermal energy stores by heating.
How can you calculate total energy input with useful energy output and wasted energy?
Total energy input = Useful energy output + Wasted energy
How can you calculate the efficiency of a device with useful output energy and input energy?
Efficiency (%) = Useful output energy transfer (J) ÷ Input energy transfer (J)
What are the free ways that energy can be transferred by heating?
Conduction, convection and radiation
What is conduction?
The process where vibrating particles pass extra energy in their kinetic energy stores to the kinetic energy stores of neighbouring particles.
What is thermal conductivity?
It describes how well an object transfers energy by conduction
In what does conduction usually occur in?
Solids
What is convection?
It occurs when the particles with more energy in their kinetic energy stores move from the hotter region to the cooler region - and take their kinetic energy stores with them.
In what does convection occur in?
Liquids nad gases
What happens when you heat a liquid?
The particles move faster, and the fluid expands, becoming less dense. The warmer, less dense fluid rises above its colder, denser surroundings.
As the warm fluid rises, the cooler fluid takes its place. The process continues until you have a circulation of fluid (convection currents).
How is transferring energy by radiation different to conduction or convection?
Conduction and convection require particles. On the other hand, radiation can travel through a vacuum.
What is a good absorber and emitter of radiation?
Matt black surfaces
What are bad absorbers and emitters of radiation?
Light coloured, smooth and shiny surfaces
How does loft insulation reduce energy loss?
Fiberglass “wool” laid on loft floors and ceilings reduces energy loss from the house by conduction and convection.
How does a hot tank water jacket reduce energy loss?
Reduces conduction, keeping the water hot.
How do cavity walls and cavity wall insulation reduce energy loss?
Two layers of bricks with a gap between them reduce conduction, but energy is also transferred across the gap by convection. Squirting insulating foam into the gap traps pockets of air to minimise convection.
How does double glazing reduce energy loss?
Two layers of glass with an air gap reduce conduction.
How do thick curtains reduce energy loss?
Reduces heat loss by convection and conduction through windows.
How does draught-proofing reduce energy loss?
Strips of foam and plastic around doors and windows stops hot air going out, reducing convection.
How can you reduce energy loss from hot water pipes?
Insulating the pipes to reduce conduction/radiation
Painting the pipes white to reduce energy loss by radiation
Making the pipes as short as possible
Making the pipes as wide as possible, so they have a smaller surface area:volume ratio, meaning that less water is near the surface of the pipe, and so less energy is lost by conduction.
How does the thickness of walls affect energy transfer
The thickness of walls affects how quickly energy is transferred out of a building. The thicker the walls, the lower the rate of energy transfer.
How does reducing friction reduce energy loss?
Friction in a system leads to energy being lost by heating. This can be reduced with lubrication or changing the shape of an object.
What is the relationship between the energy transferred to/from an object’s kinetic energy store and the energy transferred from/to the object’s gravitational potential energy store?
Energy transferred to/from an object’s kinetic energy store = Energy transferred from/to the object’s gravitational potential energy store
How do you calculate kinetic energy?
Kinetic energy (J) = 0.5 * mass * speed²
How do you calculate gravitational potential energy?
Gravitational potential energy = mass * height * gravitational field strength
What happens to the energy in an elastic object when it is squashed or stretched?
Kinetic energy is transferred from the object affecting the elastic object, into its elastic potential energy store.
How do you calculate the energy transferred when an object is squashed or stretched?
Energy transferred = 0.5 * Spring constant * Extension²
What happens when a stretched/squashed elastic object returns to its original form?
The energy in its elastic potential store transfers back to the object’s kinetic energy store.
How is some energy lost in electrical circuits?
Energy is lost through thermal energy stores of the wires through heating.
How can you calculate the energy transferred to an electrical device?
Energy transferred = Power * Time
How can you calculate power with current and voltage?
Power = Current * Voltage
What is power?
How much energy is transferred per second
