Topic 3 - Conservation Of Energy Flashcards
What does conservation of energy mean?
Energy is never created or destroyed. It can be stored, transferred between stores and dissipated but never created or destroyed.
How can energy be transferred between stores mechanically?
A force acting on an object and doing work eg pushing
How can energy be transferred between stores electrically?
A charge doing work eg charges moving around a circuit
How can energy be transferred between stores by heating?
Energy transferred from a hotel object to a colder object eg heating pan on hob
How can energy be transferred between stores by radiation?
Energy transferred by waves eg energy from the sun reaching earth by light.
Explain what happens in the energy transfer of a ball rolling up a slope
Ball does work against the gravitational force so energy is transferred mechanically from ball kinetic energy store to its GPE store
Explain what happens in the energy transfer of a bat hitting a ball
Bat has energy in its KE store. Some is transferred mechanically to the ball’s KE store. Some energy transferred mechanically to the thermal energy stores of bat + ball. Rest carried away by sound.
Explain what happens in the energy transfer of a rock dropped from a cliff
Assuming no air resistance, gravity does work on rock so rock constantly accelerates towards ground. Energy is transferred mechanically from rocks GPE store to its KE store.
Explain what happens in the energy transfer of a car slowing down without breaking
Energy in KE store of car is transferred mechanically (due to friction) and then by heating to the thermal energy stores of car and road
Explain what happens in the energy transfer of a kettle boiling water
Energy transferred electrically from mains to heating element of kettle + then by heating to thermal energy store of water.
What is the equation for kinetic energy?
KE (J) = 0.5 x m(kg) x v2(m/s)
What is a closed system?
A system (collection of objects) that can be treated completely on its own without any energy being exchanged to or from the surroundings.
What happens in a closed system?
When there are energy transfers in a closed system there is no net change to the total energy in that system.
When are energy transfers useful?
Energy is only useful when it’s transferred from one store to a useful store.
Explain how mechanical processes become wasteful
They become wasteful when they cause a rise in temperature so dissipating energy in heating the surroundings
How does lubrication reduce unwanted energy transfers?
For objects touching each other lubricants are used to reduce the friction between the objects’ surfaces when they move. Eg oil.
How does insulation reduce unwanted energy transfers?
Thicker walls, cavity walls and insulation decreases the rate of energy transfer through them and reduces the amount of energy transferred by conduction.
Are devices 100% efficient? (Eg electric motor)
No device is 100% efficient. Eg 100J supplied to motor, 80J of energy transferred is useful and 20J energy wasted from thermal
What are the effects of having lower thermal conductivity walls?
The slower the rate of energy transfer through them meaning the building will cool slower
What are the effects of a building having thicker walls?
The thicker the wall the slower the rate of energy transfer so building will cool down slower
What is the equation for efficiency?
Efficiency=useful energy transferred(J)/
Total energy supplied to device (J)
How can efficiency be increased?
Lubrication and thermal insulation
What are the main energy sources available for use on earth?
Bio fuels Wind Solar Hydro electricity Fossil fuels Nuclear fuel Tides
What are fossil fuels?
Coal, oil, gas. Non renewable energy. Natural resources that form underground over millions of years and are burnt to provide energy.
Advantages of non renewable energy
Eg fossil fuels and nuclear energy. They can respond quickly to changes in energy demand. Cost to extract fossil fuels is low.
Disadvantages of non renewable energy
Produce lots of CO2 which contributes to global warming. Burning coal and oil releases sulfur dioxide which causes acid rain. Oil spillages affect animals that live in and around the sea.
