3. Conservation of Energy Flashcards
What is meant by the conservation of energy?
- The total amount of energy in a closed system remains constant.
- Energy cannot be made or destroyed but can change from one form to another.
What is a closed system?
No energy (or matter) is transferred in or out of the system, so there is no net change in total energy.
Describe the energy changes involved when an object is projected upwards / downwards?
KE transferred to GPE, then vice versa as it falls downwards.
Name the eight types of energy store
- Kinetic energy
- Gravitational potential energy (GPE)
- Elastic potential energy
- Electrostatic
- Thermal
- Chemical
- Magnetic
- Nuclear
Name the four types of energy transfer
- Mechanical (a force doing work)
- Electrical (work done by moving charges)
- Heating
- Radiation (e.g. light or sound)
State any changes in the total energy of a ball that is kicked, assuming that no external forces act.
The total energy of the system remains constant due to the conservation of energy.
Describe the energy changes that occur in a filament light-bulb.
- Electrical energy is transferred into light and heat energy.
- Light is a useful energy form, heat is waste energy.
Describe the energy transfers for a bungee jumper.
- When falling, the GPE is converted to KE of the jumper.
- As the cord tightens, KE is converted and stored as elastic potential energy (EPE).
- At lowest point, the jumper’s initial GPE equals the EPE stored in the cord.
Explain why a bungee jumper slows down once the cord begins to stretch.
- Kinetic energy decreases since it is converted to elastic potential energy.
- Since KE is proportional to (velocity)², as KE decreases, so does velocity.
What is waste energy?
The energy that is not used by the device for its desired purpose, or not converted into the desired form.
State the consequence for energy transfer of a material with a high thermal conductivity.
The rate of energy transfer through the material is higher than for a material with a lower thermal conductivity.
Do double-glazed windows have a higher or lower thermal conductivity than single-glazed windows?
Lower thermal conductivity, meaning less energy transfers through them.
State three methods of reducing heat loss in a building.
- Double glazing.
- Loft and wall insulation.
- Thicker walls.
How can you reduce unwanted energy transfer in a mechanical system?
Reduce friction by lubricating moving parts.
How can the efficiency of a system be increased?
- Reducing waste output (by lubrication, thermal insulation, etc.).
- Recycling waste output (e.g. recycling thermal waste energy as input energy).
Give an example of a thermal insulation material.
Cotton wool
What are renewable resources?
Energy sources which can be replenished as it is being used up.
Give four examples of renewable energy resources.
- Wind energy
- Hydro-electricity
- Tidal energy
- Solar energy
Give an example of a non-renewable energy resource.
Fossil fuels (for example coal, oil and gas)
What are the advantages of generating power using gas rather than coal?
- Flexible generation - gas power stations have short start-up times so can be switched on/off more readily.
- Lower emissions of carbon dioxide.
State two disadvantages of using renewable energy resources to generate power.
- Output often determined by external factors (like wind speed), so supply is uncertain.
- Renewable fuels often produce less energy per kg (so more expensive).
Explain the environmental impacts of burning fossil fuels.
- Carbon dioxide contributes to the greenhouse effect, and causes global warming.
- Sulfur dioxide leads to acid rain, which can damage buildings and crops.
State three advantages of fossil fuels as an energy resource.
1) Reliable - not dependent on external factors so can generate power anytime.
2) Produce large amounts of energy per kg.
3) Still relatively abundant, so cost-effective.
State three advantages of nuclear power.
1) Very large amounts of energy per kg of fuel.
2) No greenhouse gases released, so doesn’t contribute to climate change.
3) Low fuel costs.
State three disadvantages of nuclear power.
1) Produces nuclear waste which is harmful to humans and must be safely stored for centuries.
2) Non-renewable energy resource so it will run out.
3) Risk of nuclear accidents, which have fatal consequences on humans and the environment.
Give examples of social factors to consider in energy production.
- Visual pollution
- Sound pollution
(both of these are disadvantages of wind farms)
How does hydroelectric power (HEP) produce energy?
- Rainwater collects behind a dam.
- When this water is released, it is used to turn a turbine.
- This turbine turns a generator which produces electricity.
What are some disadvantages of using biofuels?
- When plants are burned/decay they release carbon dioxide.
- In order to grow biofuels, you need to destroy land:
- Habitat destruction
- Deforestation
- CO₂ released when plants are cleared (for example, if they are burned)
- Growing biofuels reduces the land available for food crops.
What are the advantages of tidal energy sources?
- No greenhouse gas emissions.
- Fairly reliable (tides occur twice a day).
- Cheap to run as tides are natural, so cost-free.
What are the disadvantages of hydroelectric power?
- The dam may cause flooding.
- It can cost a lot to install the required infrastructure.
What are some advantages of solar panels?
- They don’t cause harm to the environment.
- They are a renewable resource (will never run out).
- They can be used in remote areas where other types of energy are less accessible.
Did electricity use increase or decrease between 1900 and 2000? Why?
Electricity use increased because:
- Population grew.
- People began to use electricity for more things.
Is electricity use increasing or decreasing from 2000 onwards? Why?
Electricity use decreasing because:
- Appliances are more efficient.
- People are more careful with amount of energy use.
What are three reasons as to why we’re increasing use of renewable energy resources?
1) Burning fossil fuels is very damaging to environment.
2) We need to learn how to get by without non-renewable resources before they run out.
3) Pressure on governments and companies has led them to introduce renewable energy targets.
Describe the energy changes involved when an object is projected up a slope.
KE transferred to GPE (and also to heat if friction is present)
Describe the energy changes involved when a moving object is hitting an obstacle.
KE transferred to sound / KE transferred to obstacle if that moves too
Describe the energy changes involved when an object is being accelerated by a constant force.
- Object is having work done to it, with it gaining KE.
- Whatever supplies the force is having its energy transferred to KE.
Describe the energy changes involved when a vehicle is slowing down.
KE is transferred to heat (through brakes)
Describe the energy changes involved when boiling water in a kettle.
Energy transferred electrically from the mains to the thermal energy store of kettle’s heating element. Then energy is transferred by heating to thermal energy store of water.
