P1: Conservation And Dissipation Flashcards
What is energy?
Energy is the ability to do work
What are all energy stores?
- Chemical
- Kinetic
- Gravitational Potential
- Thermal
- Elastic Potential
- Magnetic
- Electrostatic
- Nuclear
What is chemical energy and examples?
The energy stored in chemical bonds between molecules
Food, cells, fuel, muscles
What is kinetic energy and examples?
The energy of moving object
Runners, buses, particles colliding
What is Gravitational Potential energy and examples?
The energy of an object at height
Aeroplanes, Mugs on a table, Skydivers
What is Thermal energy and examples?
Thermal energy refers to the energy contained within a system that is responsible for its temperature.
Hot coffee, sun
What is Elastic Potential energy and examples?
Energy stored when an object is compressed or stretched
Elastic band, spring
What is magnetic energy and examples?
Energy stored when repelling charges have been moved closer
Fridge magnets, compasses
What is electrostatic energy and examples?
The energy stored when opposite charges have been moved closer
Van de Graaff Generator
What is nuclear energy and examples?
The energy stored in the nucleus of an atom
Nuclear reactor
What are all energy transfers?
Heat
Electrical
Radiation/ waves (sound and light)
Mechanical
What energy transfers occurs with a car brake when it stops a car
The car’s kinetic energy is transferred mechanically to the tires’ thermal stores, while transferring energy as sound waves.
Explain what happens as the pendulum moves past the middle position?
As the pendulum reaches the middle position, the gravitational potential is at a minimum, whilst kinetic energy reaches its maximum. As the maximum height is reached, gravitational potential increases and the kinetic energy decreases
What happens to a swinging pendulum when there is air resistance?
A pendulum affected by air resistance will not return to the height it was originally released at as additional energy is required to the frictional force and it will eventually stop. As the energy is transferred between gravitational potential and kinetic energy, the energy is partially transferred to thermal energy or is dissipated, gradually causing the pendulum to slow down and stop.
What is conservation of energy?
Energy cannot be created or destroyed, it can only be transferred from one store to another
What is a closed system?
A closed system is an isolated system in which no energy transfers take place into or out of the system
Why does a ball not return to the height is was dropped from?
The bouncy ball will not return to the height it was originally dropped at due to it being affected by air resistance and as energy is transferred through mechanical transfer between gravitational potential and kinetic energy, some energy is dissipated into the surroundings through thermal and sound energy. As a result, the ball eventually slows down until it stops.
What is work?
Work is the amount of energy transferred (changed) when a force moves (in the direction of the force)
How is work calculated?
Work (J) = Force (N) x Distance (m)
What is lifting force equal to?
The weight of the object
What is friction?
Friction is an opposing force to direction of movement when two surfaces are in contact
Why do brake pads on cars get hot?
Friction between the brakes pads and the wheel discs opposes rhe motion of the wheel, the force of friction does work on the brake pads and discs.
When the brakes are applied to stop the wheel the kinetic energy store transfers energy to the thermal energy store of the brake pads and discs. These become hot and transfer energy by heating to the surroundings.
Explain the changes in energy stores a meteorite enters the Earth’s atmosphere
Gravitational potential: The meteorite initially has high gravitational potential energy due to its position inn the earth’s gravitational field
Kinetic energy: As the meteorite accelerates due to gravity, its gravitational potential enrrgy decreases as it is converted imto kinetic energy.
What are the steps to investigate work done?
1.Lay the metre ruler on the bench.
2. Attach the Newtonmeter to the block.
3. Pull the block along the bench for one metre and record the force it took on the Newtonmeter.
4. Repeat 2 more times
5. Repeat whole investigate with rubber bands around the block.
What is another equation for work done (often for gravitational potential)?
Weight(N) x Height (m)
What is the equation for measuring change in gravitational potential energy?
Mass(kg) x gravitational force (N/kg or m/s^2) x height (m)
What is kinetic energy?
The energy an object has because of its motion depends on its mass and velocity.
How is kinetic energy calculated?
1/2 x mass x velocity^2
How is elastic potential energy calculated?
1/2 x Spring constant (N/m) x extension(m) ^2
What is Hooke’s Law?
Hooke’s Law states that if you double the force then the extension will double
What is useful energy?
Energy transferred to where it is wanted and in the form it is wanted
What is wasted energy?
Wasted energy is energy that is not usefully transferred
What happens to wasted energy?
Wasted energy is eventually transferred to the surroundings, which become warmer. This dissipated energy is too spread out to do useful work and so cannot be reused. This is why it is important to reduce the amount of energy that is wasted.
What is a sankey diagram?
A diagram used to represent the energy input and the useful and wasted energy outputs.
One large arrow (useful/wasted depending on which is larger), one smaller arrow coming off
What does it mean to be efficient?
When there is a higher useful energy product than wasted energy output
How is energy efficiency calculated?
Useful energy output/ Total input energy
What is efficiency limit?
No device can be more than 100% efficient because you cannot create energy.
You cannot get more energy out of a machine you put into it
How may energy efficiency be increased in an engine?
Lubricate moving parts to reduce friction
Tighten loose parts to reduce excess movement and noise
How may energy efficiency be increased in a power cable?
Use short and or thicker wires to reduce electrical resistance
How does a clockwork radio work?
- Turn the handle
- A clockwork spring winds up
- This increases the elastic potential energy of the spring as the extension is increased
- The spring unwinds,energy from its elastic potential store is transferred to its kinetic store
- A small electric generator them turns
-Electricity is generated
What is power?
Power (in physics) means the rate at which energy is transferred.
It is measured in Watts, W.
How is power calculated?
Energy (J)/ Time (S)
How is power wasted calculated?
Total power input - Useful power output
