P1-conservation and dissipation of energy Flashcards
What are the eight energy stores?
Thermal energy store Kinetic energy store Gravitational potential energy store Elastic potential energy store Chemical energy store Magnetic energy store Electrostatic energy store Nuclear energy store
What are the different ways energy can be transferred?
- Mechanically(by a force doing a work)
- Electrically(work done by moving charges)
- Heating
- Radiation(e.g light or sound)
What is a system?
A system is a single object or a group of objects that you are interested in
What happens when a system changes?
When a system changes, energy is transferred. It can be into or away from the system, between different objects in the system or between different types of energy stores(e.g from the kinetic store of an object to its thermal energy store)
What is a closed system?
A closed system are systems where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero.
How is energy transferred be heating e.g from boiling water in a kettle?
Think of the water as the system. Energy is transferred to the water by heating, into the water’s thermal energy store causing the temperature of the water to rise.
What energy stores does it go through when an object falls and hits the ground.
First it has a lot of gravitational potential energy but as the object is falling it speeds up which transfers the energy into the kinetic energy store and when it hits the ground the energy is transferred to the surroundings.
What are chemical energy stores?
Fuels, foods or the chemicals found in batteries. The energy is transferred during chemical reactions.
What is kinetic energy store?
Kinetic energy stores describe the energy an object has because it is moving.
What is gravitational energy store?
Gravitational potential energy stores are used to describe the energy stored in an object because of its position, such as an object above the ground.
What is elastic potential energy store?
Elastic potential energy store describes the energy stored in a springy subject when you stretch it or squash it.
What is thermal energy store?
Thermal energy store describes the energy a substance has because of its temperature.
What is conservation of energy principle?
Energy can be transferred usefully, stored or dissipated but can never be created or destroyed.
When energy is transferred is all of it used in a useful way?
No, not all the energy is transferred usefully into the store that you want it to go in. Some energy is always dissipated when an energy transfer takes place.
What is dissipated energy?
It is wasted energy because the energy is being stored in a way that is not useful.
What is work done?
The energy transferred when a force acts over a distance
What does it mean work is done on an object?
Work is done on an object when a force makes the object move
What unit is work done measured in?
Joules
What is the equation of work done?
Work done(joules)=force(newtons) times distance(metres) W=Fs
Kinetic store info, just read it, its okay :)
Anything that is moving has energy in its kinetic energy store. Energy is transferred to this store when an object speeds up and is transferred away from this store when an object slows down.
The energy in the kinetic energy store depends on the objects mass and speed. The greater the mass and the faster it is going, the more energy there will be in its kinetic energy store.
What is the equation for kinetic energy?
Kinetic energy(joules)=1/2 mass(kg) times speed^(m/s) kinetic energy=1/2mv^
Gravitational potential energy store info, just read it, its okay :)
Lifting an object in a graviational filed requires energy. This causes a transfer of energy to the gravitational potential energy(gpe) store of the raised object.
The higher the object is lifted, the more energy is transferred to this store.
The amount of energy in a graviational potential energy store depends on the objects mass, its height and the strength of the gravitational field the object is in.
What is the equation to find gravitational potential energy?
gravitational potential energy(joules)=mass(kg) times gravitational field strength(N/kg) times height(metres)
gravitational potential energy=mgh
How can energy be transferred into the elastic potential energy store?
Stretching or squashing an object
What is the equation to work out elastic potential energy?
Elastic potential energy(joules)=1/2 spring constant(N/m) times extension^(m)
elastic potential energy=1/2ke^
Why are useful devices useful?
Because they can transfer energy from one store to another
What is input energy?
The energy supplied to a device
How do you work out efficiency?
efficiency=useful output energy transferred/ total input energy
you can give it as percentage by timising it by 100 if you want
Can a device by 100 efficient?
No, no device can be 100% efficient except electric heaters because all the energy in the electrostatic energy store is transferred to ‘useful’ thermal energy stores.
Reasons why devices waste energy (friction) and how to reduce the problem
Friction between the moving parts causes heating
Lubricate the moving parts to reduce friction
Reasons why devices waste energy(wires) and how to reduce the problem
The resistance of a wire causes the wire to get hot when a current passes through it
In circuits, use wires with as little electrical resistance as possible
Reasons why devices waster energy(air resistance) and how to reduce the problem
Air resistance causes a force on a moving object that opposes its motion. Energy transferred from the object to the surroundings by this force is wasted
Streamline the shapes of moving objects to reduce sir resistance.
Reasons why devices waste energy(sound) and how to reduce the problem
Sound created by machinery causes energy transfer to the surroundings
Cut out noise(e.g tighten loose parts to reduce vibrations)
What is the useful energy and energy wasted in a light bulb?
Light emitted from the glowing filament
Energy transfer from the filament heating the surrounding
What is the useful and wasted energy in a electric heater?
Energy heating the surroundings
Light emitted from the glowing element
What is the useful and wasted energy in a electric toaster?
Energy heating bread
Energy heating the toaster case and the air around it
What is the useful and wasted energy in a electric kettle?
Energy heating water
Energy heating the kettle itself
What is the useful and wasted energy in a hair dryer?
Kinetic energy of the air driven by the fan. Energy heating air flowing past the heater filament
Sound of fan motor and energy heating the hair dryer itself
What is the useful and wasted energy in a electric motor?
Kinetic energy of objects driven by the motor. Gravitational potential energy of objects lifted by the motor
Energy heating the motor and energy transferred by the sound waves generated by the motor.
What is power?
The rate of energy transfer
What is power measured in?
Watts
1 watt = 1 joule of energy transfer per second
What is the equation to work out power?
Power(watts)=energy transferred(joules)/time(seconds)
How do you work out efficiency for power?
efficincy= useful power out/total power in times 100
How do you work out wasted power?
power wasted= total power in- useful power out
