Energy Flashcards
Name the energy stores:
- -Thermal energy stores -
- Kinetic energy stores -
- Gravitational energy stores -
- Elastic potential energy stores -
- Chemical energy stores -
- Magnetic (spectrum) energy stores -
- Electrostatic energy stores -
- Nuclear energy stores
What are the four ways in which energy is transferred?
- -Mechanically (force doing work)
- -Electrically (work done by moving charges)
- -Heating
- Radiation (waves)
What is a system?
a collection of particles
What happens when a system changes?
- Energy is transferred.
- It is transferred into or away from the system, between different objects in the system or between different types of energy stores.
What are closed systems?
- Closed systems are systems where neither matter nor energy can enter or leave it.
- The net change in the total energy of a closed system is always zero.
How is energy transferred in a kettle?
- electrically to the thermal energy store of the kettle’s heating element which then transfers by heating to the water’s thermal energy store.
What does work done mean?
Energy transferred
How can work be done?
Work can be done when current flows (energy is transferred against resistance in a circuit) or by a force moving an object.
What type of energy is stored for anything that is moving?
Kinetic
How is energy transferred to and from the kinetic energy store?
It is transferred to the kinetic energy store when an object gains speed and is transferred away from this store when an object slows down.
What increases the amount of energy in the kinetic energy store?
The larger the mass and the faster the speed of the object
What is the equation for calculating kinetic energy?
- Kinetic energy (j) = 1/2 x Mass(kg) x (speed x speed)(m/s)
- KE = 0.5 x mv^2
What energy do raised objects store?
gravitational potential energy
What does the amount of energy transferred to the gravitational potential energy store depend on?
- It depends on the object’s mass, height and the strength of the gravitational field the object is in.
- The higher the object is lifted, the more energy that is transferred
What is the equation for finding the change in energy of an object’s gravitational potential energy (GPE) stores for a change in height?
- G.P.E (J) = Mass(kg) x Height(m) x gravitational field strength (N/kg) G.P.E = mgh
What energy transfer do falling objects undergo?
Energy from the object’s gravitational potential energy store is transferred to its kinetic energy store
What is the relationship between the amount of energy in the G.P.E store and the kinetic energy store for a falling object with no air resistance?
Energy lost from the G.P.E store = Energy gained in the kinetic energy store
What effect does air resistance have on the energy transfer of a falling object?
It causes some energy to also be transferred to other energy stores
What effects can squashing and stretching have on the transfer of energy?
can transfer energy to its elastic potential energy store
What is the equation for working out energy in the elastic potential energy store so long as the limit of proportionality has not been exceeded?
- Elastic potential energy(J) =
- 0.5 x spring constant (N/m) x extension^2 (m)
- EPE = 0.5 x k x e^2 or EPE = 0.5 x F x e
Why do different materials have different specific heat capacities?
Because more energy needs to be transferred to the thermal energy stores of some materials to increase their temperature than others.
What happens in materials that need to gain lots of energy in their thermal energy stores to warm up?
These types of materials also transfer loads of energy when they cool down again. They can “store” a lot of energy.
What is specific heat capacity?
The amount of energy needed to
raise the temperature of 1kg of a substance by 1 degree Celsius
What is the formula with specific heat capacity?
energy transferred by heating(J) = Mass(kg) x specific heat capacity (J/kg degrees. Celsius ) x temperature change E = mcΔØ
What is the law of the conservation of energy?
Energy can be transferred usefully, stored or dissipated, but it can never be created or destroyed.
What is dissipated energy?
- Dissipated energy is the energy that is not usefully transferred into the store that you want it to go.
- It is sometimes called “wasted energy”
- No system is perfect.
- e.g. electrical cables warming up behind a TV is not useful as theram heat is conducted and lost
How does energy transfer wastefully in a closed system?
Energy transfers occur within the system to “waste” stores but no energy has left the system so the net change in energy is zero
What is power?
Power is the rate of energy transfer.
What is power measured in?
Power is measured in Watts.
One watt = 1 joule of energy transferred per second
What are the equations for calculating power?
- Power(W) = Energy transferred (J) /Time taken (s) P = E/t
- Power(W) = Work done(J) / Time (s) W = J/s
What is a powerful machine?
A powerful machine is one which transfers a lot of energy in a short space of time
Where does energy transferred to an object by heating go?
- It goes to the thermal energy store of an object.
- The energy is shared across the kinetic energy stores of the particles in the object.
What is conduction?
- the particles in the part of the object that is being heated gain energy and vibrate faster.
- The particles collide and this causes energy to be transferred between particle’s kinetic energy stores
What is thermal conductivity?
- Thermal Conductivity is a measure of how quickly heat energy is transferred through a material using conduction.
- Materials with high thermal conductivity transfer energy between particles quickly (higher rate of energy transfer).
- best thermal conductors: e.g. copper (and other metals) - when heated thermal heat energy travels quickly down the copper rod by thermal conduction
- poor thermal conductors (insulators) e.g. NON-METALS like wool, fibre glass
What is convection?
- Convection is where energetic particles in a liquid or gas move away from hotter to cooler regions.
- When a region of a liquid or gas is heated , the particles move faster and the space between the particles increases (less dense).
- The warmer and less dense region will rise above the denser and cooler regions)
How is energy transferred between a radiator and nearby air particles?
The air particles collide with the radiator and energy is transferred through conduction
What is a frictional force?
- A frictional force is a force that goes against something when its moving.
- This causes energy in the system to be dissipated.
How can friction be reduced between two objects?
Using lubricants
How can you prevent energy loss through heating in a house/building?
- -By having thick walls with low thermal conductivity (this slows rate of energy transfer) -
- Using thermal insulation
What are some thermal insulation methods?
- -Loft Insulation
- -Cavity Walls
- -Double-Glazed Windows
- -Draught excluders
How do cavity walls and double-glazed windows work?
- They both have an inner and outer layer (ie. wall or window) with an air gap in between.
- This reduces the amount of energy transferred by conduction through the windows or walls.
- Foam can be put in the cavity wall air gap to also reduce energy transfer by conduction
What does loft insulation do?
Loft insulation reduces convection currents being created in lofts
What do draught excluders do?
They are put around doors and windows to reduce energy transfer by conduction
What is waste (dissipation) energy?
The input energy that is transferred to a useless energy store