Energy Flashcards
8 stores of energy?
- Kinetic
- Thermal
- Chemical
- Nuclear
- Elastic Potential energy
- Gravitational Potential Energy
- Magnetic
- Electrostatic
Energy must be transferred to do what?
Work
What are the 4 ways to transfer energy?
- Radiation
- Electrically
- Mechanically
- Heat
Where does the earths energy come from?
The sun - transferred by radiation
Definition of transfer by radiation?
When energy is transferred as sound, light (not touching anything) - not electrically, mechanically or by heating :)
Definition of energy transferring electrically?
When energy is transferred through currents
Definition of transfer by heating?
When energy is transferred as objects heat up
Definition of mechanical transfers of energy?
When energy is transferred by parts moving
Law of Conservation of energy?
Energy cannot be created or destroyed, only transferred from one type to another
What is energy measured in?
Joules
What is work?
Energy transferred
equation for work done =
work done (J) = force (N) * distance (m)
Weight =
weight (N) = mass (Kg) * gravity (9.8 n/kg)
GPE =
GPE (J) = (mass (Kg) * gravity(9.8 n/kg) - weight) * height (m)
KE =
KE (J) = 0.5 * M (Kg) * (v*v) (m/s)
EPE =
EPE (J) = 0.5 * k (N/M) * (x*x) (M)
What happens when a system changes?
Energy is transferred
What is a system?
A single object or group of objects of interest
What is a closed system?
A system in which neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero.
Work can be done when (2) ?
- Current flows
2. Force moves an object
What is kinetic energy?
How can you increase the KE of an object?
When is KE transferred to and away from an object?
Anything that moves has kinetic energy
Increasing an objects mass or speed increases KE
When an object speeds up, KE is transferred to this store, when an object slows down, KE is transferred away
What is GPE?
How can you increase the GPE of an object?
When is GPE transferred to and away from an object?
GPE is energy an object has based on its position above the earths surface
Increasing the objects mass, height, or the strength of the gravitational field the object is in increases its GPE
The higher an object is lifted, the more energy is transferred to the store, the more the object is lowered, the more GPE transfers away from the store
What is EPE?
How can you increase the EPE of an object?
Elastic potential energy is energy stored as a result of applying a force to deform (stretch/squash) an elastic object
EPE is dependant on the length the object is stretched and the spring constant
What does efficiency tell us?
It tells us how much of the energy put in is transferred usefully
Efficiency =
efficiency(%) = useful energy output/total energy input* 100
note - efficiency equation can be done in terms of power
useful power output (W) / total power output (W)
* 100
What is Power?
Power is how much work is done per second - measure in Watts
Power =
Power (W) = work (J) / time (S)
1 W =
1 J per second
What is useful energy?
Energy transferred to where it is wanted in the way it is wanted
What is wasted energy?
Energy that is not usefully transferred
Energy that is not transferred usefully is…
dissipated
Why do devices waste energy? (4)
- Friction between moving parts causes heating
- The resistance of a wise causes the wire to get hot when current passes through it
- Air resistance causes a force on a moving object that opposes its motion
- Sound created by machinery causes energy transfer to the surroundings
How to reduce wastes of energy (4)?
- Lubricate moving parts to avoid friction
- Uses wires in circuits with as little electrical resistance as possible
- Streamline objects to reduce air resistance
- Cut out noise by tightening loose parts for example
energy changes when an is object projected upwards
Energy of the object starts of by being stored as kinetic energy, it slows down as it increases in height because the KE is transferred to GPE
energy changes when an moving object hits an obstacle
energy shifts from kinetic store of object to the thermal energy store of object and obstacle
energy changes when an object accelerates at a constant force
energy shifts from chemical store of the fuel to the kinetic store of the object
energy changes when a object slows down
energy shifts from the kinetic store of the vehicle to the thermal store of the brakes and surroundings
energy changes when bringing water to boil in an electric kettle
energy shifts from chemical store (in the electricity) to the thermal store of the water
Light bulb useful energy and wasted energy?
useful: light emitted from the glowing filament
wasted: energy transferred from the filmet heating the surroundings
Electric heater useful energy and wasted energy?
useful: Energy heating surroundings
wasted: Nothing really (some light emitted from glowing element)
Electric toaster useful energy and wasted energy?
useful: energy heating bread
wasted: energy heating the toaster case and surrounding air
Electric kettle useful energy and wasted energy?
useful: Energy heating water
wasted: Energy heating kettle itself
Hairdryer useful energy and wasted energy?
useful: kinetic energy of air driven by fan and energy heating air flowing past heating element
wasted: Sound of fan motor energy heating hairdryer itself
Electric motor useful energy and wasted energy?
useful: kinetic energy of objects driven by motor, GPE potential energy of object lifted by motor
wasted: energy heating the motor and energy transferred as sound
What is the spring constant? What is extension?
The spring constant, k, is a measure of the stiffness of the spring - the higher the k, the stiffer the spring
The increased length of an object when stretched is the extension, it is equal to:
new length - original length
What is the limit of proportionaltiy?
The limit of proportionality refers to the point beyond which Hooke’s law is no longer true when stretching a material. The elastic limit of a material is the furthest point it can be stretched or deformed while being able to return to its previous shape. Once a material has gone past its elastic limit, its deformation is said to be inelastic.
