Energy Flashcards
What is the rule of conservation of energy?
Total energy before a process = Total energy after a process
What is the unit of energy?
Energy is measured in joules (J)
What the main energy stores?
- kinetic store
- gravitational potential store
- chemical store
- elastic store
- thermal store
How can we tell if there is a change to the kinetic store?
If the object changes speed
How can we tell if there is a change to the gravitational potential store?
If the object ends up higher or lower than it started out
how can we tell if there is a change to the chemical store?
If a chemical reaction takes place e.g. fuel burns, so you have less fuel than when you started
How to tell if there is a change in the elastic store?
If an object changes its shape
How can we tell if there is a change in the thermal store?
If the temperature of the object changes
What are the main energy pathways?
- Mechanical working
- electrical working
- heating by particles
- heating by waves
- light
- sound
- electromagnetic radiation
What is the mechanical working pathway?
Energy transferred by a force of physical mechanism (e.g. a pulley)
What is the electrical working pathway?
Energy transferred by an electric current
What is the heating by particles pathway?
Energy transferred from a higher temperature region to a lower temperature by moving particles (conduction, convection)
What is the heating by waves pathway?
Energy transferred from a higher temperature region to a lower temperature region by the emission of infrared radiation
What is the light pathway?
Energy transferred as visible light
What is the sound pathway?
Energy transferred as a sound wave
What is the electromagnetic radiation pathway?
Energy transferred as an electromagnetic wave (radio, microwave, infrared, visible, ultraviolet, X ray, gamma)
What is the equation for work done?
Work done by a force (joules- J) = force (N) x distance moved in the direction of the force (m)
W=Fs
What is work done?
If a force acts on an object, and the object moves in the direction of the force, we say that work has been done by the force
Finish the sentence: When work is done by a force, ________
Energy is transferred between stores
What is the equation for gravitational potential energy?
Change in the gravitational potential energy store (J) = mass (in kg) x gravitational field strength (N/kg) x height (m)
GPE = mgh
What are the units for power?
Watts
What is the equation for power?
power (in watts) x time (in seconds) = energy transferred (in joules)/work done (in joules)
P x t = E
What is the definition of power?
Rate of energy transfer
Rate at which work is done
equation for efficiency
efficiency = (useful energy transferred / total energy input ) x 100
OR
efficiency = (useful power output/total power input) x 100
What does it mean if energy is dissipated?
stored in a less useful way
What causes non-useful energy transfer and how can this be reduced for each one?
friction / air resistance (makes things heat up)
- use lubricants e.g. oil to reduce friction
- streamline your object
heating of surroundings (hot object in cooler surroundings)
- put on a lid
- use insulating materials
electrical resistance of wires (heat up when a current flows)
- use lower resistance cables
What factors affect the rate of energy transfer across the material?
a) the thickness
the greater the thickness, the smaller the rate of energy transfer across the barrier
b) the temperature difference
The greater the temperature difference, the greater the rate of energy transfer
c) the material itself
Materials with a high thermal conductivity transfer energy at a greater rate
Materials with a lower thermal conductivity transfer energy at a smaller rate
What environmental impact is there from using coal?
Releases carbon dioxide (greenhouse gas), can produce sulfur dioxide which causes acid rain, produces soot when burned
What are the different ways in which energy can be transferred?
Mechanical work, electrical work, heating by particles, heating by waves
What equation links kinetic energy, mass, and speed?
Kinetic energy = 0.5 x mass x (speed)^2
KE = 1/2 mv^2
Give five examples of a reliable energy resource
Coal, oil, gas, uranium, hydroelectric, biofuel, geothermal
Define the term “power”
Power is the rate of energy transfer
Give an example of a non-useful energy transfer
e.g. transfer to the thermal store of the surroundings
What are the different ways in which energy can be stored in a system?
Kinetic store, gravitational potential store, elastic store, thermal store, chemical store
Define the specific heat capacity of a material
The amount of energy needed to raise the temperature of 1 kg of an object by 1 degrees Celsius
Give five examples of a renewable energy resource
e.g. wind, solar, tidal, hydroelectric, bio-fuel, geothermal, waves
What are the effects of thermal conductivity of the walls of a building on the rate of cooling?
The greater the thermal conductivity, the greater the rate of cooling
In physics, what is a system?
An object or a group of objects
What is meant by the dissipation of energy?
Energy becomes stored in non-useful ways (usually the thermal store of the surroundings)
What are the effects of thickness of the walls of a building on the rate of cooling?
The thicker the wall, the smaller the rate of cooling
What are the changes to stored energy when an object is accelerated by a constant force?
The kinetic energy store of the object increases
What equation links changes to the gravitational potential energy, mass, gravitational field strength, and height?
Change in gravitational potential energy = mass x gravitational field strength x height
GPE = mgh
What environmental impact is there from using wind?
Wind turbines can be noisy, and are often considered an eye-sore
What are the changes to stored energy when an electric kettle brings water to the boil?
Energy is transferred to the element by electrical working and the thermal store of the element increases. Energy is then transferred to the thermal energy store of the water by heating
State the equation for efficiency
Efficiency = useful power output / total energy input
What is meant by a renewable energy resource?
One that is being (or can be) replenished as it is used
What are the changes to stored energy when an object is projected up a slope?
The kinetic energy store of the object decreases, and the gravitational potential store of the object increases
What environmental impact is there from using biofuel made from crops?
Land needed could be used to grow food. Can be close to carbon neutral as the CO2 released when burned was taken in when the plant was growing
What is the equation that links power, energy transferred, and time?
Energy transferred = power x time
E = Pt
What environmental impact is there from using hydroelectricity?
Dam needs to be built, and land flooded to make the reservoir
Explain what is meant by the conservation of energy
The total energy before a process = the total energy after a process
Suggest ways in which the efficiency of a machine could be increased
Use lubrication to reduce friction, use wires of a lower resistance
Give four examples of a non-renewable energy resource
Coal, oil, natural gas, uranium
What is meant by the term “energy resource”?
A material or mechanism used for the generation of electricity, for transport, and for heating of homes and workplaces
What are the changes to stored energy when a vehicle slows down?
The kinetic energy store of the object decreases, and the thermal energy store of the brakes increases
What unit is power measured in?
Watts (W)
What environmental impact is there from using uranium?
Uranium has to be mined, byproducts are highly radioactive and last for a long time
What are the changes to stored energy when a moving object hits an obstacle?
The kinetic energy store of the object decreases, and the thermal energy store of the obstacle and the surroundings increases
A car driver sees a fallen tree lying across the road ahead and makes an
emergency stop.
The braking distance of the car depends on the speed of the car.
For the same braking force, explain what happens to the braking distance if the
speed doubles.
You should refer to kinetic energy in your answer.
- doubling speed increase the kinetic energy
- kinetic energy increases by a factor of 4
- work done (by brakes) to stop the car increases
- work done increases by a factor of 4
- work done is force × distance and braking force is constant
- so if work done increases by 4 then the braking distance must increase by 4
Give one environmental advantage to turning off electrical appliances when
they are not being used.
e.g.
- conserves fossil fuels
- less (fossil) fuels burned
- less pollutant gas (produced)
- less greenhouse gas (produced)
