Physics Chapter 1 Energy Transfers Flashcards
What is a system?
A system is an object or group of objects.
What is a closed system?
A system where energy cannot enter or leave.
In terms of energy, what happens when a system changes?
Energy must transfer from one store to another along an energy pathway.
What are the units of energy? (Units and Symbol)
Joules (J)
State the 8 energy stores
Gravitational Potential Energy (GPE)
Kinetic Energy (KE)
Elastic Potential Energy
Thermal (Internal)
Chemical
Magnetic
Electrostatic
Nuclear
Describe how the gravitational potential energy store can increase or decrease.
Increase - Object raised higher above ground (higher in gravitational field)
Decrease - Object lowered (closer to centre of gravitational field)
Describe how the kinetic energy store can increase or decrease.
Increase - Object speeds up (or becomes heavier)
Decrease - Object slows down (or becomes lighter)
Describe how the elastic potential energy store can increase or decrease.
Increase - An object is stretched or squashed (deformed) in such a way that it would return to its original shape if the force was removed.
Decrease - The size of the deformation is reduced, so the object is closer to its original shape.
Describe how the thermal (internal) energy store can increase or decrease.
Increase - Increase in temperature or a change of state (solid→liquid→gas)
Decrease - Decrease in temperature or a change in state (gas→liquid→solid)
Describe how the chemical energy store can change.
Through chemical reactions.
Describe how the magnetic energy store can change.
Changes to the strength, or location within a magnetic field.
Describe how the electrostatic energy store can change.
Transfer of charges or changes to an electric field.
Describe how the nuclear energy store can change.
Changes in the nucleus of atoms.
Give an example of a chemical energy store.
Fuel
Food
Batteries
State the principle of conservation of energy.
Energy cannot be created or destroyed, only transferred from one store to another along an energy pathway.
Name the four energy pathways.
Mechanical (Forces)
Radiation (Waves)
Electrical
Heating
What is work done.
A measure of energy transferred.
State the equation that links work done, force, and distance in words and symbols.
Work done = Force x Distance
W=Fd
(Could also use W=Fs, where s is displacement)
State the units of work done.
Joules (J)
Rearrange the formula for work done to make Force, and then Distance the subject of the equation.
F=Wd
d=WF
What is meant by useful energy?
Energy that is transferred to the store, or along the pathway, that is its intended function.
What is meant by wasted energy?
Energy that is transferred to a store, or along a pathway, that does not support the action. This is usually the thermal store of the surroundings.
What is dissipated energy?
Wasted energy that spreads out into (the thermal store of) the surroundings.
State the formula for efficiency of a device in terms of both energy and power.
Efficiency = Useful energy outputTotal energy input(100%)
Efficiency = Useful power outputTotal power input(100%)
Give some examples of how to reduce unwanted energy transfers.
Thermal insulation
Lubrication
Design for less energy lost through noise or heat
Define Power
Power is energy transferred (work done) per second.
Or Power is rate of energy transfer.
State the equation linking Power, Energy and Time in both words and units
Power = EnergyTime
P=Et
State the units of Power
Watts (W)
What does 1 Watt mean?
An energy transfer of 1 Joule per second.
Compare the power of two electric motors that both lift the same weight through the same height, but one does it faster than the other.
The one which does it faster has the greater power.
Describe how energy can be transferred by conduction.
Vibrations (kinetic energy) in particles pass energy on to neighbouring particles through collisions.
What does high thermal conductivity mean?
There is a high rate of energy transfer by conduction across the material.
What sort of materials make good thermal conductors and why?
Metals - lots of delocalised electrons to pass on collisions
Solids - particles are packed close together
What sort of materials make good thermal insulators and why?
Wood, plastics, ceramics - electrons are tightly bound within chemical bonds
Gases - particles are spread out
Vacuums - Conduction cannot occur in a vacuum
Describe how energy can be transferred by convection.
Increased vibrations (kinetic energy) in hot particles of a liquid or gas cause particles to spread out, decreasing their density and making them ‘float’ on colder fluid.
a.k.a. ‘Heat rises’
What is meant by a fluid?
A liquid or a gas
Describe how energy can be transferred by radiation.
Energy is transferred as waves emitted by all objects.
Which of the three heating energy transfers can occur in a vacuum?
Radiation - As it does not require particles.
Which of the three heating energy transfers cannot occur in solids?
Convection - As particles need to be able to move (flow).
What factors affect the rate of cooling of a building?
The thickness and thermal conductivity of its walls.
Levels of insulation
Double glazing
Opening/closing doors and windows
In the insulation required practical, what is the independent variable?
Either:
Thickness of insulating material (continuous)
Number of layers of insulating material (discrete)
Type of insulating material (categoric)
In the insulation required practical, what is the dependent variable?
Rate of cooling, or, rate of thermal transfer.
State what variables must be controlled?
Mass or volume of water
Starting temperature of water
Temperature of surroundings
Shape of container
