Unit 3 - Physics: Motion, energy and electricity. Flashcards
State that there are two types of charges
Positive
Negative
Unlike charges….
Like charges….
Unlike charges attract
LIke charges repel
Describe an electric field
A region in which an electric charge experiences a force.
Define speed and calculate speed from total time/total distance
The rate at which an object covers distance. How fast an object’s distance is changing.
S = d/t
Plot and interpret a speed/time graph and a distance/time graph
.
Recognise from the shape of a speed/time graph when a body is
- at rest
- moving with constant speed
- moving with changing speed
.
Distance travelled is the area under the graph.
Recognise liner motion for which the acceleration is constant and calculate the acceleration.
Straight line graph
Recognise motion for which the acceleration is not constant
Smooth curve graph.
Calculate the area under a speed/time graph to work out the distance travelled for motion with constant acceleration.
Area = distance travelled
Give and identify examples of energy in different forms, including kinetic, gravitational, chemical, nuclear, thermal (heat), electrical. light and sound.
Kinetic: person running Gravitational potential: swings. Books on shelves Chemical: food. Fuel. Batteries Nuclear: fission. Fussion. Thermal: heater Electrical: TV, video games Light: light bulb Sound: voices, instruments.
What is -energy -work -power measured in.
Energy = joules (J)
Work done = joules (J)
Power = Watts (W)
Demonstrate understanding that an object may have energy due to its motion (kinetic) or its position (potential), and that energy may be transferred and stored.
Gravitational potential energy is work done against gravity. If an object is raised up, work is done against gravity. If the object then falls, the energy is converted into kinetic energy. ie gravitational potential at the top = kinetic energy at the bottom
Kinetic energy equation
K.E. = 1/2mv^2
= 1/2 x mass x velocity^2
Potential energy equation
P.E. = mgh
= mass x gravity x height.
Give and identify examples of the conversion of energy from one form to another, and of its transfer from one place to another.
Eg pool
The pool cue has kinetic energy while moving towards the ball. When it hits the ball, the kinetic energy is transferred into sound, heat and kinetic energy.
Apply the principle of energy conservation to simple examples
The Law of Conservation of Energy
“Energy cannot be created nor destroyed, merely converted from one type into another”
Demonstrate a qualitative understanding of efficiency
Whenever a machine operates energy is transferred from one form into another. Some energy will also be lost (sound, heat by friction etc). Obviously the less energy converted into the desired type then the less efficient the machine is.
Eg something that is 85% energy efficient will waste 15% of the energy supplied.
Efficiency equation
Efficiency = (useful energy)/(total energy) x 100%
Distinguish between renewable and non-renewable sources of energy
Renewable = replenish-able and limitless resources eg solar, wind Nonrenewable = will eventually run out, cannot be replenished.
What is the source of energy for all our energy resources (except geothermal and nuclear)?
The Sun.
Relate (Without calculation) work done to the magnitude of a force and the distance moved.
When a force moves an object through a distance, energy is converted and work is done.
Greater the force/distance, more work is done.
Work done equation
Work done = f x d
= force x distance
or work done = power x time
Power equation
P = work done / time
= (force x distance) / time
or
P = E/t
= energy/time
Describe how electricity or other useful forms of energy may be obtained from
- chemical energy stored in fuel
- water, including the energy stored in waves, in tides and in water behind hydroelectric dams
- geothermal resources
- heat and light from the sun (solar cells and panels)
Fossil fuels
- Fuels are burnt in power stations
- Heat is used to turn water into steam
- Moving steam is used to spin a turbine, generating electricity
- Chemical -> heat -> kinetic -> electric
Wave power
- Waves are created by the wind
- They are channeled into a narrow chamber
- Air is pushed in and out of the chamber spinning a turbine.
- Kinetic -> electrical
Tidal
- Gravitational pull of the Sun and moon causing the rising and falling tides in our seas and oceans
- a rising is used to fill a reservoir
- The reservoir is then emptied, spinning a turbine, generating electricity.
- Gravitational potential -> kinetic -> electrical
Dams
- Water is collected behind dams in large reservoirs
- This is either up a hill or on a fast flowing river
- The water is released and is used to drive a turbine
- Gravitational potential -> kinetic -> electrical
Geothermal
- Rocks deep underground are hot
- Water can be pumped down to these rocks and heated up
- If steam is produced it can be used to drive a turbine
- This energy can be used to drive a turbine
- Heat -> kinetic -> electrical
- Or hot water can be used for heating
The sun
- If sunlight falls on a solar panel the energy is transformed into electricity
- When sunlight hits a surface it is transformed into heat energy
- or hot water can be used for heating
- Light -> heat or light -> electricity
- solar panels can heat water
- solar cells can transfer light energy directly into electricity
Give advantages and disadvantages of each method in terms of reliability, scale and environmental impact
- Fossil fuels
- tidal
- wave
- dams
- geothermal
- solar
FOSSIL FUELS
- Reliable
- Cheap
- Efficient
- non-renewable
- combustion produces carbon dioxide and other pollutants
- pollution may cause global warming
TIDAL
- renewable
- clean
- only works when there are tides
- barrages are expensive to build
- some impact through barrier installation can disrupt tidal flow to shore and hence the movement of nutrients and organisms
WAVE
- renewable
- clean
- works only if there are waves
- a large number of buoys are needed to generate enough electricity for a town. Only woks where there are big waves
DAMS
- renewable
- clean
- if there is good rain supply there will always be water to produce energy
- only suitable for hilly areas with rivers
- some impact on diverting rivers. This may upset the ecology of the area or the fertility of surrounding land.
GEOTHERMAL
- renewable
- it is free and available day and night
- clean
- only available in certain parts of the world.
- Sometimes poisonous gases are given off
- some impact from the installation of the equipment that is needed to direct steam to turbines
SOLAR
- renewable
- freely available whenever the sun is shining
- solar panels require continuous sunshine, unless the energy can be stored in batteries.
- Solar cells are expensive to buy
- some impact as may need large area for solar cells.
Describe energy changes in terms of work done
Whenever a force makes something move, work is done. The amount of work done is equal to the amount of energy transferred. Work, like energy, is measured in joules. When work is done by something, it loses energy; when work is done on something it gains energy.