1) Conservation Of Energy Flashcards
What are the different energy stores?
- kinetic
- thermal
- chemical
- elastic potential
- gravitational potential
- magnetic
- nuclear
- electrostatic
What is a kinetic energy store?
When an object is moving, it has energy in its kinetic energy store, energy is transferred to the store if the object speeds up, and away if it slows down
What does the kinetic energy store depend on?
Speed and mass
What happens to the kinetic energy store if the mass doubles?
The kinetic energy store doubles
What happens to the kinetic energy store if the speed doubles?
The energy in the kinetic energy store quadruples (increases by the factor of 4)
What is the equation for kinetic energy?
KE = O.5 x mass x (speed)2
What is the equation for GPE?
GPE = M x GFS x change in vertical height
What does the conservation of energy mean?
It means that energy is never created, nor destroyed, only transferred or stored
What are the main transfers of energy and what do they mean?
- mechanically=a force acting on an object e.g. pushing, stretching
- electrically=a charge doing work e.g. charges moving round a circuit
- by heating=energy transferred from a hotter object to a colder one
- by radiation=energy transferred by waves e.g energy from the sun reaching the earth by light
What is the equation for the total energy input?
Total energy input = useful energy output + wasted energy
What is the equation for efficiency?
Efficiency = useful energy transferred by device(j) / total energy supplied to device(j)
Fact about efficiency
Some energy is always wasted, the efficiency can never be equal to or higher than 1(100%)
What are the two main ways to reduce wasted energy?
Lubrication-liquids like oil coat the object and reduce friction
Thermal insulation-reduces the rate of energy transferred by heating(conduction)
What type of diagrams show the efficiency of something?
Sankey diagrams
What are non-renewable resources and some examples
Non-renewable means they will eventually run out.
Examples: fossil fuels and nuclear energy
Advantages of fossil fuels
- They are reliable
- fossil fuel power plants are relatively cheap to build&run
- they can respond quickly to changes in energy demand
Disadvantages of fossil fuels
- they’re slowly running out
- they create environmental problems: global warming, acid rain
Advantages of nuclear power
- it’s clean apart from the waste
- it is reliable
Disadvantages of nuclear power
- the nuclear waste is very dangerous and difficult to dispose of
- nuclear power plants are pretty costly to build and safely decommission
What does renewable resources mean, and examples
Renewable energy resources will never run out.
Examples: biomass, wind, solar, hydro-electricity, tidal, wave, geothermic power
Advantages of biomass
Renewable
Carbon neutral
Fairly reliable
Disadvantages of biomass
Very costly
Could not be enough space/water for food crops
Some forests have been destroyed to create space for biomass crops to be grown-destroys habitats
What do vector quantities have
Magnitude and direction
What do scalar quantities have
Magnitude but no direction
Example of vectors
Force, velocity, weight, momentum, acceleration
Examples of scalars
Speed, energy, temp, time
WHat is displacement
Measures the distance and direction in a straight line from an objects starting point to its finishing point
What is velocity
Speed in a stated direction
Equation for average speed (m/s)
Distance (m) / time (s)
Equation for acceleration (m/s(2))
Change is velocity (m/s) / time taken (s)
What’s the equation that links initial and final velocity and acceleration
Final Velocity(2) - initial velocity(2) = 2 x acceleration x distance
What is the average speed of walking
1.4 m/s
Average speed for running
3 m/s
Average car speed (non motorway)
13 m/s
What is acceleration
How quickly you’re speeding up, the change in velocity in a certain amount of time
Average speed of wind
5-20 m/s
Average speed of sound in air
340 m/s
Average speed of cycling
5.5 m/s
What does the gradient of a distance time graph show
The speed of the object
What does the curve getting steeper on a distance time graph mean
Speeding up (increasing gradient)
What does the graph levelling off on a distance time graph mean
It’s slowing down (deceasing gradient)
How do u work out the gradient/speed from a distance time graph
Change in vertical/change in horizontal
What does the gradient mean on a velocity time graph
Acceleration
What shows the distance travelled on a velocity time graph
The area under any section of the graph, can split it into rectangles and triangles
What is Newton’s first law?
Resultant force is needed to making something start moving, speed up or slow down
What is the stopping distance
The sum of the thinking and breaking distance
What 6 factors affect stopping distance
Mass of the vehicle, sped of the vehicle, drivers reaction time, state of the vehicles breaks, state of the road, amount of friction between the tyre and the road surface
What is acceleration proportional to
The resultant force
What is acceleration inversely proportional to
The mass
What does it mean that acceleration is inversely proportional to mass
An object with a larger mass with accelerate less
Formula for Newton’s first law
Resultant force (N) = mass(kg) x acceleration (m/s(2))
What do safety features in cars increase
Collision time
What are crumple zones
Areas at the front of back of a vehicle which crumple up easily in a collision, increasing time taken to stop
What’s mass
The amount of matter in an object
What is weight
The force acting on an object due to gravity
What is force measured in
Newtons
What is the centripetal force
The force that keeps something moving in a circle
What happens as an object is travelling in an circle at a constant speed
It is constantly changing velocity so it’s accelerating, so it must have a resultant force
What different equipment can u use to measure speed
Light gates, stopwatch, rolling tape measure, take a video and look at how far the object travels each frame
What is Inertia
The tendency for motion to remain unchanged
What does an object interval mass do
Measures how difficult it is to change the velocity of an object
What is newtons 3rd law
Reaction forces are equal and opposite
What is inertia defined as
The ratio of force over acceleration
What is the unit for momentum
Kg m/s
What is momentum
The product of the objects mass and velocity
What is conservation of momentum
In a closed system the total momentum before an event is equal
To The total momentum after
What is thinking distance
The distance the car travels in the drivers reaction time
What 4 factors affect a drivers reaction time
Tiredness, alcohol, drugs, distractions
What is the braking distance
The distance taken to stop once the breaks have been applied
What are 2 ways of measuring reaction time
A computer based test, the ruler drop test
What is the typical reaction time of someone doing the ruler drop test
0.2-0.6 s
What is uniform acceleration
Constant acceleration
What is the acceleration in free fall
10 m/s
What is conservation of energy
Energy is never created or destroyed
What happens where there are energy stores
The total energy of a closed system has no net change
What are the 4 ways energy can be transferred between stores
Mechanically, electrically, by heating, by radiation
What does energy transferred mechanically mean
A force acting on an object (and doing work) e.g. pushing, stretching, squashing
What does energy transferred electrically mean
A charge doing work e.g. Charges moving around a circuit
What does energy transferred by heating mean
Energy transfer from a hotter object to a colder object e.g heating a pan on a hob
What does energy transferred by radiation mean
Energy transferred by waves e.g. energy from the sun reaching earth by light
In a diagram that shows energy transfers what do arrows represent
Transfers
In a diagram that shows energy transfers what do boxes represent
The stores
What energy transfers are going on in a ball rolling up a slope
Ball does work against the gravitational force, so energy is transferred mechanically from the KE store of the ball to its gravitational potential energy store
What energy transfers are going on in a bat hitting a ball
The bat has energy in its KE store, some of this is transferred mechanically to the balls KE store. Some is also transferred mechanically to the thermal store of the bat and ball(and to surroundings by heating) rest is carried away by sound
What energy transfers are going on in a rock dropped from a cliff
Assuming there’s no air resistance, gravity does work on the rock so the rock constantly accelerates towards the ground, e transferred mechanically from the rocks GPE store to its KE stor
What energy transfers are going on in a car slowing down (without braking)
E in the KE store of thr car is transferred mechanically (due to friction between the tyres and the road) and then by heating, to the thermal store of the car and road
What energy transfers are going on in a kettle boiling water
E is transferred electrically from mains to the heating element of the kettle then by heating to the thermal store of the water
What is another important principle
Energy is only useful when it is transferred from one store to a useful store
When do mechanical processes become wasteful
When they cause a rise in temp so dissipating energy in heating the surroundings
What can reduce energy transferred by friction
Lubrication e.g. oil
What can reduce rate of energy transfer by heating
Insulation
What do thick walls do
Slows the rate of energy transfer
What is thermal conductivity
How well a material transfers energy by conduction
What things have low thermal conductivity
Gases like air
What is a cavity wall
Made up of inner and outer walls with an air gap in the middle - air gap reduces amount of energy transferred by conduction
