Topic 3/8 Energy Flashcards
Recall and use the equation to calculate the change in GPE when an object is raised above the ground:
change in gravitational potential energy (joule, J) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg) × change in vertical height (metre, m)
∆GPE = m× g ×∆h
Recall and use the equation to calculate the amounts of
energy associated with a moving object:
Kinetic Energy (Joules) = 1/2 * mass (kilogram, kg) * (speed)^2 ((m/s)^2)
KE = 1/2mv^2
Draw and interpret diagrams to represent energy transfers
We need to draw a sankey diagram
Useful energy goes straight but useless energy points downwards
or we could draw a transfer diagram
GPE ——-> Mechanical work by gravity inc child’s speed ——-> KE of child
There would be a box around each thing outside the arrows
Explain what is meant by conservation of energy
Energy can be transferred usefully, stored or dissipated but it cannot be created or destroyed.
Analyse the changes involved in the way energy is stored when a system changes, including:
a an object projected upwards or up a slope
When an object is projected upwards:
Explanation:- Initially, the object has kinetic energy due to its motion.
As it moves upwards, its kinetic energy decreases while its potential energy increases.
Answer: The object’s kinetic energy decreases while its potential energy increases.
Analyse the changes involved in the way energy is stored when a system changes, including:
b a moving object hitting an obstacle
When a moving object hits an obstacle:
Explanation:
The object’s kinetic energy decreases rapidly upon impact.
Some of the kinetic energy is converted into other forms such as sound, heat, and deformation energy.
Answer: The object’s kinetic energy decreases and is converted into other forms of energy.
Analyse the changes involved in the way energy is stored when a system changes, including:
c an object being accelerated by a constant force
When an object is accelerated by a (constant) force:
Explanation:
The object gains kinetic energy as it accelerates.
The work done by the force increases the object’s kinetic energy.
Answer: The object’s kinetic energy increases due to the work done by the force.
Analyse the changes involved in the way energy is stored when a system changes, including:
d a vehicle slowing down
When a vehicle slows down:
Explanation:
The vehicle’s kinetic energy decreases as it slows down.
The energy is dissipated as heat due to friction between the vehicle’s brakes and the road.
Answer: The vehicle’s kinetic energy decreases and is dissipated as heat due to friction.
Analyse the changes involved in the way energy is stored when a system changes, including:
e bringing water to a boil in an electric kettle
When water is brought to boil in an electric kettle:
Explanation:
The electric kettle transfers electrical energy into thermal energy to heat the water.
The water absorbs this thermal energy and its temperature rises until it reaches the boiling point.
Answer: Electrical energy is converted into thermal energy to heat the water.
Explain that where there are energy transfers in a closed
system there is ___ ____ ______ to the total energy in that
system
no net change
As the transfers are in a closed system, energy cannot dissipate/exchange into the surroundings
Explain that mechanical processes become wasteful when they
cause a ____ ___ ________ so dissipating energy in heating
the surroundings
rise in temperature
In a mechanical system, energy is dissipated when two surfaces rub together. Work is done against friction which causes heating of the two surfaces – so the internal (thermal) energy store of the surfaces increases and this is then transferred to the internal energy store of the surroundings.
Explain, using examples, how in all system changes energy is
dissipated so that it is stored in less useful ways
Dissipation is a term that is often used to describe ways in which energy is wasted. Any energy that is not transferred to useful energy stores is said to be wasted because it is lost to the surroundings. Electrical cables warming up are a good example of this. It is not useful to have hot wires behind a television as energy is dissipated to the surrounding air.
Explain ways of reducing unwanted energy transfer
Lubrication:
Frictional forces cause surfaces to heat up resulting in an unwanted energy transfer. Reducing the friction between two surfaces can reduce this unwanted energy transfer.
Friction is sometimes reduced by placing rollers or ball bearings between the surfaces but, most often, oil is used to lubricate the
surfaces and allow them to slide smoothly over each other.
Thermal Insulation:
Heating a house can be difficult since some energy is dissipated through the windows/walls
So people use techniques to reduce the dissipation, ie: double glazed windows, as they have a gap of air in between 2 panels of glass. Because air is a poor conductor, more heat is kept in
People also use cavity wall insulation (blowing insulating material between the brick and inside wall) This helps keep the heat trapped inside and reduces the loss by air circling inside the cavity
How does the thickness of walls affect the rate of cooling
The thicker the walls of a building, the slower its rate of cooling (1) . The lower the thermal conductivity of a building, the slower its rate of cooling (1) . The efficiency of an energy transfer can be increased by: lubrication (1) , thermal insulation (1)
Efficiency =
Useful energy/total energy * 100
Explain how efficiency can be increased
This can be achieved by reducing wasted energy transfers so more of the input energy is usefully transferred.
Mechanical devices can be made more efficient through
lubrication to reduce the friction between moving parts of a machine and increase the amount of useful energy transferred.
For systems that are designed to transfer thermal energy, the efficiency can be improved by reducing the wasteful dissipation of thermal energy to the surroundings, for example by using insulation.
Why is it not possible to have an efficiency of >100%
It is not possible to have an efficiency of greater than 1 or an efficiency percentage greater than 100%. This would mean that more energy is being transferred than is being supplied, which would mean that energy is being created. This would break the law of conservation of energy.
What are the different renewable and non renewable energy sources
Renewable resources include:
Solar energy
Wind
Bio-fuel
Hydroelectricity
Geothermal
Tidal
Non-renewable energy resources include:
Fossil Fuels (coal, oil and natural gas)
Nuclear fuel
How are fossil fuels (coal/oil/fuel) used as energy sources
Fossil fuels are combusted to heat water to produce steam to turn turbines to generate electricity
How are bio-fuels used as energy sources
Plant matter, ethanol or methane can be produced and used as a fuel in place of fossil fuels
How are nuclear fuels used as energy sources
Nuclear fuels are reacted to heat water to produce steam to turn turbines to generate electricity
How is the wind used as energy sources
Wind turns turbines directly to generate electricity
How are hydroelectrics used as energy sources
Water is stored at a height, and when released, rushing water turns turbines directly to generate electricity
How are tides used as energy sources
The movement of water due to tides turn turbines directly to generate electricity
