Topic 3 - Conservation of energy Flashcards
What is the equation for change in gravitational potential energy?
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
What is the equation to calculate the amounts of energy associated with a moving object?
kinetic energy (joule, J) = 1/2 x mass (kilogram, kg) x (speed)² (m/s) ²)
How would you draw a diagram to represent an energy transfer?
Have an arrow/s pointing towards a box labelled as the object and arrow/s pointing out of the box. The arrow pointing in is the energy input and the one/s pointing out is the energy output (including the waste output energy)
Explain what is meant by conservation of energy
Energy can be transferred usefully, stored or dissipated but it can’t be created or destroyed.
Analyses the changes involved in the way energy is stored when an object is projected upwards
Kinetic energy is transferred to gravitational potential energy, then vice versa as it falls back down
Analyses the changes involved in the way energy is stored when an object is projected up a slope
Kinetic energy is transferred to gravitational potential energy (and also to heat if friction is present)
Analyses the changes involved in the way energy is stored when a moving object hits an obstacle
Kinetic energy is transferred to sound. It is also transferred to the obstacle if it moves too.
Analyse the changes involved in the way energy is stored when a object is being accelerated by a constant force
The object is having work done to it, with it gaining kinetic energy.
Whatever supplies the force is having its energy transferred to kinetic energy.
Analyses the changes involved in the way energy is stored when a vehicle slows down
Kinetic energy is transferred to heat through the brakes
Analyses the changes involved in the way energy is stored when bringing water to a boil in an electric kettle
Electrical energy is transferred to thermal energy
Explain closed systems
The total energy of an isolated system remains constant. A ‘closed system’ has no external forces acting on it. Therefore, there is no net change to the total energy regardless of the energy transfers that take place.
Describe waste energy
In all system changes energy is dissipated so that is stored in less useful ways. Often through, light, sound or (most commonly) heat
Explain mechanical waste energy
-In mechanical processes (where forces are involved on objects) energy transferred to it can cause a rise in temperature.
-So energy is dissipated to surroundings, which makes the process wasteful.
Explain how to reduce unwanted energy transfers
-Lubricating systems so that less friction and less heat is created
-Thermal insulation, so less heat is lost to surroundings
Describe the effects of the thickness and thermal conductivity of the walls of a building on its rate of cooling qualitatively
-Thicker walls mean greater thermal insulation, so less heat is lost.
-Air cavities between walls cause lots of heat loss by convection - cavity wall insulation fills in this gap and prevents air flow
What is the equation for efficiency?
efficiency = useful energy transferred by the device/total energy supplied to the device
Explain how efficiency can be increased
-By reducing waste output (via lubrication/thermal insulation)
-By recycling waste output and using it as input (e.g. absorbing heat energy dissipated and using it as input heat energy)
Analyse fossil fuels
-Includes coal, oil and gas
Pros:
-Easy to store
-Oil is readily available and we currently have a large supply of gas
Cons:
-Non-renewable
-Produces greenhouse gases
Analyse nuclear fuel
Pros:
-Low fuel quantity generates large amounts of energy
-Low cost
-Produces no polluting gases
-Plentiful
Cons:
-Radioactive waste is difficult and expensive to dispose of
-Thermal pollution from waste water affects marine life
-Difficult to extract/purify
Analyse bio-fuel
Pros:
-Renewable
-Reduces the need for landfill space
-Creates jobs
Cons:
-Expensive to produce
-Takes up land that could be used for food production
-May increase deforestation
Analyse wind energy
Pros:
-Renewable
-Low operating costs
Cons:
-Noise and visual pollution
-Intermittent
-Can disrupt habitats and harm flying animals
Analyse hydroelectricity
Pros:
-Renewable
-Can support intermittent energy sources
-Produced domestically
Cons:
-Expensive up-front
-Disrupts river systems
-Relies on local weather and precipitation
Analyse the tides as an energy source
Pros:
-Renewable
-Tidal turbines turn slowly so wildlife harm is minimised
-Constantly reliable
Cons:
-Can alter habitats and migration patterns
-Currently expensive and has limited sites
-At early research stage and doesn’t generate much yet
Analyse solar energy
Pros:
-Renewable
-Cheap to run
-Can generate electricity even with no connection to the national grid
Cons:
-Not very efficient
-Expensive to make them more efficient
-Unreliable (not constant)
Compare the ways in which renewable and non-renewable sources are used
Non-renewable energy is used more for large-scale energy supplies due to the large energy output per kg of fuel - renewable resources cannot provide such a large amount of energy as easily.
Explain the patterns and trends in the use of energy resources
-During the industrial revolution, fossil fuels became an important source of energy as it was easy to mine, and provided a lot of energy
-Only recently has renewable energy become more suitable as technology has developed to be able to harness such energy sources efficiently
