Physics - Forces and Motion + Energy Resources and Transfers

Energy Store

Energy Transfer

Kinetic

Moving objects have energy in their kinetic store

Gravitational

Objects gain energy in their gravitational potential store when they are lifted through a gravitational field

Elastic

Objects have energy in their elastic potential store if they are stretched, squashed or bent

Magnetic

Magnetic materials interacting with each other have energy in their magnetic store

Electrostatic

Objects with charge (like electrons and protons) interacting with one another have energy in their electrostatic store

Chemical

Chemical reactions transfer energy into or away from a substance’s chemical store

Nuclear

Atomic nuclei release energy from their nuclear store during nuclear reactions

Thermal

All objects have energy in their thermal store, the hotter the object, the more energy it has in this store

Mechanical Working

When a force acts on an object (eg. pulling, pushing, squashing, stretching)

Electrical Working

A charge moving through a potential difference (eg. current)

Heating (by particles)

Energy is transferred from a hotter object to a colder one (eg. conduction)

(Heating by) radiation

Energy transferred by electromagnetic waves

Principle of conservation of energy

Energy cannot be created or destroyed, only transferred from one store to another

Formula for Efficiency

efficiency = (useful energy output/total energy input) x100

Conduction

The main method of energy transfer by heating in solids

Convection

The main way that thermal energy is transferred through liquids and gases

Radiation

• All bodies (objects), no matter what temperature, emit infrared radiation

• The hotter object, the more infrared radiation it radiates in a given time

Effect of Black on absorbing and emitting ability

Absorbing: Good

Emitting: Good

Effect of Dull/dark surfaces on absorbing and emitting ability

Absorbing: Reasonable

Emitting: Reasonable

Effect of White on absorbing and emitting ability

Absorbing: Poor

Emitting: Poor

Effect of Shiny surfaces on absorbing and emitting ability

Absorbing: Very poor

Emitting: Very poor

Ways of reducing unwanted Conduction

Use materials of low conductivity (INSULATORS)

Ways of reducing unwanted Convection

• Prevent convection currents from forming

• The fluid must be prevented from moving

Insulation

• Reduces thermal conductivity

• The more dense the insulator the more conduction can occur - in denser material, the particles are closer together so they can transfer energy to one another more easily

• The thicker the material the better it will insulate

Energy Resources

Large stores of energy that can be used to generate electricity and heat homes and businesses

Energy transfers involved in generating electricity using Wind and Water

• A turbine is turned which turns a generator which generates electricity

• Energy in the kinetic store of the flowing wind/water is transferred to the kinetic store of the turbine, then to the kinetic store of the generator and transferred electrically to the National Grid

Energy transfers involved in generating electricity using Fossil Fuels

• Can be combusted to heat water and the steam produced can be used to turn turbines

• Energy from the chemical store of the fuel is transferred to the thermal storeof the water, which is then transferred to the kinetic store of the turbine, and then transferred to the kinetic storeof the generator and then transferred electrically to the National Grid

Energy transfers involved in generating electricity using Nuclear Power

• Can also be used to heat water to produce steam to turn turbines

Nuclear store of fuel → thermal store of water → kinetic store of turbine → kinetic store of generator

Energy transfers involved in generating electricity using Geothermal Resources

• Geothermal energy is another way to produce the steam that turns the turbines

• Water is pumped down to the hot rocks and returns through a fissure as steam

Advantages and disadvantages of methods of large-scale electricity production from various renewable and non-renewable resource

Energy resource	Renewable?	Advantages	Disadvantages
Fossil fuels	No	Reliable. Can produce large amounts of energy consistently. Can respond to changes in demand.	Produces carbon dioxide (CO2) which contribute to global warming, and sulphur dioxide, which causes acid rain
Nuclear	No	Reliable. Produces large amounts of energy consistently. Produces no pollution or CO2. Large amounts of energy are produced from small amounts of fuel.	Produces radioactive waste that takes thousands of years to decay and must be safely disposed of. Nuclear power stations are expensive to build and maintain, and take many years to build. Can not be turned on and off quickly so cannot respond to changes in demand.
Bio fuels	Yes	The CO2released from combustion is balanced by the CO2 absorbed in photosynthesis, so could be considered carbon neutral	Land and resources used to grow crops are needed to grow food crops
Wind	Yes	Produces no pollution or CO2. Are cheap to build and maintain	Non-reliable. Only generate electricity when the wind is blowing in a certain direction. Some people consider them visual pollution (they spoil the view)
Hydroelectric	Yes	Reliable. Can respond to meet changes in demand. No pollution or CO2 produced (unless a pump is used to return the water as this uses fossil  fuels).	Can involve flooding large areas to build reservoirs which destroys habitats and displaces wildlife
Tidal	Yes	Tides are very predictable, so energy can be produced at regular intervals	Few suitable locations (estuaries). Can harm aquatic life and disrupt shipping
Geothermal	Yes	Reliable	Not many suitable locations. Can release methane (a greenhouse gas) in the extraction process.
Solar	Yes	Produces no pollution or greenhouse gases. Good for electricity production in remote areas.

Newton’s 1st Law

An object will remain at a constant velocity unless acted upon by a net external force

Newton’s 3rd Law

For every action, there is an equal and opposite reaction

Hooke’s Law

force = spring constant x extension (f=kx)

Practical: Investigate how extension varies with applied force for helical springs, metal wires and rubber bands

What is the initial linear region of a force-extension graph associated with?

Hooke’s Law

Definition of: Elastic Behaviour

The ability of an object to recover to its original shape after the forces causing deformation have been removed

Safety Features Associated with Momentum

In a car:

• Seatbelts: brings the person to rest more slowly

• Airbags: brings the person to rest more slowly

• Crumple zones: A crumple zone increases the time-taken to come to rest for a given change in momentum here since F = Δp/t, the force decreases.

Definition of: Power

The rate of transfer of energy or the rate of doing work

Where does the weight of a body act through?

It’s centre of gravity

Principle of Moments

If an object is balanced, the total clockwise moment about a pivot is equal to the total anticlockwise moment about that pivot.

Equation Linking: Momentum, Mass and Velocity

p(kgm/s) = mv: p(momentum), m(mass), v(velocity)

Equation Linking: Force, Change in Momentum and Time Taken

F= Δp/t

Equation Linking: Moment of Force, Force and Distance to Pivot

M = Fd

Equation Linking: Work Done, Force and Distance Moved in Direction of Force

W = Fd

Formula for Calculating: Kinetic Energy

KE = 1/2 mv²

Formula for Calculating: Change in GPE

GPE = mgh: m(mass), g(gravitational field strength), h(height)

Formula for Calculating: Power

P = W/t

Formula for Calculating: Efficiency

efficiency = useful energy transferred/ total energy input