Physics EOY- Conservation Of energy
Energy Sources/ Transfers and Stores
Gravitational potential Energy
Energy Transfers & Stores
Energy is a quantity that is conserved - it cannot be created or destroyed. Energy can be stored and transferred.
Stores
Kinetic Energy Store- A runner has more energy in their kinetic energy store when they are running faster.- The amount of energy in the kinetic energy store depends on the speed of the object.
GPE Store- A box has more energy in its gravitational potential energy store when it is placed on a higher shelf.- The amount of energy in the gravitational potential energy store depends on the height of the object.
Thermal Energy- An object has more energy in its thermal energy store when it is hot than when it is cold.- The amount of energy in the thermal energy store depends on the temperature of the object.
Chemical Energy- Batteries, foods and fuels store energy in their chemical energy stores. The candle wax in the picture is a type of fuel.- Transfer of energy from the chemical energy store occurs due to chemical reactions.
Elastic Potential Energy- A stretched or squashed object has more energy in its elastic energy store.- The amount of energy in the elastic energy store depends on the amount of extension or compression
When transfers take place in a system: the total energy stored before = total energy stored after.
Transfers
Kinetic Energy
Efficiency
Energy can be transferred by:
Mechanical working – when a force is applied to move an object through a distance
Electrical working – when charge flows (electricity)
Heating – when energy is transferred between hotter and colder regions
Radiation – when energy is transferred as a wave, for example as light or sound
Energy Sources
Nearly everything requires energy and a way to use energy is by transferring it from one energy store to another. Systems that can store large amounts of energy are called energy resources. The major energy resources available to produce electricity are fossil fuels, nuclear fuel, biofuel, wind, hydroelectricity, geothermal, tidal, water waves and the Sun.
During the Industrial Revolution, advances in automation and transport caused a significant increase in the amount of fossil fuels extracted and burnt.
In the 20th century, electricity became a convenient way of distributing energy that can be used for a wide range of devices and applications such as lighting, heating, computing technologies and operating machinery.
The energy Sources are; Waves, Fossil fuels, Nuclear Fuels, Biofuel, Wind, Hydroelectricity, Geothermal, Tides and Sun
The amount of gravitational potential energy stored by an object at height can be calculated using the equation:
change in gravitational potential energy = mgΔh
Change in gravitational potential energy (ΔGPE) is measured in joules (J)
Mass (m) is measured in kilograms (kg)
Gravitational field strength (g) is measured in newtons per kilogram (N/kg) It is also 10N/KG on Earth
Change in vertical height (Δh) is measured in metres (m)
The amount of kinetic energy of a moving object can be calculated using the equation:
Kinetic Energy=1/2mv^2
Kinetic energy (KE) is measured in joules (J)
Mass (m) is measured in kilograms (kg)
Speed (v) is measured in metres per second (m/s)
Devices are designed to waste as little energy as possible. This means that as much of the input energy as possible should be transferred into useful energy stores.
Percentage of Efficiency= (Useful energy Transferred / Total energy Supplied ) * 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.
Devices waste energy for various reasons, including friction between their moving parts, electrical resistance, and unwanted sound energy. In general, it is useful to increase the efficiency of any process or device. 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.