P1- Energy

• what is a system?

  A system is an object or group of objects.
• There are changes in the way energy is stored when a system changes
• Students should be able to describe all the changes involved in the way energy is stored when a system changes, for common situations
• examples of all the changes involved in the way energy is stored when a system changes:

  • an object projected upwards

  • a moving object hitting an obstacle

  • an object accelerated by a constant force

  • a vehicle slowing down

  • bringing water to a boil in an electric kettle
• students should be able to calculate the changes in energy involved when a system is changed by:

  • heating

  • work done by forces

  • work done when a current flows
• use calculations to show on a common scale how the overall energy in a system is redistributed when the system is changed.
• Students should be able to calculate the amount of energy associated with a moving object, a stretched spring and an object raised above ground level.
• The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
• Required practical activity 14: an investigation to determine the specific heat capacity of one or more materials. The investigation will involve linking the decrease of one energy store (or work done) to the increase in temperature and subsequent increase in thermal energy stored.
• Power is defined as the rate at which energy is transferred or the rate at which work is don
• power, P, in watts, W
• energy transferred, E, in joules, J
• time, t, in seconds, s
• work done, W, in joules, J
• An energy transfer of 1 joule per second is equal to a power of 1 watt.
• Students should be able to give examples that illustrate the definition of power eg comparing two electric motors that both lift the same weight through the same height but one does it faster than the other.
• Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
• Students should be able to describe with examples where there are energy transfers in a closed system, that there is no net change to the total energy.
• Students should be able to describe, with examples, how in all system changes energy is dissipated, so that it is stored in less useful ways. This energy is often described as being ‘wasted’.
• Students should be able to explain ways of reducing unwanted energy transfers, for example through lubrication and the use of thermal insulation
• The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.
• Students should be able to describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls.
• Students do not need to know the definition of thermal conductivity.
• Students should be able to describe ways to increase the efficiency of an intended energy transfer
• The main energy resources available for use on Earth include: fossil fuels (coal, oil and gas), nuclear fuel, bio-fuel, wind, hydroelectricity, geothermal, the tides, the Sun and water waves.
• A renewable energy resource is one that is being (or can be) replenished as it is used.
• The uses of energy resources include: transport, electricity generation and heating.
• Students should be able to:

  • describe the main energy sources available

  • distinguish between energy resources that are renewable and energy resources that are non-renewable

  • compare ways that different energy resources are used, the uses to include transport, electricity generation and heating

  • understand why some energy resources are more reliable than others

  • describe the environmental impact arising from the use of different energy resources

  • explain patterns and trends in the use of energy resources
• Students should be able to: • consider the environmental issues that may arise from the use of different energy resources • show that science has the ability to identify environmental issues arising from the use of energy resources but not always the power to deal with the issues because of political, social, ethical or economic considerations
• Internal (thermal) store

  • The internal store of energy is the sum of the kinetic energy stored in the particles of an object and the chemical energy stored in chemical bonds between particles in the object.
• Internal energy and temperature

  • The temperature of a body (object) is a measure of the energy in the kinetic stores of its particles.
  • Increasing a body’s temperature increases the energy in the kinetic stores of the body’s particles, which means that the energy in the body’s internal store also increases.
• what is internal energy?

  The amount of energy in an object’s internal energy is the sum (total) of the kinetic energy and potential energy stored in the object's particles.
• The kinetic energy (measured in joules) is equal to half the mass (in kilograms) multiplied by the velocity (in metres per second) squared.
• The elastic potential energy (measured in joules) is equal to half the spring constant (in Newtons per metre) multiplied by the extension (in metres) squared.