AQA Physics paper 1 Graded A

Energy is transferred between stores - Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, nuclear Energy is transferred... - Mechanically (by a force doing work), electrically (work done by moving charges), by heating or by radiation (like light or sound) When a system changes, energy is transferred - It can be transferred into or away from the system, between objects in the system or between different types of energy stores. Closed systems are where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always 0 kinetic energy - energy of motion - the greater an object's mass and the faster it is going, the more energy there will be in its kinetic energy store. Ek (j) = 1/2m(kg)v(m/s) squared Raised objects store energy in gravitational potential energy stores - lifting an object in a gravitational field requires work, causing an energy transfer to the the GPE store of the object. Ep(j) = m(kg)g(n/kg)h(m) Falling objects transfer energy - Falling objects transfer energy from its GPE store to its kinetic energy store. When there's no air resistance, energy lost from the GPE store = energy gained in the kinetic energy store Stretching transfers energy to elastic potential energy stores - As long as the limit of proportionality has not been exceeded, Ee (j) = 1/2 k (N/m) e (m) squared specific heat capacity - the energy required to raise the temperature of one gram of a substance by one degree Celsius. E (j) = m(kg) c(j/kgdegree) theta (degrees Celsius) Conservation of energy principle - Energy can be transferred but can never be created of destroyed Dissipated energy - energy used up in a system, typically lost due to work done by friction, 'wasted energy' Phone energy - When you use the phone, energy is usefully transferred from the chemical energy store of the battery in the phone, but some of this energy is dissipated to thermal energy Closed system energy transfer - A cold spoon is dropped into hot soup in an insulated flask, which is then sealed. Energy is transferred from the thermal energy store of the soup to the useless thermal energy of the spoon Power - The rate at which work is done (watts). P(w) = E(j) / t(s) Powerful machine - One which transfers a lot of energy in a short space of time Conduction occurs mainly in solids - Conduction is the process where vibrating particles transfer energy to neighbouring particles. Long definition of conduction - Energy transferred to an object by heating is transferred to the thermal store, which is shared across the kinetic store of the particles. The particles' collisions cause energy to be transferred between particles kinetic energy stores. thermal conductivity - the Mrs sure of the rate at which thermal energy can travel through a material Convection occurs only in liquids and gases - Convection is where energetic particles move away from hotter to cooler regions Convection longer definition - Unlike in solids, the particles in liquids and gases are able to move. When you heat a region of a gas/liquid, the particles move faster and the space between particles increases. This causes the density of the region to decrease. Because they can flow, the warmer and less dense region will rise above denser cooler regions. If there is a constant heat source, a convection current will be made Radiators - convection currents - Energy is transferred from the radiator to nearby air particles by conduction. The air by the radiator becomes warmer and less dense. This warm air rises and is replaced by cooler air. At the same time, the previously heated air transfers energy to the surrounding and cools, becomes denser, and sinks. This cycle repeats and causes a flow of air to circulate around the room How to reduce unwanted energy transfers - Lubrication and thermal insulation Lubrication reduces frictional forces - When something moves, there's at least one frictional force acting on it, causing some energy to be dissipated. For objects that are rubbed together, lubricants reduce the fiction between the object's surfaces when moved. Lubricants tend to be liquids (like oil) to flow easily between objects and coat them Insulation reduces the rate of energy transfer by heating - Things to do to prevent energy loss through heating...