Energy Stores and TransfersAQA GCSE Physics: Flashcards

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What is a system in physics?

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What is a system in physics?: An object or group of objects.
Describe the energy changes when a vehicle slows down.: Kinetic energy store decreases; thermal energy stores of the brakes and surroundings increase.
Give the three ways energy can be transferred to or from a system.: By heating, by work done by a force, or by work done when a current flows.
State the equation for kinetic energy.: Ek = ½mv² (mass in kg, speed in m/s, energy in J).
State the equation for elastic potential energy.: Ee = ½ke² (k = spring constant in N/m, e = extension in m) - valid within the limit of proportionality.
State the equation for gravitational potential energy.: Ep = mgh (g given in the exam, h = height in m).
State the equation for change in thermal energy.: ΔE = mcΔθ (c = specific heat capacity, Δθ = temperature change).
Define specific heat capacity.: The energy required to raise the temperature of 1 kg of a substance by 1°C.
Define power.: The rate of transfer of energy, or the rate of doing work: P = E/t = W/t.
Two motors lift the same weight to the same height, but Motor A takes 4 s and Motor B takes 8 s. Which is more powerful?: Motor A - it transfers the same energy in less time, so has greater power.
A ball is thrown upwards. Describe the energy stores involved.: Kinetic energy store decreases as gravitational potential energy store increases, until the ball momentarily stops; then it reverses on the way down.
What is meant by 'energy is redistributed' when a system changes?: The total amount of energy stays the same, but it moves between different energy stores rather than being created or destroyed.