Kinetic & Potential Energy Stores

• Movement means energy in an object's kinetic energy store
• Energy is trasnferred to the kinetic energy store when an object speeds up and is transferred away from this store when an object slows down
• The energy in the kinetic energy store depends on the object's mass and speed
• The greater an object's mass and the faster it is going, the more energy there will be in its kinetic store
• Kinetic energy(J) = 1/2 x mass(kg) x speed^2((m/s)^2)
• Ek(J) = 1/2m(kg)^2((m/s)^2)
• A car of mass 2500kg is travelling at 20 m/s. Calculate the energy in its kinetic energy store. Ek = 1/2 x 2500 x 20^2 = 500 000J
• Raised objects store energy in gravitational potential energy stores
• Lifting an object in a gravitational field requires work. This causes a transfer of energy to the gravitational potential energy (g.p.e.) storeof the raised object
• The higher the object is lifted, the more energy is transferred to the gravitational potential energy store
• The amount of energy in a g.p.e. store depends on the object's mass, its height and the strength of the gravitational field of the object is in
• g.p.e(J) = mass(kg) x gravitational field strength(N/kg) x height(m)
• Ep(J) = m(kg)g(N/kg)h(m)
• When something falls, energy from its gravitational potential energy store is transferred to its kinetic energy store
• For a falling object when there's no air resistance: Energy lost from g.p.e. store = Energy gained in the kinetic energy store
• In real life, air resistance acts against all falling objects - it causes some energy to be transferred to other energy stores e.g thermal energy stores of the object and surroundings
• Stretching can transfer energy to elastic potential energy stores
• So long as the limit of proportionality has not been exceeded, energy in the elastic potential energy store of a stretched spring can be found using the elastic potential energy formula
• Elastic potential energy(J) = 1/2 x spring constant(N/m) x extension^2(m)
• Ee(J) = 1/2k(N/m)e^2(m)