P2a (part 2)

Work DoneWhen a force moves an object through a distance, energy is transferred and work is done when something moves something else is providing energy to do so The thing putting in energy needs s supply of energy (e.g electricity) It does the work by moving an object Energy is transferred Whether energy is usefully transferred or wasted work is still done

Gravitational Potential Energy measured in joules (j) On Earth always have gravity acting on us When we are above the Earth’s surface we have potential (stored) energy gravitational potential energy The amount of gravitational potential energy an object on Earth has depends on its mass and height above the ground On earth gravity is 10 N/kg

Kinetic Energy Energy of movement All moving objects have it Kinetic energy of an object has depends on its mass and speed Measured in joules

Kinetic Energy Transferredis work done  moving car has lots of kinetic energy To slow down this energy needs t be converted to something else To stop a car kinetic energy is transferred into heat energy as friction

Falling objects convert kinetic energy to potential energyTe further it falls the faster it goesKinetic energy gained = potential energy lost

Power A measure of how quickly work is being done  and so how quickly energy is being transferred.

Forces and Elasticity Work done to an elastic object is stored as elastic potential energy If you apply force you might cause an object to stretch and change shape After the force has been removed the object can return to it's original shape If it can do this it is an elastic object Work is done to an elastic object to make it change shape Energy is not lost, but stored as elastic potential energy This potential energy is converted to kinetic when the force is removed e.g. a spring bouncing back into position

Hooke's Law When an elastic object - such as a spring - is stretched, the increased length is called its extension. The extension of an elastic object is directly proportional to the force applied to it: F = k × e F is the force in newtons, N k is the 'spring constant' in newtons per metre, N/m e is the extension in metres, m This equation works as long as the elastic limit (the limit of proportionality) is not exceededIf a spring is stretched too much, for example, it will not return to its original length when the load is removed The spring constant The spring constant k is different for different objects and materialsIt is found by carrying out an experimentFor example, the unloaded length of a spring is measuredDifferent numbers of slotted masses are added to the spring and its new length measured each timeThe extension is the new length minus the unloaded length Assuming the limit of proportionality (elastic limit) is not exceeded, a graph of force against extension produces a straight line that passes through the originThe gradient of the line is the spring constant, k. The greater the value of k, the stiffer the spring

Calculating power Here is the equation which relates power to work done (or energy transferred) and time: P is the power in watts, W E is the work done (or energy transferred) in joules, J t is the time taken in seconds, s. For example, an electric drill transfers 3000 J in 15 s. What is its power? Power = 3000 ÷ 15 = 200 W

Momentum A moving object has momentum The tendency of the object to keep moving in the same direction It is difficult to change the direction of movement of an object with a lot of momentum Measured in kg m/s Direction momentum doesn't just depend on the object’s mass and speed Velocity is speed in a particular direction, so the momentum of an object also depends on the direction of travel This means that the momentum of an object can change if: The object speeds up or slows down The object changes direction

Work and potential Energy

Kinetic Energy

Elasticity and Power

Momentum