Work and Potential Energy

When a force moves an object through a distance Energy is transferred and work is done
1. Whenever something moves something else is providing some sort of effort to move it
  1. The thing putting the effort in needs a supply of energy e.g. fuel
    1. It then does work by moving the object and one way or another it transfers the energy it receives (as fuel) into other forms
      1. Whether this energy is transferred or wasted you can still say that the work is done. Work done and energy transferred are the same (there both given in joules)
Work done = Force x Distance
Gravitational Potential energy is energy due to height
1. Gravitational potential energy (J) is the energy that an object has by virtue of (because of) its vertical position in a gravitational field. When an object is raised vertically work is done against the force of gravity (it takes effort to lift it up) and the object gains gravitational potential energy. On earth the gravitational field strength is 10N/kg
2. A sheep with a mass of 47kg is slowly raised through 6.3m. Find the potential energy
  1. Ep = 47 x 10 x 6.3 = 2961J
Kinetic Energy
1. Anything thats moving has kinetic energy
2. Kinetic energy = 1/2 x mass x speed squared
3. Remember the kinetic energy of something depends on both mass and speed. The more it weighs and the faster its going the bigger its kinetic energy will be
4. Kinetic energy transferred is work done
  1. When a car is moving it has kinetic energy
    1. A moving car can have a lot of kinetic energy. To slow a car down the kinetic energy needs to be converted into other types of energy
      1. To stop a car the kinetic energy has to be converted to heat energy as friction between the wheels and the brake pads causing the temperature of the brakes to increase
        Kinetic energy transferred =Work done by brakes
        1/2mv squared = F x d
        m= mass (kg), v=speed (m/s), F=maximum braking force (N), d=braking distance (m)
  2. Falling objects convert potential energy into kinetic energy
    1. When something falls its potential energy is converted into kinetic energy. So the further it falls the faster it goes
      1. kinetic energy gained = Potential energy lost
  3. Some of the kinetic energy is transferred into heat and sound
Forces and Elasticity
1. Work done to an Elastic object is stored as Elastic Potential Energy
  1. When you apply a force to an object you may cause it to stretch and change in shape
    1. Any object that can go back to its original shape after the force has been removed is an elastic object
  2. Work is done to an elastic object to change its shape. This energy is stored by the object as elastic potential energy
    1. The elastic potential energy is then converted to kinetic energy when the force is removed the objects returns to its original shape
2. Extension of an elastic object is directly proportional to force
  1. If a spring is supported at the top and then a weight is attached to the bottom it stretches
    1. The extension is directly proportional to the force
      1. The extension is measured in metres and the force in newtons
        F = k x e
        k=spring constant. It depends on the material that you are stretching (N/m)
3. This stops working when the force is great enough
  1. Theres a limit to the amount of force you can apply to an object for the extension to keep on increasing proportionally
    1. For small forces force and extension are proportional.
    2. There is a maximum force that the elastic object can take and still extend proportionally. This is known as limit of proportionality

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Work and Potential Energy

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