Energy

• Energy


  Never created or destroyed, only transferred between different forms and objects
• Forms of energy


  • Thermal or internal energy
  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
  • Magnetic energy
  • Electrostatic energy
  • Nuclear energy
• Energy transfer


  1. Mechanical

  2. Electrical

  3. Heating

  4. Radiation (light or sound waves)
• System


  Collection of matter
• Open system


  Can exchange energy with the outside world
• Closed system


  Separate from the outside world, neither matter nor energy can enter or leave
• Work done


  Energy transferred
• Types of work done


  • Mechanical
  • Electrical
• Conservation of energy law


  Energy cannot be created or destroyed. It can only be transferred from one form to another.
• Coal fire


  • Coal has a large store of chemical energy (energy within chemical bonds)
  • When coal is burned the chemical energy is transferred by heating to the thermal energy store of the coal
  • Hot coals and flames transfer energy to the surroundings by heating and radiation
• Car braking


  • The moving car has kinetic energy
  • The brakes mechanically do work on the car to slow it down
  • The kinetic energy of the car decreases and the thermal energy store of the brakes increases
• Archer firing a bow and arrow


  • As the string of the bow is pulled back chemical energy in the archers muscles is transferred mechanically to the elastic potential of the bow
  • When the archer releases the string of the bow, the elastic potential energy of the string is transferred mechanically to the kinetic energy store of the arrow
• Kinetic energy


  The energy that an object possesses due to its motion
• Kinetic energy


  • Depends on an object's speed
  • Depends on an object's mass
• Faster an object is moving


  More kinetic energy it will have
• More mass an object has


  More kinetic energy it will have
• Calculating kinetic energy


  1. Use the equation: E_k = 1/2 m v^2

  2. E_k = kinetic energy

  3. m = mass (in kg)

  4. v = velocity (in m/s)
• Particle


  • Mass = 0.0001 kg
  • Speed = 4,000 m/s
  • Kinetic energy = 800 J (or 0.8 kJ)
• Even though the particle was traveling much faster, it had less kinetic energy because its mass was much lower
• Gravity


  A force of attraction between two objects, with the size of the force depending on the mass of the objects and the distance between them
• For small objects like apples or buildings, the gravitational force of attraction is tiny as they have relatively low masses
• For very large objects that are far away like Jupiter, the gravitational force is also tiny due to the large distance
• For very large objects that are close by, such as the Earth or the Moon, gravity is felt more strongly and has a big influence on nearby objects
• Gravitational field


  The field of influence around an object
• Gravitational field strength


  The strength of the gravitational field, denoted by the letter g
• The gravitational field strength on Earth is around 9.8 Newtons per kilogram
• The gravitational field strength on the Moon is 1.6 Newtons per kilogram, as the Moon is much smaller than the Earth
• Weight


  The force of attraction experienced by an object in a gravitational field
• Calculating weight


  Mass x Gravitational field strength
• Weight and mass are different in physics, where mass is an intrinsic property of an object and weight is the force acting on it in a gravitational field
• Gravitational potential energy


  The energy an object has due to its position in a gravitational field
• Calculating gravitational potential energy


  Mass x Gravitational field strength x Height
• Energy can be stored in different forms and it can be transformed from one form to another
• Transfer between kinetic energy (KE) and gravitational potential energy (GPE)


  1. As an object rises, KE is converted to GPE

  2. As an object falls, GPE is converted to KE
• KE lost


  GPE gained
• KE gained


  GPE lost
• Internal energy


  The total energy that's stored by the particles making up a substance or system
• Components of internal energy


  • Potential energy stores
  • Kinetic energy stores
• Potential energy stores (like gravitational and elastic potential) are not really related to temperature
• Kinetic energy


  The movement energy of the particles