Energy

1
Energy

• Definition
• In general, the word energy refers to a concept
  that can be defined as "the potential for
  causing changes", and therefore one can say that
  energy is the cause of any change

2
Forms of Energy

• Energy is found in different forms, such as
  light, heat, sound and motion. There are many
  forms of energy, but they can all be put into two
  categories kinetic and potential.

3
KINETIC ENERGY

• Kinetic energy is motion of waves, electrons,
  atoms, molecules, substances, and objects.

4
Electrical Energy

• Is the movement of electrical charges. Everything
  is made of tiny particles called atoms. Atoms are
  made of even smaller particles called electrons,
  protons, and neutrons. Applying a force can make
  some of the electrons move. Electrical charges
  moving through a wire is called electricity.

5
Radiant Energy

• Is electromagnetic energy that travels in the
  space. Radiant energy includes visible light,
  x-rays, radio waves and gamma rays.
• Solar energy is an example of radiant energy.

6
Thermal Energy

• Thermal energy or heat, is the internal energy
  in substances
• Geothermal energy is an example of thermal energy.

7
Motion Energy

• Is the movement of objects and substances from
  one place to another.. Wind is an example of
  motion energy
• Objects and substances move when a force is
  applied according to Newtons Laws of Motion F
  Ma

8
POTENTIAL ENERGY

• Potential energy is stored energy and the energy
  of positiongravitational energy. There are
  several forms of potential energy.
• Chemical Energy.
• Stored Mechanical Energy
• Nuclear Energy.
• Gravitational Energy

9
Chemical Energy

• Is energy stored in the bonds of atoms and
  molecules. It is the energy that holds these
  particles together. Biomass, petroleum, natural
  gas, and propane are examples of stored chemical
  energy.

10
Stored Mechanical Energy

• Is energy stored in objects by the application of
  a force. Compressed springs and stretched rubber
  bands are examples of stored mechanical energy

11
Nuclear Energy

• Is energy stored in the nucleus of an atom
• The energy that holds the nucleus together can be
  released when the nuclei is split apart. Nuclear
  power plants split the nuclei of uranium atoms in
  a process called fission.

12
Nuclear Energy

• nuclear fusion is the process by which multiple
  nuclei join together. Later we have a heavier
  nucleus and the release of energy
• Scientists are working on creating fusion energy,
  so that someday there might be fusion power
  plants.

13
Gravitational Energy

• Is the energy of position or place.
• A rock resting at the top of a hill contains
  gravitational potential energy.
• Hydropower, such as water in a reservoir behind a
  dam, is an example of gravitational potential
  energy.

14
Conservation of energy

• The law of conservation of energy says that
  energy is neither created nor destroyed. When we
  use energy, it doesnt disappear. We change it
  from one form of energy into another.

15
Conservation of energy

• Energy cannot be created or destroyed but can
  only be transferred from one body to another or
  change from one form to another.
• A car engine burns gasoline, converting the
  chemical energy in gasoline into mechanical
  energy. Solar cells change radiant energy into
  electrical energy.

16
Energy Units and Conversions

• In the International System, energy is measured
  in joules
• Joule (J) is the unit of energy, equal to the
  force of one Newton acting through one meter.
• 1J 1N1m There is another energy units, the
  calorie
• 1 calorie of heat is the amount needed to raise 1
  gram of water 1 degree Centigrade.
• 1 calorie (cal) 4.184 J

17
Energy Units and Conversions

• Calculate how many calories are
• a) 2005 joules
• b) 3566 joules
• Calculate how many joules are
• A) 34545 calories
• B) 5664 calories

18
Energy Units and Conversions

• Find the work (energy) done when a horse exert a
  horizontal force of 400 N on a cart and pulls it
  20 m in the direction of the force

19
Mechanical power

• Power is the rate at which work is done.
• Power work done / time taken.
• The measured of power is watt ( W)
• So if time is measured in seconds and work in
  Jules
• 1W 1J/1s

20
Exercices

• Exercices 1º
• A car engine provides a forward force of 1000 N.
  If the car is travelling at 20 m s-1, what power
  is developed?
• Remember that
• work Force multiplied by distance or
• W FD

21
Exercices

• Solution
• In 1 s, the car travels 20 m. Hence we can
  calculate
• Work done in 1 s force distance 1000 N 20
  m 20 000 J 20 kJ
• Power work done / time taken 20 kJ / 1 s 20
  kW.

22
Exercices 2

• A man raises a object of mass 40 kg through a
  vertical height of 20 m in 4 seconds. Find the
  power.
• Note The potential energy is measured by the
  following equation
• Pe m x g x h
• Where
• M mass , g 9,8 , h height
• Solution 1960 W

23
Exercices 3

• A women run up a flight of 120 stairs in 30
  seconds. If the height of each stair is 15 cm,
  find the power
• Solution 294 watts

24
Exercices 4

• 4.1) A 100 watt electric heater is used to heat
  water and bring it to the boil. If 5000 j are
  needed to bring the water to the boil, for how
  long is the heater operating?
• 4.2) How much energy is given out by a 60W bulb
  the is running 5 hours?