EnergyEnergy

Definition:Definition: In general, the word In general, the word energyenergy refers refers to a concept that can be defined to a concept that can be defined

as "as "the potential for causing the potential for causing changeschanges", and therefore one can ", and therefore one can say that energy is the cause of say that energy is the cause of

any change any change

FormsForms of Energy 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.

KINETIC ENERGYKINETIC ENERGY

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

Electrical EnergyElectrical 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.

Radiant EnergyRadiant 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.

Thermal EnergyThermal Energy

• Thermal energy or heat, is the internal energy in substances

• Geothermal energy is an example of thermal energy.

Motion EnergyMotion 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 Newton’s Laws of Motion F = M*a

POTENTIAL ENERGYPOTENTIAL ENERGY

• Potential energy is stored energy and the energy of position––gravitational energy. There are several forms of potential energy.

Chemical Energy.

Stored Mechanical Energy

Nuclear Energy.

Gravitational Energy

Chemical EnergyChemical 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.

Stored Mechanical EnergyStored 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

Nuclear EnergyNuclear 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.

Nuclear EnergyNuclear 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.

Gravitational EnergyGravitational 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.

Conservation of energyConservation of energy

• The law of conservation of energy says that energy is neither created nor destroyed. When we use energy, it doesn’t disappear. We change it from one form of energy into another.

Conservation of energyConservation 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.

Energy Units and ConversionsEnergy 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 = 1N*1m 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

Energy Units and ConversionsEnergy 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

Energy Units and ConversionsEnergy 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

Mechanical powerMechanical 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

Exercices 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 = F*D

ExercicesExercices

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.

Exercices 2Exercices 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

Exercices 3Exercices 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

Exercices 4Exercices 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?