Download ENERGY +Energy is the ability a material system has to produce

ENERGY
+Energy is the ability a material system has to produce changes in another material system or on itself.
+Energy has two main characteristics:
 It can appear in different forms and it can change its form into any other one.

When it transforms, its value remains the same on every natural phenomenon.
Law of conservation of Energy
+In any chemical or physical change, energy can be changed from one form to another, but it cannot be
created or destroyed. The total amount of energy stays the same. This
is also called First law of thermodynamics. When two systems interact,
the amount of energy one losses is equal to the amount of energy the
other gains.
Formula of increasing energy.
∆E = 0
increasing energy = 0
+The I.S (International System) of units of energy is the Joules (J). Another old unit exists, called calorie,
even though nowadays is only used in nutrition and food labeling.
1 calorie = 4,184 Joules.
+When a system interacts with other system, it experiences a change and both systems exchange
energy. During this period, energy becomes “energy in transit”, and it can be different: Heat and Work.
This way, it is impossible to store Heat and Work. You store energy in some form.
 Heat. When two bodies are at different temperatures, the system with the higher temperature
transfers its Energy (through Heat) to the other. Then both bodies reach the same T and are in
Thermal equilibrium.
 Work. When two bodies exchange Energy through some kind of force. Usually, it involves
movement.
Types of energy
+Mechanical energy (Em) is the energy a body stores. It is calculated by adding the Kinetic energy (Ek)
plus the gravitatorial Potential energy (Ep).
Law of Mechanical Energy
Em = Ek + Ep


mechanical energy equals kinetic energy plus potential energy.
Kinetic Energy (Ek): Is the energy a body has because it’s moving at a certain speed.
Potential Energy (Ep): Is the energy a body has due to the effect of gravity.
Formula of Kinetic and Potential Energy
Ek = 1/2mv₂ Kinetic energy equals half the mass by the speed to two.
Ep = mgh potential energy equals the mass by the gravity by the height.
+If we remember the law of conservation of energy, the energy of a body never changes in, for
example, a fall. In this way, the Em at the beginning and the Em at the end will be the same. In a fall, a
body can change its Ep into Ek and vice versa.
Laws of the mechanical energy
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∆Em = 0
Increasing in mechanical energy equals “0”.
Em (final) -Em (initial) = 0 The final mechanical energy subtracted by the initial one equals 0.
+Electrical energy (Ee) is the energy coming from an electric current, which is an organized movement
of electrons or particles with an electric charge. It can only happen in materials that allow this
movement. This energy cannot be stores so it must be consumed once it is produced. It is very comfort.
+Chemical energy is the energy from chemical bonds which keep atoms together. When we break these
bonds, we obtain this energy. It is present on chemical reactions and it can appear in form of heat or
light. A common chemical reaction is combustion, the oldest form of energy. This energy is also present
in metabolism. This energy causes pollution, and this causes CO2 (Greenhouse effect) and SO2 (Acid
rain).
+Nuclear energy is the energy obtained when we change an atom’s nucleus. There are two types:
 Fission. When the nucleus of a big atom is broken and two smaller ones are obtained. This
produces Uranium and Plutonium. This produces toxic wastes that can produce mutations on
living beings.
 Fusion. When two small nucleus are joined together (like the energy produced in the Sun).
+This model of consuming energy is not sustainable, and our future generations will suffer the
consequences. E should be used in a fairer way for benefits of the future generations. There are two
main sources of E:
 Nonrenewable resources of energy are those that are found in a limited quantity like fossil
fuels (petroleum, gas) and nuclear fuels.
 Renewable resources are those that can be found in unlimited quantity, and can be consumed
at the same time Nature replaces them.
 Wind power
 Hydraulic energy
 Hydroelectric energy
 Geothermal energy
Work
+When a force moves a body we say it carries out force on it. This is called Work. Work is represented
with a W, and its unit is the Joule.
Formula of the Work
W = Fd Work equals the force by the distance.
+We can redefine E. E is the ability a material system has to do Work.
Machines
 Pulley. Permits a change in the direction of
the force is been applied.
 Slope. Helps us with the weight of an
object we want to move at a certain
height.
 Lever. Bar that is supported in the middle
and when we apply force on one end, the
other one lifts.
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+Machines cannot transform all the E they consume into W (useful E), because part of this energy is lost
with friction between pieces or with the floor.
+Output of a machine (R) is the percentage of consumed energy divided by the produced x100.
 Wind turbine 60 %
 Solar cell 15 %
 Combustion engine 30 %
 Electric motor 80 %
 Water turbine 90 %
 Incandescent light bulb 10 %
 Fluorescent lamp 30 %
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