The weather

A force is anything which is capable of changing the state of motion or rest of a body, or deforming it.
The effects produced by forces on bodies are not always the same and depend on various factors such as the intensity of the force, the duration of that force and the characteristics of the body which receives it.

When we apply a force to a body, the following phenomena can happen:

The body starts to move.

The direction or type of motion of the body is changed.

Forces can cause deformation in bodies. According to how bodies are deformed when a force is applied to them, they are classified into:

These recover their original shape when the force is removed.

These adopt a new shape and do not recover their initial shape when the force is removed.

These break if the applied force is intense enough.

When bodies, which are in contact with each other, move or try to move over each other, their surfaces rub

rub (v):
to apply pressure with movement

• Roughness of the surfaces: when the supported bodies have the same weight, the rougher the surfaces, the greater the force of friction between them.
• Weight of the supported body: when the surfaces have the same roughness, the greater the weight of the supported body, the greater the force of friction between them.

The force of attraction which is produced between all masses in the Universe is called gravitational force.

This force helps us to understand movement within the Universe: satellites revolve around their planets, planets revolve

Satellite revolving around the Earth

When we weigh things, we usually confuse two different magnitudes: mass and weight.

Mass (m) is the amount of matter in a body.

Weight (W) is the force with which the Earth attracts a body.

The weight of a body is calculated using the equation:
                                                         W = m · g

Electrical charge is a property of matter which can be positive or negative. Some bodies have positive charges, some have negative ones, while some are equally positively and negatively charged, and therefore their charge is neutral. Depending on their charge, bodies behave in different ways:

• When two bodies have the same charge (positive or negative), they repel.
• When two bodies have different charges (positive or negative), they attract.

Conducting materials allow electrical current to flow.

Insulating materials do not allow electrical current to flow. For this reason, cables are covered in plastic.

Some materials have magnetic properties. In other words, they can attract other metallic objects. Magnets have two areas, the north pole and the south pole. If we bring together two similar poles, they repel. If they are different, they attract.
Electromagnetism is the relationship between magnetism and electricity.

Energy has the capacity to produce changes in matter, such as causing a body to move or change its temperature.

Bodies with kinetic energy are those which are in motion.

Light energy appears in the form of light.

Sound energy is transmitted by bodies when they vibrate through sound waves, for example, the sound of the sea.

Chemical energy is stored in some substances, such as fuels and food.

Electrical energy is transmitted through conducting materials in the form of electrical current.

Thermal energy is that which produces heat.

Energy is found all around us and can appear in different forms: mechanical, thermal, electrical, light, sound or chemical.

Energy cannot be created or destroyed, but only transformed. For example, in a hydroelectric power station, the kinetic energy of water is transformed into electrical energy. When this energy arrives at a house and is used in an oven, it is transformed into thermal energy.
Energy can be stored, for example, in batteries where it is stored as chemical energy.

An energy source is a natural resource from which we can obtain energy. Energy sources can be renewable or non-renewable.

These do not run out. They are renewed in nature faster than they are consumed.

• Solar energy
  Solar panels are used to obtain electricity or heat.
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• Wind or hydraulic energy
  These originate from the movement of air and water respectively. Kinetic energy is transformed into electricity in both cases.
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• Energy from organic material
  Organic waste or wood contain chemical energy which can be transformed into electricity or heat.
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The natural production of these sources is slow and they can run out if they are consumed too quickly.

• Fossil fuels
  Oil, natural gas and coal originate from the decomposition of living beings over millions of years. Their combustion is transformed into electrical energy or heat.
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• Radioactive substances, uranium and plutonium  These contain nuclear energy, which can be transformed into electrical energy.
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Heat is the transfer of thermal energy, passing from one body to another, when these bodies are at different temperatures.
Temperature is a magnitude which measures the degree of movement of the particles in a body.

The International Temperature Scale admits the following units of measurement:

• Degrees Celsius (ºC): the melting point of ice has an assigned value of 0 ºC and the boiling point of water has an assigned value of 100 ºC.
• Kelvin (K): a value of 273.15 K is assigned to the melting point of ice and 373.15 K to the boiling point of water.
                                                               T (K) = 273.15 + t (ºC)
  

When two bodies with different temperatures are brought into contact, heat passes from the body with the highest temperature to the one with the lowest temperature, until both have the same temperature. In other words, they reach thermal equilibrium.

When the temperature of a material changes, the following phenomena can occur:

• Expansion: if the temperature increases, materials increase in size. In other words, they expand.
• Contraction: if the temperature decreases, materials decrease in size. In other words, they contract.

Expansion and contraction affect matter in any state, but not in the same way. Gases expand much more than liquids and solids as their particles are weaker and they can separate more when the temperature increases.

The expansion of liquids is very important for the manufacture