What is wind?

As the heat energy of the sun warms the air around the earth, the air expands and rises. As it rises, the air cools and becomes heavier. The cooler air moves down and under warm air. This moving air is called wind.

When wind moves gently, it is called a breeze. It can blow harder too. When the winds are very strong they can become gales and storms. Very strong winds can become hurricanes, typhoons, cyclones and tornadoes.

These can cause floods and other disasters.

Measuring the wind

The Beaufort Wind Scale

This is one way that the strength of the wind is measured. The scale is named after Sir Francis Beaufort, who developed it in 1805 for use by sailors.

You can use the Beaufort scale to measure the force of the wind by looking at the effects of the wind on things around you.

Force 0

  • Calm: 0 km per hour
  • Smoke rises vertically

Force 1

  • Light air: 1-5 km per hour  
  • Smoke blown by wind

Force 2

  • Light breeze: 6-11 km per hour  
  • Leaves rustle, you feel the wind on your face

Force 3

  • Gentle breeze: 12-19 km per hour  
  • Leaves and twigs on trees moving constantly. Flags flutter

Force 4

  • Moderate breeze: 20-30 km per hour  
  • Wind raise dust and fallen leaves. Paper blows around. Small tree branches sway

Force 5

  • Fresh breeze: 31-39 km per hour  
  • Small trees begin to sway

Force 6

  • Strong breeze: 40-50 km per hour  
  • Large branches sway. Umbrellas hard to hold, blown inside out

Force 7

  • Near gale: 51-61 km per hour  
  • Whole trees sway. You can feel the wind pushing you

Force 8

  • Gale: 62-74 km per hour  
  • Difficult to walk in the wind. Twigs and small branches broken off trees

Force 9

  • Strong gale: 75-87 km per hour  
  • Tiles blown off roofs, large tree branches blown down

Force 10

  • Storm: 88-102 km per hour  
  • Damage to houses. Whole trees broken or blown over

Force 11

  • Violent storm: 102-116 km per hour  
  • Serious damage to buildings, trees uprooted

Force 12

  • Cyclone: 117-132 km per hour  
  • Widespread and very severe damage
Sir Francis Beaufort invented a way of measuring the strength of  wind

Sir Francis Beaufort invented a way of measuring the strength of  wind

Yachts are moved by the energy of the wind. Yachts are sailed for recreation and leisure. Getty Images

Yachts are moved by the energy of the wind. Yachts are sailed for recreation and leisure. Getty Images

Using the power of the wind

Humans have used the wind for centuries. 

We still use the energy of the wind for leisure and industry: winds move boats and propel hang gliders, parasails and hot air balloons. Wind energy is used to generate electricity, pump water, grind grain and dry the washing. 

Wind energy becomes electrical energy

A wind turbine is made up of two or three propeller-like blades called the rotor. The rotor is attached to the top of a tall tower. As the wind blows it spins the rotor. As the rotor spins the energy of the movement of the propellers gives power to a generator. There are some magnets and a lot of copper wire inside the generator that make electricity. 

Winds are stronger higher up off the ground, so wind turbine towers are about 30 metres tall to allow the rotor to catch more wind energy. The turbines are built with a device that turns the rotor so that it always faces into the wind. Just one wind turbine can generate enough electricity for a single house, or the electrical energy to pump water, or to power a mill which grinds grain. The electrical energy can also be stored in batteries. Or it is  sent to cables that carry the electricity to our houses and to factories where it powers machines.

Wind turbines are pollution free © Getty Images

Wind turbines are pollution free © Getty Images

Wind farms

Wind farms are places where many wind turbines are clustered together. They are built in places where it is nearly always windy. The electricity that is generated at a wind farm is sold to electricity companies that provide the electricity to people living in cities and towns. 

What are the advantages of wind turbines?

They are pollution free.

The energy they generate is renewable. This means that as long as the winds blow there is power to turn the blades of the rotor. (Another form of renewable energy comes from the Sun. Energy from the Sun is called solar energy)

Using wind energy means that less fossil fuel (coal and oil) needs to be burned to make electricity. Burning fossil fuel pollutes the atmosphere and adds greenhouse gases to it. This pollution is a cause of global warming.

What are the disadvantages of wind turbines?

  • Some people don't like the look of the turbines. They say that they spoil the look of the natural environment.

  • Wind turbines make some noise.

  • Turbines kill birds that fly into them. However collisions are rare and there are reports from Denmark saying that some falcons had built nests on the top of turbine towers. To protect birds however, it is important that wind farms be built away from bird sanctuaries and from the pathways of migratory birds. (Migratory birds are those that fly from cold places in winter to warmer parts of the world)

Watch this video and see animations that show how a wind turbines work: