http://u.nu/8ub23

or: http://u.nu/4vb23

Principle of Operation of Vehicles in the Air

http://u.nu/34a23

or: http://u.nu/54a23

Hot-Air Balloons

The upward motion of a hot-air balloon is based on the principle of Archimedes. The upthrust that acts on the hot-air balloons is equal to the weight of the air displaced. In the hot-air balloon, a gas burner is used to heat the air. The density of hot air and helium gas is less than the density of air. Hence the upthrust or the weight of air displaced is larger than the weight of the hot-air balloon.

http://u.nu/46a23

or: http://u.nu/65a23

The density of air decreases with height. When the hot-air balloon rises, the upthrust will decrease. The hot-air balloon will float in the atmosphere when the upthrust is balanced by its weight. The direction and forward motion of the hot-air balloon depends on the direction of wind. The descent of the hot-air balloon is controlled by reducing the amount of hot air.

http://u.nu/9sb23

or: http://u.nu/4tb23

Airships

The upward motion of an airship is based on the principle of Archimedes. A large amount of air is pushed backwards very quickly by the airship’s propellers, creating a large backward momentum. A forward momentum that is of equal magnitude to the backward momentum is produced, causing the airship to move forward.

http://u.nu/67a23

or: http://u.nu/77a23

The density of air decreases with height. When the airship rises, the upthrust will decrease. The airship will float in the atmosphere when the upthrust is balanced by its weight. The descent of the airship is controlled by releasing the helium gas inside it and its direction is controlled by a rudder.

http://u.nu/58a23

or: http://u.nu/88a23

Helicopters

A helicopter does not need a runway because it can take off or land vertically. The rotation of the rotor or propeller blades at high speed will create an upthrust or lift. The helicopter will take off if the lift is greater than its weight. The forward or backward motion of the helicopter is controlled by the slope of its blades. The helicopter will hover if the blades are horizontal. The rotation of the rotor also produces a twist or force that pushes the helicopter sideways. This is overcome by rotating a tail rotor so that a force is produced to balance the sideways force.

http://u.nu/79a23

or: http://u.nu/69a23

Airplanes

An airplane needs a long runway to take off or to land. The upward motion of the airplane is due to the lift produced when the airplane cuts through the air at high speed. The airplane will move upwards of the lift is greater than the weight of the airplane. The forward thrust is produced by jet engine. The hot gases that are expelled continuously at its rear with high speed produce the thrust. When an airplane flies at a uniform velocity; a) the lift is equal to the weight of the airplane b) the engine thrust is equal to the air resistance (drag).

http://u.nu/7aa23

or: http://u.nu/8aa23

Jet Engines

Air from the atmosphere is sucked into the front of the engine by large spinning fan. The air is compressed to a very high temperature and pressure by a compressor fan and is pushed into a combustion chamber. In the combustion chamber, combustion fuels such as naphtha, kerosene or paraffin are sprayed into the air and burned.

http://u.nu/7cb23

or: http://u.nu/9cb23

The hot gases from the burning of fuel and air expand and force themselves through a turbine and out through the exhaust nozzle at high speed. The turbine rotated by the hot gases is connected to the compressor. The backward momentum of the hot gases produces a forward momentum on the engine. This produces a thrust that enables the jet engine to move forward.

http://u.nu/9ba23

or: http://u.nu/7ba23

Rockets

A rocket is used for space exploration and launching satellites in orbits around the earth. A typical liquid fuel rocket engine is separate tanks containing liquid oxygen as there is very little oxygen or atmosphere at great height. The mixture of hydrogen gas and oxygen is burnt in a combustion chamber. The exhaust gases are discharged downwards at high speed. The exhaust gases have a large momentum. According to the principle of Conservation of momentum, an upward momentum of equal magnitude acts on the body of the combustion chamber. This creates an upthrust that launches the rocket.

http://u.nu/4mb23

or: http://u.nu/5mb23

Bernoulli’s Principle

1. The pressure in a moving fluid depends on the velocity of the fluid.
2.  Bernoulli’s principle states that in a steady flow of fluid, the pressure in the fluid is low when the velocity of the fluid is low when the velocity of the fluid is high. Similarly the pressure in the fluid is high when the velocity of the fluid is low.

• When air flows from the nozzle of an air pump across the top surface of a paper, the free end of the paper is pushed upwards.
• The pressure around the area of air flow is lower. The pressure around of the still air beneath the paper is higher. The difference in pressure produces a net force that lifts up the paper.

http://u.nu/5jb23

or: http://u.nu/6jb23

• When air is blown vigorously between two sheets of paper held vertically, the two sheets of paper are pressed together by the air outside.

• The high velocity of air creates a low pressure area between the two sheets of paper. The air outside the two sheets of paper which is at a lower velocity will press the two sheets of paper together because it has a higher pressure.

http://u.nu/8ea23

or: http://u.nu/2fa23ch,

• When a jet of air flows through the inverted filter funnel, the table tennis ball d oes not drop but is suspended beneath the funnel.
• The air flows around the table tennis ball at high speed and creates a region of low pressure. The higher atmospheric pressure beneath the ball produces a net upwards force which is larger than the weight of the table tennis ball. This causes the table tennis ball not to drop.

http://u.nu/6pb23

or: http://u.nu/8pb23

Application of Bernoulli’s Principle in Air Flight

The lift or upthrust that enables an airplane to fly is caused by the flow of air around its wings. The wings of an airplane are in the form of an aerofoil. Its top surface is curved while the bottom is flat. As the plane cuts through the air, the air that flows over the top of its wings has to travel a greater distance than the air flowing underneath its wings. So the air has to travel faster over the top than the bottom. Hence the air pressure on the top and bottom of the wings produces an upward force or lift that pushes the wings upwards.

http://u.nu/9qb23

or: http://u.nu/3rb23

Science, Technology and Society

Meteorological balloons are filled with hydrogen, helium or coal gas. They are released into the upper atmosphere to measure and record information about temperature, wind, humidity and pressure.