PHYSICS HOLIDAYHOMEWORK !!!

Presented By:Divye Bhutani

Principles OF Physics Involved In :-

Flying Of an Airplane

Working Of a Vacuum Cleaner

Working Of Radio

It is easy to take the physics of flight for granted, as well as the ways in which we exploit them to achieve flight. We often glimpse a plane in the sky with no greater understanding of the principles involved than a caveman.

How do these heavy machines take to the air? To answer that question, we have to enter the world of fluid mechanics.

Physicists classify both liquids and gases as fluids, based on how they flow. The core of the matter is this: Even a clear sky isn't empty. Our atmosphere is a massive fluid layer, and the right application of physics makes it possible for humans to traverse it.

Steel ships can float and even very heavy airplanes can fly, but to achieve flight, you have to exploit the four basic aerodynamic forces: LIFT, WEIGHT, THRUST and DRAG. You can think of them as four arms holding the plane in the air, each pushing from a different direction

First, let's examine thrust and drag. Thrust, whether caused by a propeller or a jet engine, is the aerodynamic force that pushes or pulls the airplane forward through space.

For flight to take place, thrust must be equal to or greater than the drag. If, for any reason, the amount of drag becomes larger than the amount of thrust, the plane will slow down. If the thrust is increased so that it's greater than the drag, the plane will speed up.

The opposing aerodynamic force is drag, or the friction that resists the motion of an object moving through a fluid (or immobile in a moving fluid, as occurs when you fly a kite).

If you stick your hand out of a car window while moving, you'll experience a very simple demonstration of drag at work. The amount of drag that your hand creates depends on a few factors, such as the size of your hand, the speed of the car and the density of the air. If you were to slow down, you would notice that the drag on your hand would decrease.

Weight's opposing force is lift, which holds an airplane in the air. This feat is accomplished through the use of a wing, also known as an airfoil. Like drag, lift can exist only in the presence of a moving fluid. It doesn't matter if the object is stationary and the fluid is moving (as with a kite on a windy day), or if the fluid is still and the object is moving through it. What really matters is the relative difference in speeds between the object and the fluid.

As for the actual mechanics of lift, the force occurs when a moving fluid is deflected by a solid object. The wing splits the airflow in two directions: up and over the wing and down along the underside of

the wing.

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The wing is shaped and tilted so that the air moving over it travels faster than the air moving underneath. When moving air flows over an object and encounters an obstacle (such as a bump or a sudden increase in wing angle), its path narrows and the flow speeds up as all the molecules rush though. Once past the obstacle, the path widens and the flow slows down again. If you've ever pinched a water hose, you've observed this very principle in action. By pinching the hose, you narrow the path of the fluid flow, which speeds up the molecules. Remove the pressure and the water flow returns to its previous state.

As air speeds up, its pressure drops. So the faster-moving air moving over the wing exerts less pressure on it than the slower air moving underneath the wing. The result is an upward push of lift. In the field of fluid dynamics, this is

known as Bernoulli's principle.

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WORKING OF A VACUUM CLEANER

When you sip soda through a straw, you are utilizing the simplest of all suction mechanisms. Sucking the soda up causes a pressure drop between the bottom of the straw and the top of the straw. With greater fluid pressure at the bottom than the top, the soda is pushed up to your mouth.

This is the same basic mechanism at work in a vacuum cleaner, though the execution is a bit more complicated. In this article, we'll look inside a vacuum cleaner to find out how it puts suction to work when cleaning up the dust and debris in your house. As we'll see, the standard vacuum cleaner design is exceedingly simple, but it relies on a host of physical principles to clean effectively.

1. The electric current operates the motor. The motor is attached to the fan, which has angled blades.2. As the fan blades turn, they force air forward, toward the exhaust port. 3.When air particles are driven forward, the

density of particles (and therefore the air pressure) increases in front of the fan and decreases behind the fan.

4.This pressure drop behind the fan is just like the pressure drop in the straw when you sip from your drink. The pressure level in the area behind the fan drops below the pressure level outside the vacuum cleaner (the ambient air pressure). This creates suction, a partial vacuum, inside the vacuum cleaner. The ambient air pushes itself into the vacuum cleaner through the intake port because the air pressure inside the vacuum cleaner is lower than the pressure outside.

5. As long as the fan is running and the passageway through the vacuum cleaner remains open, there is a constant stream of air moving through the intake port and out the exhaust port. But how does a flowing stream of air collect the dirt and debris from your carpet? The key principle is

friction.

The moving air particles rub against any loose dust or debris as they move, and if the debris is light enough and the suction is strong enough, the friction carries the material through the inside of the vacuum cleaner. This is the same principle that causes leaves and other debris to float down a stream.

As the dirt-filled air makes its way to the exhaust port, it passes through the vacuum-cleaner bag. These bags are made of porous

woven material (typically cloth or paper), which acts as an air filter. The tiny holes in the bag are large enough to let air particles pass by, but too small for most dirt particles to fit through. Thus, when the air current streams into the bag, all the air moves on through the material, but the dirt and debris collect in the bag.

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WORKING OF A RADIO

A radio wave is an electromagnetic wave

propagated by an antenna. Radio waves

have different frequencies. The

listener can tune the radio receiver to a

specific frequency to catch a specific radio

signal. For example, all FM radio stations

transmit in a band of frequencies between 88 megahertz (millions of cycles per second) and

108 megahertz, and any listener who tunes his radio receiver to a frequency falling in

this range would have access to that specific

FM radio station's programs.

Every radio setup consists of two parts, the Transmitter and the Receiver. The transmitter receives the message, encodes it onto a sine wave (a continuously varying electromagnetic wave) and transmits it with radio waves. The receiver receives the radio waves and decodes the message from the sine wave it received.

The transmitter and the receiver use antennas to radiate and capture radio signals. The function of the antenna in a radio transmitter is to send radio waves into space, and in a radio receiver, it is to capture the transmitter's power to the maximum extent and route it to the tuner. The size of the antenna depends on the frequency of the signal to be transmitted or received.

A radio station transmits the sine waves, with information (programs) encoded on them, into space with help of an antenna. These sine waves are captured by antenna at the receiving station (radio set). The sine waves themselves do not contain any information and are modulated so as to hold information.

Normally, sine waves are modulated in three ways: • Pulse Modulation (PM): In PM, the sine wave is turned on and off at specific intervals. This is an easy way of sending coded messages. Usage of PM is comparatively less. • Amplitude Modulation (AM): In AM, the amplitude of the sine waves (its peak to peak voltage) differs. AM is the most commonly used mode across the world. • Frequency Modulation: In FM, the transmitter's sine wave frequency changes very slightly, based on the information signal. FM is largely immune to static (not useful or empty transmissions), which enhances the effectiveness of transmissions.

The sine waves with encoded messages are captured by antenna and sent to the tuner in the receiving station. The tuner's function is to separate one from the other, the thousands of sine waves received by the antenna. Tuners use the resonance principle, i.e. they resonate and amplify at one sine wave frequency, ignoring all other sine wave frequencies.

They thus enable radio to receive only one sine wave frequency.

The decoding of the information on sine waves in that particular frequency is done with the help of a demodulator or detector in the radio (detector defers from one radio type to the another). The radio amplifies this decoded information and sends it to the speakers (or headphone), from where the listener listens to the information.

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Presented By:Divye Bhutani