When we throw a stone into a pool of water circular waves from and move outward. Waves will also travel along a cord or rope that is streched out straight on a table and if we vibrate one end back and forth. Water waves on a cord, are two common examples of wave motion. In this Chapter we will concentrate on Mechanical Waves — Waves that travel in a material medium.
All types of wavs have as their source a vibration. Water waves for example move with a recognisable velocity, but each particle of the water itslef merely osillates about an equillibrium position. This is easily seen when we observe leaves on a pond as waves pass by. The leaves are carried forward by the waves, but simpily move up and down about an equillibrium point because this is the motion of the water itself. This is a general feature of waves: Waves can move over large distances but the medium (e.g the water or the cord) itself has only a limited movement. A wave consists of oscillations that move without carrying matter with them. Such up-and-down movement or vibration or oscillation of the medium (e.g Water) which causes waves is an example of wave motion.
A Wave Motion is a Process of transferring a disturbance (in form of Kinetic energy) from one point to another in a medium without any transfer of particles. A Wave is a disturbance which travels through a medium without transferring energy from one point to another without causing any permanent displacement of the medium.
Not all waves, however, require a material medium for their propagation. Mechanical Waves are those waves that require a material medium for their propagation. Examples of such waves are Water Waves, sound waves, waves on a rope or string.
Electromagnetic waves are waves that do not require a material medium for propagation. Examples are ligh waves, radio waves, X-rays and gamma Waves.
Production of Mechanical Waves: The Motion of any Material object may be considered as a source of waves.
Waves of a String
1. Hold one end of a tight string or ropes as shown in figure. The other end of the ropw is tied to a nail on a Wall. Tie some ribbons all along the rope.
2. Move the end of the rope in your hand up and down rapidly.
3. Observe a set of waves travelling along the rope. Obeserve the movements of the ribbons. As we move the end of the rope, a pulse will be sent down the rope just like Figure, A repeating set of pulses sent down the rope is called a wave.
The Waves have been generated by the vibration of the particles of the rope about their mena position of rest. The ribbons are also observed to move up and down while the wave travels along the rope from the hand to the nail on the wall.
Waves in Slinky Spring.
1. Obtain a long loose spring called a Slinky spring
2. Support the Slinky spring horizontally at one end and move the other end up and down in a vertical direction.
3. Observe the wave as it travels along the spring
4. With the aid of a long pencil compress the free end of the Slinky Spring as shown in Figure
It will be observed that the compressed part (compression) travels along the spring while one particular turn, indicated by the paper makerm only vibrates back and forth. Every turn of the slinky spring vibrates in the direction in which the compression travels. Thus the wave generated by the compression of the slinky spring travels parallel to the direction of the compression or the disturbance producing the wave.
a. Position of coils befor compression. The arrows shows the rest position of the turn indicated by the paper marker. b. The coil is compressed with a pencil. here the compression has not reached the turn indicated by the turn indicated by the marker. norice that the turns on the left of the pencil are further apart than in a. c. the compression has travelled to the right. Notice that the marked turn has also travelled in the same direction. After Reflection at the wall both the compression andthe marked turn tracelin the opposite direction i.e to the left. The marked turn is now back in its rest position. the marked turn together with the other turns of the coil have merely vibrated back and forth while a wave travelled along the spring.
Water waves in ripple Tank.
If a stone is dropped into a pool of water in a pond or stream, ripples are seen to form, grow quickly and die away. The falling stone creates a disturbance of the calm water surface and produces ripples. Such ripples are called pulses. A Pulse consists of a single crest, A Pulse is a sudden increase in Magnitude of a physical quantitym shortly followed by a rapid decrease.
We can produce continous water ripples or pulses in form a water wave by disturbing the water surface continously e.g by throwing in stones at regular intercals, In the laboratory water waves can be produced and studied in a ripple tank.