Ensayo

THE NATURE OF WAVES
A wave is a repeating disturbance or movement that transfers energy through matter or space. For example, ocean waves disturb the water and transfer energy through it. During earthquakes, energy is transferred in powerful waves that travel through earth. Light is a type of wave that can travel through empty space to transfer energy from one place to another, such as fromthe sun to earth.

WAVES AND ENERGY
A pebble falls into a pool of water and ripples form. The pebble causes a disturbance that moves outward in the form of a wave. Because it is moving, the falling pebble has energy transfers some of its energy to nearby water molecules, causing them to move. These molecules then pass the energy along to neighboring water molecules, which, in turn, transfer it totheir neighbors. The energy moves farther from the source of the disturbance. What you see is energy traveling in the form of a wave on the surface of the water.

MAKING WAVES
A waves will travel only as long as it has energy to transfer. For example, when you drop a pebble into a puddle, the ripples soon die out and the surface of the water becomes still again.
Suppose you are holding a rope atone end, and you give it a shake. You would create a pulse that would travel along the rope to the other end, and then the rope would be still again as figure 7 shows.
Anything that moves up and down or back and forth in a rhythmic way is vibrating. The vibrating movement of your hand at the end of the rope created the wave. In fact, all waves are produced by something that vibrates.
TYPES OFWAVES
MECHANICAL WAVES need a material medium through which they transfer energy. Some examples of mechanical waves are water waves, sound waves and the waves that travel along a spring or rope. The behavior of most mechanical waves can be readily observed.
ELECTROMAGNETIC WAVES are a large and family of waves. They need no medium through which to travel. Some examples of electromagnetic waves arelight waves, radio waves and x rays. We cannot observe electromagnetic waves directly.
Mechanical waves can be classified by the way in which they displace matter. There are three general types of waves: transverse waves, longitudinal waves, surface wave a transverse wave causes the particles of a medium to vibrate perpendicularly to the direction of the wave itself.
A longitudinal wave causes theparticles of a medium to move parallel to the direction of the wave. Sound wave is an example of a longitudinal wave.
Surface waves have characteristics of both transverse a longitudinal waves. Surface waves cause particles in the medium to move both horizontally and vertically as the wave moves across the surface. Water waves are examples of surface waves.
WAVE SPEED
The speed of a wave depends ofthe medium in which the wave travels. You can calculate the speed of a wave if you know its wavelength and frequency using the equation below.
WAVES AND MATTER imagine that you’re in a boat on a lake, approaching waves bump against your boat, but they don’t carry it along with them as they pass. The boat does move up and down and maybe ever a short distance back and for because the wavestransfer some of their energy to it. However, after the waves have moved on, the boat still in nearly the same place. The waves don’t even carry the water along with them. Only the energy transferred by the waves moves forward. All waves have this property: their transfer without transporting matter form place to place.
THE LAW OF REFLECTION
The normal is a line perpendicular to the reflectingsurface (the barrier) at the point where the incident ray strikes the surface. The angle of incidence is the angle between the normal N and the incident ray. Similarly, the angle of reflection is the angle between the normal N and the reflected ray.
Waves are reflected from a barrier at the same angle at which they approach it. The law of reflection states that the angle of reflection is equal to...