WAVES

The Nature of Waves What is a wave? A wave is a repeating disturbance or movement that transfers energy through matter or space Waves transfer energy not matter. The water waves below are carrying energy but are not moving. Waves can only exist if they have energy to carry them.

Most waves (Mechanical Waves) transfer energy by the vibration of particles in a medium. A Medium is a substance through which a wave can travel (solids, liquids, or gases) (a physical environment in which phenomena occur) When particles vibrate they pass their energy to their neighboring particle, transmitting the energy.

Some waves can transfer energy without going through a medium Some waves can transfer energy without going through a medium. These waves are called Electromagnetic Waves. Examples would be: visible light, microwaves, TV and radio signals, and X rays.

Waves that need a Medium are called Mechanical Waves. Some examples are Slinky waves, water waves, jump rope waves, or sound waves.

There are two types of waves: Transverse Waves and Longitudinal Waves. Transverse means “moving across” and in a transverse wave the particles move across, or perpendicularly to, the direction that the wave is going. To be perpendicular to means to be at right angles to.

A Longitudinal Wave is one in which the particles of the medium vibrate parallel to the direction of wave motion. If you push on the end of a slinky, the coils of the spring crowd together. A part of the longitudinal wave where the particles are crowded together is called compression. The part where the particles are spread apart is a rarefaction.

Parts of a wave Transverse Wave

Properties Common to all Waves Amplitude – the maximum distance that the particles of a wave’s medium vibrate from their rest position. - a measure of the energy carried by a wave. - simple put it is how big the wave gets The amplitude of a longitudinal wave is related to how tightly the medium is pushed together at the compressions. Higher amplitude waves have tighter coils.

The shorter the wavelength, the more energy. Wavelength – the distance between any two crests or compressions next to each other in a wave. The shorter the wavelength, the more energy. Frequency – The number of waves produced in a given amount of time. It is usually expressed in hertz (Hz). For waves, one hertz equals one wave per second (1Hz=1/s) Period – the amount of time it takes one wave- length to pass a point. If frequency increases, the period decreases.

Wave Speed The speed of a wave depends on the medium it is traveling through. Sound waves usually travel faster in liquids and solids than they do in gases. Light waves travel more slowly in liquids and solids than they do in gases or in empty space. Also, sound waves usually travel faster in warmer material than cool. You can calculate the wave speed of a wave as follows: Speed (in m/s) = frequency (in Hz) x wavelength (in m) v = fλ

Wave Interactions – How Waves Behave Reflection – the bouncing back of ray of light, sound, or heat when the ray hits a surface that it does not go through. Echoes are reflections

Refraction – the bending of a wave as the wave passes Refraction – the bending of a wave as the wave passes between two substances in which the speed of the wave differs. The speed of light travels through air at 300 million m/s. The speed of light travels through water at @ 227 million m/s. The speed of light travels through glass at @ 197 million m/s.

Diffraction – a change in the direction of a wave when the wave Diffraction – a change in the direction of a wave when the wave finds an obstacle or an edge, such as an opening. Refraction occurs when waves change direction as they change speed; diffraction occurs when waves bend around an object.

Occasionally two or more waves overlap and combine to form a new wave Occasionally two or more waves overlap and combine to form a new wave. This process is called interference. In constructive interference the crests of two or more transverse waves arrive at the same place at the same time and overlap. In destructive interference, the waves subtract from each other as they overlap.

Standing Wave – a special type of wave pattern that forms when waves equal in wavelength and amplitude, but traveling in opposite directions, continuously interfere with each other. The waves create a pattern of crests and troughs that do not seem to be moving. The places where the two waves always cancel are called nodes and the wave vibrates between the nodes. https://www.youtube.com/watch?v=3BN5-JSsu_4

http://youtu.be/JppViHtLNlc

Resonance – a phenomenon that occurs when two objects Resonance – a phenomenon that occurs when two objects naturally vibrate at the same frequency; the sound produced by one object causes the other object to vibrate. https://www.youtube.com/watch?v=17tqXgvCN0E https://www.brightstorm.com/science/physics/oscillatory-motion/resonance/ https://www.youtube.com/watch?v=j-zczJXSxnw