Mechanical Waves

What are waves? Wave – a disturbance that transfers energy from place to place. Medium – the material thru which a wave passes Waves travel trough the medium without actually moving the medium with it.

Two Categories of Waves Mechanical These are waves that transfer energy through matter They require a medium (Solid, liquid, or gas) Examples of Mechanical Waves: Transverse and Longitudinal waves Electromagnetic These are waves that transfer energy through a field They do NOT require a substance to travel through Examples of Electromagnetic Waves: Microwaves and Cellular Phones

Types of Mechanical Waves: • Transverse Waves: waves that move the medium at right angles to the direction in which the waves are traveling. • Longitudinal Waves: move particles parallel to the direction the wave is moving, “push-pull” waves.

Wave Particle Movement Waves travel trough the medium without actually moving the medium with it. Basically the medium stays put while the wave moves some distance.

How do we know waves carry energy and not matter? Think about an earthquake. When seismic waves travel through an area, the ground shakes from side to side and up and down, but the ground itself does not travel over a distance. Only the ENERGY moves!

Properties of Waves • Amplitude – in a transverse wave – the height away from the “rest” position. The amplitude in a longitudinal wave is the measure of how compressed or rarefied the medium becomes. • Wavelength – the distance between two corresponding parts of a wave. • Frequency – the number of complete waves that pass a given point in a certain period of time. Frequency is measured in HERTZ, one Hz is a wave that occurs once every second.

So what makes a wave?

Longitudinal waves create points called compressions and rarefactions. Compressions: parts where the coils are close together Rarefactions: parts where the coils are spread out

What causes waves? You MUST have energy. Mechanical waves are produced when a source of energy causes a medium to vibrate. A vibration is a repeated back-and-forth or up-and- down motion. When a vibration moves through a medium, a wave results.

Examples

How do we calculate WAVE SPEED?

Waves can also be reflective and refractive Waves can bounce off of something after striking it. That is a reflection. Sound and light waves can equally be reflective in nature and bounce energy wave back with equal force. Example) screaming in a canyon There are also times waves can not bounce back. Waves can bend at a different angle and refract. This occurs when wave energy is travel at a different speed than the medium.

Interactions of Waves • Diffraction – Wave passing a barrier or going through a hole in a barrier bends and causes the wave to wrap around the barrier.

Vocabulary Medium Wave Reflection Refraction Amplitude Compression Crest Longitudinal Rarefaction Transverse Trough Wavelength Frequency Mechanical