Waves

The Nature of Waves

What is in a wave? A wave is a repeating disturbance or movement that transfers energy through matter or space. A wave is a repeating disturbance or movement that transfers energy through matter or space. For example, during earthquakes, energy is transferred in powerful waves that travel through Earth. For example, during earthquakes, energy is transferred in powerful waves that travel through Earth.

Wave and Energy A pebble falls into a pool of water and ripples form.A pebble falls into a pool of water and ripples form. Because it is moving, the falling pebble has energy.Because it is moving, the falling pebble has energy.

As it splashes into the pool, the pebble transfers some of its energy to nearby water molecules, causing them to move.As it splashes into the pool, the pebble transfers some of its energy to nearby water molecules, causing them to move. What you see is energy traveling in the form of a wave on the surface of the water.What you see is energy traveling in the form of a wave on the surface of the water. RaftRaft

The waves don’t even carry the water along with them. The waves don’t even carry the water along with them. Only the energy carried by the waves moves forward. Only the energy carried by the waves moves forward. All waves have this property All waves have this property They carry energy without transporting matter from place to place. They carry energy without transporting matter from place to place.

Making Waves A wave will travel only as long as it has energy to carry.A wave will travel only as long as it has energy to carry. Anything moving up and down or back and forth in rhythm is vibrating.Anything moving up and down or back and forth in rhythm is vibrating. All waves are produced by vibrating matterAll waves are produced by vibrating matter

Mechanical Waves Some wave require matter to transfer the energy.Some wave require matter to transfer the energy. The matter the waves travel through is called a medium.The matter the waves travel through is called a medium. The medium can be a solid, a liquid, a gas, or a combination of these.The medium can be a solid, a liquid, a gas, or a combination of these.

The two types of mechanical waves are transverse waves and compressional waves.The two types of mechanical waves are transverse waves and compressional waves.

Transverse Wave In a transverse wave, matter in the medium moves back and forth at right angles to the direction that the wave travels.In a transverse wave, matter in the medium moves back and forth at right angles to the direction that the wave travels. For example, a water wave travels horizontally as the water moves vertically up and down.For example, a water wave travels horizontally as the water moves vertically up and down.

Compressional Waves In a compressional wave, matter in the medium moves back and forth along the same direction that the wave travels.In a compressional wave, matter in the medium moves back and forth along the same direction that the wave travels. The wave carries energy, but not matter, forward along the spring.The wave carries energy, but not matter, forward along the spring.

Compressional waves also are called longitudinal wavesCompressional waves also are called longitudinal waves Sound creates compressional waves.Sound creates compressional waves.

Deep Water Waves A water wave causes water to move back and forth, as well as up and down.A water wave causes water to move back and forth, as well as up and down. This motion causes both transverse and compressional wavesThis motion causes both transverse and compressional waves

Seismic Waves Forces in Earth’s crust can cause regions of the crust to shift, bend, or even break.Forces in Earth’s crust can cause regions of the crust to shift, bend, or even break. The breaking crust vibrates, creating seismic waves that carry energy outward.The breaking crust vibrates, creating seismic waves that carry energy outward.

Seismic waves are a combination of compressional and transverse waves.Seismic waves are a combination of compressional and transverse waves. They can travel through Earth and along Earth’s surface.They can travel through Earth and along Earth’s surface.

Wave Properties

The Parts of a Wave Transverse waves and compressional waves have different characteristics: crests and trough, compressions and rarefactions.Transverse waves and compressional waves have different characteristics: crests and trough, compressions and rarefactions. They also have similar properties: wavelength, frequency, period, amplitude, and wave speed.They also have similar properties: wavelength, frequency, period, amplitude, and wave speed.

The Parts of a Transverse Wave A transverse wave has alternating high points, crests, and low points, troughs.A transverse wave has alternating high points, crests, and low points, troughs. Rest position is also called equilibrium.

Wavelength of Transverse Wave A wavelength,, is the distance between one point on a wave and the nearest point just like it.A wavelength,, is the distance between one point on a wave and the nearest point just like it. Wavelength is the distance from crest to crest or trough to trough.Wavelength is the distance from crest to crest or trough to trough.

The Parts of a Compressional Wave A compressional wave has regions where the particles are close together, compressions.A compressional wave has regions where the particles are close together, compressions. And regions where the particles are further apart, rarefactions.And regions where the particles are further apart, rarefactions.

The wavelength of a Compressional Wave A wavelength is the distance between two neighboring compressions or two neighboring rarefactions.A wavelength is the distance between two neighboring compressions or two neighboring rarefactions.

Amplitude Amplitude is related to the energy carried by a wave.Amplitude is related to the energy carried by a wave. The greater the wave’s amplitude is, the more energy the wave carries.The greater the wave’s amplitude is, the more energy the wave carries.

Amplitude of a Transverse Wave The amplitude is the distance from the crest or trough of the wave to the rest position of the medium.The amplitude is the distance from the crest or trough of the wave to the rest position of the medium.

The Amplitude of a Compressional Wave The amplitude of a compressional wave is related to how tightly the medium is pushed together at the compressions.The amplitude of a compressional wave is related to how tightly the medium is pushed together at the compressions. The denser the medium is at the compressions, the larger its amplitude is and the more energy the wave carries.The denser the medium is at the compressions, the larger its amplitude is and the more energy the wave carries.

Frequency, f The number of wavelengths that pass a fixed point each second.The number of wavelengths that pass a fixed point each second. The rate of vibrationThe rate of vibration Find the frequency of a transverse wave by counting the number of crests or troughs that pass by a point each second.Find the frequency of a transverse wave by counting the number of crests or troughs that pass by a point each second. Expressed in Hertz (Hz).Expressed in Hertz (Hz).

Period, T The amount of time it takes one wavelength to pass a point.The amount of time it takes one wavelength to pass a point. As the frequency of a wave increases, the period decreases.As the frequency of a wave increases, the period decreases. Units of seconds, s.Units of seconds, s.

Frequency & Period The frequency, f, and period, T, are reciprocals of each other. The frequency, f, and period, T, are reciprocals of each other.

Speed of a Wave The speed of a wave depends on the medium it is traveling through.The speed of a wave depends on the medium it is traveling through. Sound travels faster in solids than gases.Sound travels faster in solids than gases. Light travels faster in air than water.Light travels faster in air than water.

Calculating the Speed of a Wave v=f v=f Where: Where: v is speed in m/s v is speed in m/s f is frequency in Hz f is frequency in Hz  is wavelength in m  is wavelength in m