Z's 7th Grade Physics of Waves

Longitudinal Waves

A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction that the wave moves. It has compression and rarefaction Waves in which the medium moves back and forth in the same direction as the wave. Parts of compressional waves:

Types of Waves

Transverse Waves Longitudinal Waves

Characteristic of Transverse Waves

Transverse waves are always characterized by particle motion being perpendicular to wave motion.

Waves

Traveling disturbances that transmit energy from place to place.

If a wave can travel without a medium, (for example, through space),

we call it an electromagnetic wave.

Example of Longitudinal Waves

A sound wave traveling through air is a classic example of a longitudinal wave. As a sound wave moves from the lips of a speaker to the ear of a listener, particles of air vibrate back and forth in the same direction and the opposite direction of energy transport. Each individual particle pushes on its neighboring particle so as to push it forward. The collision of particle #1 with its neighbor serves to restore particle #1 to its original position and displace particle #2 in a forward direction. This back and forth motion of particles in the direction of energy transport creates regions within the medium where the particles are pressed together and other regions where the particles are spread apart. Longitudinal waves can always be quickly identified by the presence of such regions. This process continues along the chain of particles until the sound wave reaches the ear of the listener.

Transverse Waves

A transverse wave is a wave in which particles of the medium move in a direction perpendicular to the direction that the wave moves. Waves in which the medium moves at right angles to the direction of the wave.

Medium

A wave can move through matter Matter is NOT carried with the wave! Some waves do not need a medium to be able to move.

Another name of Longitudinal Waves

Compression Waves

Parts of a Longitudinal Waves

Compression: where the particles are close together Rarefaction: where the particles are spread apart

Parts of a Transverse wave

Crest: the highest point of the wave Trough: the lowest point of the wave

Wave Speed

Depends on the medium in which the wave is traveling. It varies in solids, liquids and gases.

Amplitude

How far the medium (crests and troughs, or compressions and rarefactions) moves from rest position (the place the medium is when not moving). The more energy a wave carries, the larger its amplitude.

Frequency

How many waves go past a point in one second. The unit of measurement is hertz (Hz). The higher the frequency, the more energy in the wave.

Frequency measurement examples:

If 10 waves go past in 1 second, it is 10 Hz If 1,000 waves go past in 1 second, it is 1,000Hz If 1,000,000 waves go past, it is 1,000,000 Hz

Characteristic of Longitudinal Waves

Longitudinal waves are always characterized by particle motion being parallel to wave motion.

If a wave needs a medium, we call it

Mechanical Wave

Example of Transverse Waves

Suppose that a slinky is stretched out in a horizontal direction across the classroom and that a pulse is introduced into the slinky on the left end by vibrating the first coil up and down. Energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced upwards and downwards. In this case, the particles of the medium move perpendicular to the direction that the pulse moves.

Wavelength

The distance between one point on a wave and the exact same place on the next wave.

Equation that expresses the energy of a wave

The energy of a wave can be expressed by the equation E = CA2, where E is energy, C is a constant dependent upon the medium, and A is the amplitude.

Wave Properties depend on....

Wave properties depend on what (type of energy) makes the wave. For example, you splashing in the ocean or an earthquakes creating a tsunami.

Properties of Waves

Wavelength Amplitude Frequency

Examples of waves in everyday life....

microwave ovens, medical and dental x-ray machines, eyeglasses and speakers? These are common examples in which engineers apply their knowledge of waves to design all types of useful products and tools that are evident in our everyday lives.

A mathematical way to calculate wave speed is:

wave speed = wavelength (in m) x frequency (in Hz). Or, v = f x λ. So, if a wave has a wavelength of 2 m and a frequency of 500 Hz, what is its speed? (Answer: wave speed = 2 m x 500Hz = 1000 m/s)