Characteristics of Mechanical Waves

TOP FLAP: Characteristics of a Mechanical Wave

Speed of Sound in Different Media:

Draw the spacing of particles for each type of matter (gas, solid, and liquid), note that there is an inverse relationship between the speed of sound through each type of matter and the speed of the particles.

Check your diagrams by clicking the arrow

Why does sound travel at different speeds in different materials?

Read the following passage to answer the question in your own words.

Sound waves are mechanical waves that require a medium through which to travel. The characteristics of the medium have an effect on the speed of the sound waves traveling through them. The main factors that affect the speed of sound are compressibility, stiffness, density, and temperature.

Medium: Type of matter the wave is transferring energy through, (e.g. air, water, spring)

Stiffness : In general, sound waves travel faster in materials that are stiffer, meaning harder to compress. This is because of how efficiently the movement of one particle will move another. Think of the coins, water, and air in the diagram to the right. Solids are less compressible than liquids, which are less compressible than gases. Therefore, sound waves travel fastest in solids and slowest in gases.

Density : The density of the medium also affects the speed of sound waves. Density refers to how much matter or mass there is in a given amount of space. The denser the material, the more mass it has in a given volume, so the greater its inertia. Objects with greater inertia accelerate less from an energy disturbance than objects with less inertia, or less massive objects. Therefore, in materials of the same stiffness, sound travels more slowly in the denser material.

Temperature: The temperature of a medium also affects the speed at which sound waves travel through it, though in more complicated ways. For solids, an increase in temperature reduces the stiffness, so the sound speed decreases. For fluids, such as air, the increase in temperature reduces the density, so the sound speed generally increases.

Pulse Rate

What is the relationship between your pulse rate, frequency, and wave energy?

Answer the question in your own words.

The relationship between pulse rate, frequency, and wave energy is all about how often waves happen and how much energy they carry.

First, let’s talk about pulse rate and frequency. Pulse rate is how often a wave pulse happens in a certain amount of time. If you think about waves in water, it’s like counting how many ripples reach the shore every second. This is also called frequency, and we measure it in something called hertz (Hz). So, if more pulses happen in less time, the frequency is higher. They’re directly connected: higher pulse rate means higher frequency.

Now, let’s connect frequency to wave energy. Waves with a higher frequency (meaning more pulses per second) usually carry more energy. For example, think about how sunlight feels warmer at noon when the rays (high-frequency light waves) are more direct compared to early morning or evening. In science, energy is linked to frequency, especially for things like light and sound waves. The higher the frequency, the more energy the wave has.

Finally, since pulse rate and frequency are tied together, an increase in pulse rate also increases the wave energy, as long as the wave size (called amplitude) stays the same. Imagine shaking a rope back and forth faster—you’re putting more energy into it, so the waves become stronger.

In short, when you increase the pulse rate, you increase the frequency, and higher frequency means more wave energy!

BOTTOM FLAP: Characteristics of a Mechanical Wave

Fill out the missing words and draw the diagrams as described in the directions.

You can use the PBS Wave Interactive to help you create your diagrams.

Amplitude

The maximum height of the peaks above the resting line in a wave "Rest to crest".

⬆Amplitude = ⬆Energy.

In the space below, draw 2 transverse waves with differing amplitude. Be sure to label which amplitude is greater.

Amplitude Example Diagram

Frequency

The number of wave cycles that pass by a fixed point in 1 second.
Measure in Hertz (Hz), 1 Hertz = 1 wave cycle / 1 second

⬆Frequency = ⬆Hertz = ⬆Energy.

In the space below, draw 2 transverse wave sequences with differing frequency. Be sure to label which frequency is greater.

Frequency Example Diagram

Wavelength (λ)

The length of 1 wave, can be measured as the distance from crest to crest.
Shown with the λ (lambda) symbol.

⬇Wavelength = ⬆Energy.

In the space below, draw 2 transverse waves with differing wavelength. Be sure to label which wavelength is greater. If you have room, add the wavelength of a longitudinal wave.

Wavelength Example Diagram

You can use any two repeating points for wavelength, crest-crest, trough-trough, or any point, as long as it contains a full wave pattern, so a whole crest and trough.

Wave Speed

The distance a wave travels in a certain amount of time.

Measured as a rate (m/s).

Speed is dependent on the medium.

⬆Wave Speed = ⬆Energy.

To calculate a wave’s speed, divide the distance it travels by the time it takes to travel that distance. You can also find a wave’s speed if you know its wavelength and frequency—just multiply wavelength times frequency.

Wave speed=Wavelength×Frequency

In the space below, recreate the diagram and calculate the wave speed in m/s.

Wave Speed Answer Key

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