Question 1

What is the difference between frequency and pitch?

Accepted Answer

Frequency is an objective, measurable physical property of a wave, defined as the number of cycles per second (Hertz). Pitch is a subjective, psychological perception created by the human brain. While pitch is primarily determined by frequency (higher frequency results in higher perceived pitch), pitch can also be slightly influenced by the sound's volume and the physical structure of the listener's ear. A wave calculator only deals with frequency.

Question 2

Can sound travel in a vacuum or in space?

Accepted Answer

No. Sound is a mechanical wave, meaning it requires a physical medium—atoms or molecules—to bump into one another to transfer energy. In the vacuum of space, there is no air, gas, or liquid to compress and expand. Therefore, sound cannot propagate at all. Electromagnetic waves, however, like light and radio, are self-propagating fields and travel perfectly well through the vacuum of space.

Question 3

Why does sound travel faster in water than in air?

Accepted Answer

The speed of a mechanical wave is determined by the density and the elastic modulus (stiffness) of the medium. While water is much denser than air (which would normally slow a wave down), it is exponentially more rigid and incompressible than air. The stiffness factor vastly outweighs the density factor. Because the water molecules are packed tightly together and strongly resist compression, they transfer acoustic kinetic energy to their neighboring molecules much faster than the widely spaced molecules in a gas.

Question 4

What happens to a wave's properties when it moves from air into water?

Accepted Answer

When any wave transitions from one medium to another, its velocity changes because the new medium has different physical properties. Because the velocity changes, the wavelength must also change proportionally. However, the frequency of the wave remains absolutely identical. The frequency is permanently locked in by whatever source originally created the wave. If a $400$ Hz sound wave enters the water, it speeds up, its physical wavelength stretches out to become longer, but it remains exactly $400$ Hz.

Question 5

How do you calculate the frequency of a wave if you only know the period?

Accepted Answer

You do not need to know the velocity or wavelength to find frequency if you have the period. Frequency and period are inversely related. The formula is simply $f = 1 / T$. If a pendulum takes exactly $2$ seconds to complete one full swing back and forth, its period ($T$) is $2$. Its frequency is $1 / 2$, which equals $0.5$ Hz. This means it completes half a cycle per second.

Question 6

What does it mean when two waves are "out of phase"?

Accepted Answer

Phase refers to the horizontal alignment of two waves. If two sound waves of the exact same frequency have their peaks and troughs perfectly aligned at the same time, they are "in phase" and will constructively interfere, making the sound louder. If one wave is shifted horizontally so that its peak aligns exactly with the trough of the other wave, they are 180 degrees "out of phase." In this scenario, the high pressure of one wave is perfectly canceled by the low pressure of the other, resulting in complete silence. This is exactly how active noise-canceling headphones calculate and destroy background noise.

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