When you wet your fingers and rub them along the rim of a goblet glass, what do you hear? 20

A creaking sound is heard, and the principle of this sound is from frictional vibration.

Friction vibration, also known as stick-slip motion, is a common phenomenon in engineering. These phenomena are most prevalent when the sliding speed is very low, often resulting in not only noise, but also severe wear and dimensional inaccuracy.

Causes of friction and vibration:

1. Due to the adhesion between the two friction surfaces.

2. Due to friction.

Decreases as the sliding speed increases.

3. Because the friction increases with the extension of the static contact time.

The vibrating principle of sound.

Sound is a pressure wave that causes the rhythmic vibration of the medium-air molecules when playing an instrument, striking a door, or knocking on a tabletop, causing the surrounding air to produce a dense change in the longitudinal waves.

This creates sound waves, a phenomenon that continues until the vibrations disappear.

Sound as a type of wave, frequency and amplitude.

It becomes an important property to describe the wave, the magnitude of the frequency corresponds to what we usually call the pitch, and the amplitude affects the magnitude of the sound. Sound can be broken down into sine waves of different frequencies and intensities.

of the superposition. This process of transformation (or decomposition) is called the Fourier transform.

fourier transform)。

There will be a creaking sound.

The more water you add, the lower the tone, and the less water you add, the higher the tone. When your fingers rub against the glass, the glass vibrates and sends a sound into the surrounding air. However, if water is added to the cup, the sine wave generated by the vibration of the glass and the water will collide with each other to produce standing waves, which will cause the vibration frequency to drop and the sound tone to become lower.

The number of vibrations of a vibrating object per unit of time is often represented by the symbol f, and the unit of frequency is the second of seconds, also known as hertz. The vibrational frequency indicates how fast or slow the object vibrates, and in the pathogenic effect of vibration, frequency plays an important role. Large-amplitude and low-frequency (below 20 Hz) vibrations mainly act on the vestibular organs and displace the internal organs; The small amplitude and high frequency vibration mainly affect the central nervous system and nerve endings in various tissues.

Related information

The vibration frequency f is the number of vibration cycles of an object per second, and the SI unit is hertz [Hz]. Frequency is a sign of vibration characteristics and an important basis for analyzing the causes of vibration. The vibration frequency meter is developed for measuring the working frequency of various vibrating rollers, and can also be used to measure the vibration frequency of general machinery and equipment.

The instrument is made of large-scale integrated circuits and high-sensitivity sensors, which has the characteristics of high reliability, low power consumption and strong anti-interference ability. The instrument adopts ABS handheld casing and battery power supply, and the frequency value is displayed in LED mode, which is easy and intuitive to operate. The successful development of this instrument will greatly facilitate the testing of mechanical equipment by testers on site.

Finger rubbing. The glass, the glass is shocked and begins to vibrate, and a sound is transmitted into the surrounding air. If water is added to the cup, the sine wave generated by the vibration of the glass and the water will collide with each other.

Standing waves, which cause the frequency of the vibration to drop and the tone of the sound to become lower. The more water you add, the lower the tone, and the less water you add, the higher the tone.

As shown in the figure, when you rub the mouth of the goblet with your hand dipped in water, you hear the sound of the cup, and when the amount of water injected into the cup changes, the tone in the sound characteristics changes, and when the amount of water increases, the characteristics of the sound become higher.

The pitch of the sound is called the pitch, and the frequency determines the pitch.

The faster the object vibrates, the higher the pitch of the sound.

The slower the vibration, the lower the pitch of the sound is one of the three main subjective properties of sound, namely volume (also known as loudness), tone, and timbre (also known as sound). It indicates the degree to which a person's hearing can distinguish the tone of a sound. The pitch is mainly determined by the frequency of the sound and is also related to the intensity of the sound.

For pure tones of a certain intensity, the pitch rises and falls with the rise and fall of frequency; The pitch of a certain frequency of pure tone and low frequency pure tone decreases with the increase of sound intensity, while the tone of high-frequency pure tone increases with the increase of intensity.

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Sound is a pressure wave: when a musical instrument is played, a door is slammed or a table is struck, their vibrations cause the medium-air molecules to vibrate rhythmically, causing the surrounding air to produce dense changes to form sparse longitudinal waves, which produce sound waves, and this phenomenon continues until the vibration disappears.

As a kind of wave, frequency and amplitude have become important properties to describe the wave, the magnitude of the frequency corresponds to what we usually call pitch, and the amplitude affects the magnitude of the sound. Sound can be broken down into superpositions of sine waves of different frequencies and intensities. This process of transformation (or decomposition) is called the Fourier transform.

Therefore, sound in general always contains a certain frequency range. The frequency range of sounds that can be heard by the human ear is between 20 and 20,000 hertz. Fluctuations above this range are called ultrasound, while those below this range are called infrasound.

Animals such as dogs and bats can hear sounds up to 160,000 hertz. Whales and elephants produce sounds with frequencies in the range of 15 to 35 Hz.

The propagation of sound is explained by quantum mechanics as the movement of atoms, which forms sound waves. But this is not related to nouns such as wave particles.

Answer: Pitch, high.

When we rub the mouth of the cup with our fingers dipped in water, the cup will make a sound due to vibration, if we only change the amount of water injected into the cup, the frequency of the cup vibration will change, and the tone will also change, that is, under the action of the same force, the frequency of the cup vibration will become faster, and the tone will become higher.

When rubbing the mouth of the cup with a finger dipped in water, the cup only changes the amount of water injected into the cup due to the sound of vibration, the frequency of the cup vibration changes, and the tone changes, that is, under the action of the same force, the more water, the less likely it is to vibrate, and the slower the cup vibrates, so the frequency of its vibration slows down and the tone becomes lower

So the answer is: tone; Low

Why does a goblet sing?

Because when we rub the rim of the cup with our hands dipped in water, the cup will make a sound as soon as it is vibrate. So the goblet will sing.

In the experiment as shown in the figure, when the fingers are moistened and rubbed along the edge of the cup, it is the cup and the water that vibrate, and when the amount of water is larger, the more difficult it is for the cup and water to vibrate, so it can be concluded that the larger the amount of water in the cup, the lower the tone, and the smaller the amount of water, the higher the pitch Therefore, only option d is in line with the topic

Therefore, choose D