Vibration of sound
Sound can be heard when air or the like transmits vibrations. Here, we will conduct an experiment to visually capture the state of the vibration and consider it in a little more detail.
Experiment 1: Let's see the vibration caused by sound
An object is called a natural frequency and resonates at a specific frequency. Put vinyl on the basin and sprinkle with table salt to make a loud voice. A pattern can be created at a certain voice pitch (frequency).
Cut the black plastic bag and stick it to the basin. Make a small hole in the corner to eliminate the pressure difference from the outside. After that, cover your mouth with a paper cup so that you do not breathe directly, and vibrate loudly while changing the pitch of your voice. You can make a pattern with a voice of a certain height. It's a little difficult.
A pattern is formed when a constant vibration is transmitted to the vinyl film. Such constant vibration is called a standing wave. This standing wave is divided into a part that vibrates violently and a part that does not vibrate very much. Table salt gathers in the non-vibrating part and draws a pattern. It's okay to make the tea muddy with this, but I'll make it a little more serious. It is called a Chladni figure.
Experiment 2: Let's see the vibration caused by sound ② (Let's see the Chladni figure)
you need : Square aluminum plate, speaker, black magic, table salt, sound source software that can output a specific frequency
Connect the sound source to the speaker. If possible, insert an amplifier to make the sound louder. Paint a square aluminum plate black and place it on the speaker. It is better to fix it with bolts, but I just put it because it can not be used for other experiments. Sprinkle table salt (which does not harden more than salt) and make a sound to create a pattern. This is called a Chladni figure.
Experiment 3: Let's see the vibration caused by sound ③ (Let's see the vibration caused by the Kunt tube)
you need : transparent cylinder, table salt, sound source software that can output specific frequencies, speakers
This is a high school experiment. Connect a clear plastic tube to the speaker. Put fine styrofoam grains (in the pillow) and cover. As shown in the photo on the left, the grains vibrate cleanly at a certain frequency according to the length of the tube.
When becomes standing wave (most firmly resonance) as shown in the left in the tube, 2 times the wavelength of the sound in the case of upper tube: (f = 2L L is the length of the tube) following acoustic velocity 340m / s Substitute in the formula of. V = f × λ Frequency λ can be calculated.
In the case of the figure below, the length of the tube is the wavelength f.
Experiment 4: Let's see the vibration caused by sound ④ (Let's make a dancing snake)
you need : Paper cup, color drawing paper, molding 4 cm, cutter
Make a hole about 2 cm in diameter in the paper cup. Make a snake with a tongue in the mall. Pay attention to the balance. Place the snake on the cup and use a megaphone made of drawing paper to speak into the hole. A snake spins around with a sound of a certain height.
Experiment 5: Let's see the frequency visually (let's make a buzzing balloon)
you need : 3 balloons, 3 nuts of different sizes
Insert hexagon nuts of different sizes and inflate the balloon to the same size. You can make a sound by turning it around. Have students calculate the frequency.
A balloon with a diameter of 15 cm was put in a nut with a side of 0.3 cm and rotated. (1) What is the circumference of the balloon (15 x 3.14 = 47.1 cm)? (2) How many times does the corner hit the balloon assuming that the hexagonal nut hits the balloon properly? (47.1 ÷ 0.3 = 157 times) ③ Listen and compare the sound of 157Hz and the sound of balloons. The pitch is quite close.