"How Sound Spreads" Sound PPT Courseware

"How Sound Spreads" Sound PPT Courseware

Review the past and learn the new

The sound is produced due to the object ( )

All objects that are making sounds are in ( ), and such objects are called ( )

We can hear the trumpet sound because ( ) sounds at ( ); when singing, the singer’s vocal cords are at ( ); the leaves rustle when the wind blows, and the leaves are at ( ); when the drum is beaten, the drum head is at ( ) ).

Question: How does sound reach our ears?

think about it

Where does the car drive from point A to point B?

When the train goes from point A to point B, where does it run?

When a plane flies from point A to point B, where does it fly?

When the sound reaches your ears, where does it float?

Questions to be explored in this lesson

Does the propagation of sound require material? Can sound travel in a vacuum?

Does sound travel at the same speed in different materials?

What happens when sound encounters obstacles during propagation?

How does sound travel?

The vibration of an object produces sound, and when the object vibrates, it also vibrates the air around it. The vibration of the air causes our eardrums to vibrate, so that we hear the sound.

Small experiment: everyone does it

Making a native phone: Read text P34 and make a native phone for each group

Materials: two paper cups, a thin thread, needle, matchstick, tape Try your native phone: When one student speaks into the cup, can the other student hear it? Does it matter if the wire is pulled straight or not? How should your hand hold the paper cup to hear it best?

How did the sound in this experiment spread to the other party's ears? What does it mean?

Conclusion 2: Solids can transmit sound

For example, if you lie down on the rails, you can hear the sound of train wheels hitting the rails in the distance. You can hear the sounds of distant animals by lying on the ground (textbook picture P33). Many animals sleep with their ears close to the ground in order to detect the sounds of animals moving in the distance.

Both solids and gases can transmit sound

How to verify your conjecture?

group discussion. Think about examples from your life that can provide you with inferences

Example: Each group recommends a student to explain your group’s point of view

Conclusion 3: Liquids can transmit sound

Fishermen don't like people talking loudly on the shore, because the fish in the water will be scared away by the sound of talking on the shore.

When we swim, if we put our heads under the water, we can hear voices on the water and use electronic generators (sonars) to detect and fish.

What information did you get from the table above?

Sound generally travels at different speeds in different media.

The speed of sound is also related to temperature.

The speed of sound in air (15 degrees Celsius) is 340 meters per second.

Sound travels fastest in solids, followed by liquids, and slowest in gases.

The answer to the previous question:

1) Experience it: a solid table spreads sound faster than air

2) It can be heard three times at the other end of the steel pipe. The first time was from solid steel pipes, the second time was from liquid water, and the third time was from gas air.

Information Express

When sound encounters obstacles during propagation, it will be reflected back. This phenomenon is called echo.

Conditions for hearing echo: The echo reaches the human ear more than 0.1 second later than the original sound, and the human ear can hear the echo.

If the difference between the echo and the original sound is less than 0.1 seconds, the echo will be mixed with the original sound, making the original sound stronger.

Do you have an answer to the question you just asked?

During thunderstorms, we always see flashes of lightning, but hear rumbling thunder. Do you know why?

(The sound of thunder is reflected many times between the clouds and mountains and reaches human ears, so thunder is heard many times.)

Why is talking in an empty room so much louder than talking in the wild?

(In an empty room, the time difference between the echo and the original sound reaching the human ear is less than 0.1 second. The human ear cannot hear the echo. The echo strengthens the original sound, making it sound much louder than speaking in the wild.)

Application of echo

Directionally emit sound waves in the water, and use the received echoes to determine the depth of the seabed, the distance to icebergs, and discover sunken ships, schools of fish, and enemy submarines, etc.

Do the math: If it is known that the speed of sound waves propagating in seawater is 1450 meters/second, and when a survey ship on the sea surface sends a sound wave to the seafloor and receives an echo 0.8 seconds later, what is the depth of the seafloor?

Problem thinking

Why are snow days so quiet?

This is mainly because snow can absorb sound. Snow is very soft and there are many gaps in it, and sound is absorbed into these gaps.

It's not just snow that absorbs sound. Soft, inelastic materials and carpets, sofas and curtains can also absorb sound.

Sound reflection and absorption

The propagation of sound is the same as the propagation of light. Reflection and absorption will occur when encountering obstacles.

The surface of hard and smooth objects has obvious reflection effect on sound and produces echo.

Soft, rough, and porous surfaces can absorb sound and make it smaller.

Review and summary

Propagation of sound:

1. Solids, liquids, and gases can all transmit sound. Sound cannot travel through a vacuum.

2. Speed ​​of sound: At normal temperature, it is the fastest in solids and the slowest in gases.

Sound reflection and absorption:

1. Application of reflection: enhancing original sound, ranging

2. Application of absorption: sound reduction and sound insulation.

Class summary

Sound can only propagate in air, water, rope and other substances, but not in a vacuum.

Sound takes time to travel, and the speed of sound varies in different materials.

Sound will be reflected when it encounters an object during propagation; sound will be absorbed by the material during propagation.

Expand and extend

Homework: Understand what interesting phenomena in life are related to the propagation of sound, and I will share them with you in the next class.

Preliminary homework: Read pages P37-39 of the textbook, try to make a water cup piano, and try to play a simple children's song, and bring it to the next class for everyone to perform.

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