- Sound questions
- Sound is a longitudinal wave
- Production of sound
- Sound Properties: Amplitude, period, frequency, wavelength
- Speed of Sound
- Relative speed of sound in solids, liquids, and gases
- Decibel Scale
- Why do sounds get softer?
- Ultrasound medical imaging
- Standing waves in open tubes
- Standing waves in closed tubes
- Doppler effect introduction
- Doppler effect formula for observed frequency
- Doppler effect formula when source is moving away
- When the source and the wave move at the same velocity
- Doppler effect for a moving observer
- Doppler effect: reflection off a moving object
Sounds travels at different speeds in different media. Created by David SantoPietro.
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- What exactly is the Bulk's modulus? I understand that it is a measure of rigidity, but how do we define rigidity? Is there a formula? What's the difference between rigidity and pressure if both of them are measured in Pascals?(33 votes)
- Please explain how echoes are formed - and how the angle of incidence is equal to the angle of reflection and why only sometimes you can hear echoes and sometimes you can't. Then also the calculations to figure out how far you are from a sound reflective surface (e.g. how steep a cliff is)(8 votes)
- When a sound wave meets a change in medium, it splits. Some of it goes through, some is reflected back. Your brain is weird sometimes. If you hear 2 similar sounds in a small interval of time, your brain will hear them as just 1 sound.
For you to notice the echo, the wall reflecting the wave back has to be far enough way so that it takes more time for the wave to go and come back, enough for your brain to listen 2 different sounds.
As for the angles, it's very hard to explain it in words. I made a program that simulates a similar behavior for light, which works in the same way sounds does in regards to reflections. Try it out: https://www.khanacademy.org/computer-programming/light-reflection-and-refraction/5872552844722176
Hope it helps :D(16 votes)
- What about hot humid air? Would the speed of sound be faster or slower than room temperature, non humid air?(7 votes)
- Why is it so that light, an electromagnetic transverse wave slows down in denser medium but sound, a mechanical transverse wave travels faster in a denser medium??(5 votes)
- They are totally different types of waves. There's no reason to expect an electromagnetic wave that requires no medium to behave the same as a mechanical wave that does require a medium.(7 votes)
- Does density matter? My textbook, College Physics - a strategic approach by Knight/Jones/Field, states, "The speed of sound doesn't depend on the pressure or the density of the gas" on page 474 in chapter 15 on Traveling Waves and Sound. Who's right - Khan or Knight?(4 votes)
- The speed depends on both pressure AND density but the effects cancel out, and for an ideal gas you cannot increase pressure without also increasing density (holding temperature constant). Air is pretty close to an ideal gas so the speed only depends on the temperature (which in turn affects pressure and density, but as stated before, they cancel out)
- We know that sound energy can travel through gases and solids. Then why does it gets reflected by walls and does not pass through it?(4 votes)
- Some of it gets reflected just like how when a water wave reaches land some of the water gets reflected back to the center of the waves. So you might be able to hear a small echo. But some passes through just like how some water in a water wave flows or splashes onto the upper surface of the land and gets absorbed and some of the land in the deeper parts of the body of water absorb the water that travels in waves. When it passes through just like how you or nature can change the speed of the water waves, the sound speeds up. However because of how some gets reflected in the solid which makes the molecules in the solid vibrate against each other more it produces heat instead of an echo. This dampens the vibrations so speed increases and amplitude decreases and then speed decreases again but the amplitude doesn't change. So you can hear what is going on next door to your house because of how the sound passes through room temperature air and then their walls and then outside temperature air and then your walls and then room temperature air again and into your ears. However because of dampening it is much quieter where you are then it is where the sound source is and not just a little bit quieter because of distance.(4 votes)
- Why exactly sounds waves are after in denser materials? I thought the more numerous of molecules per metre cubic will "help" waves propagate..(4 votes)
- This has more to do with the interaction of macroscopic mechanical properties of the material being considered. Sound waves propogate via vibration of the medium, provoking an interaction between bulk material constants such as lame's constant, elasticity modulus, poisson's ratios, and density. A quick search on dilatational wave speed will show increasing density decreases wave propagation speed.(3 votes)
- Does the formula mentioned in this video have a title?(4 votes)
- It's not Newton- Laplace equation .its only Newtons equation because Newton Laplace equation has a "gamma" in the numerator called Adiabatic elasticity n moreover the equation given in the video is applicable only at constant temperature(isothermal) and that of Newton Laplace equation is applicable at Adiabatic conditions ..(2 votes)
- Isn't it not density which makes the speed of sound faster ?(1 vote)
- It's not only density. It also can involve a metric called the bulk modulus, which is related to density, for a gas. And for a solid or liquid it also involves something called the shear modulus.(2 votes)
- Now I didn't get one thing what's the difference between rigidity and density ?(0 votes)
- an iron girder is rigid because it is difficult to bend.
rigid is opposite to flexible
gold is dense because it has a lot of mass in a small volume(4 votes)
- [Voiceover] To change the speed of sound you have to change the properties of the medium that sound wave is traveling through. There's two main factors about a medium that will determine the speed of the sound wave through that medium. One is the stiffness of the medium or how rigid it is. The stiffer the medium the faster the sound waves will travel through it. This is because in a stiff material, each molecule is more interconnected to the other molecules around it. So any disturbance gets transmitted faster down the line. The other factor that determines the speed of a sound wave is the density of the medium. The more dense the medium, the slower the sound wave will travel through it. This makes sense because if a material is more massive it has more inertia and therefore it's more sluggish to changes in movement or oscillations. These two factors are taken into account with this formula. V is the speed of sound. Capital B is called the bulk modulus of the material. The bulk modulus is the official way physicists measure how stiff a material is. The bulk modulus has units of pascals because it's measuring how much pressure is required to compress the material by a certain amount. Stiff, rigid materials like metal would have a large bulk modulus. More compressible materials like marshmallows would have a smaller bulk modulus. Row is the density of the material since density is the mass per volume, the density gives you an idea of how massive a certain portion of the material would be. For example, let's consider a metal like iron. Iron is definitely more rigid and stiff than air so it has a much larger bulk modulus than air. This would tend to make sound waves travel faster through iron than it does through air. But iron also has a much higher density than air, which would tend to make sound waves travel slower through it. So which is it? Does sound travel faster though iron or slower? Well it turns out that the higher stiffness of iron more than compensates for the increased density and the speed of sound through iron is about 14 times faster than through air. This means that if you were to place one ear on a railroad track and someone far away struck the same railroad track with a hammer, you should hear the noise 14 times faster in the ear placed on the track compared to the ear just listening through the air. In fact, the larger bulk modulus of more rigid materials usually compensates for any larger densities. Because of this fact, the speed of sound is almost always faster through solids than it is through liquids and faster through liquids than it is through gases because solids are more rigid than liquids and liquids are more rigid than gases. Density is important in some aspects too though. For instance, if you heat up the air that a sound wave is travelling through, the density of the air decreases. This explains why sound travels faster through hotter air compared to colder air. The speed of sound at 20 degrees Celsius is about 343 meters per second, but the speed of sound at zero degrees Celsius is only about 331 meters per second. Remember, the only way to change the speed of sound is to change the properties of the medium it's travelling in and the speed of sound is typically faster through solids than it is through liquids and faster through liquids than it is through gases.