In this article, we’ll look at the factors that affect the speed of sound and how to measure it. Sound travels through air at a speed of about 340m/s at sea level at 20°C. What does this tell us? Air temperature and pressure affect how fast sound can travel through the air. And this speed varies again for different media. How can it be related to particles?
Thus, sound travels through air at a speed of about 340 meters per second. In water, it moves at a speed of 1500 meters per second. Although sound can travel up to 5000 meters per second in some solids which is extremely fast compared to air. These differences are due to the way particles are arranged in solids, liquids, and gases.
In solids, particles are fixed in rows touching each other. in liquids, particles remain touching each other but some gaps are present and in gases, particles are far apart occasionally colliding with each other.
So what’s the relationship between the distance between the particles and the speed at which sound travels? pause the article and have a think
The closer the particles lie the faster sound is able to travel. sound waves travel faster through solids and liquids because their particles are closer together so it’s easier for the vibration to hit the next particle. another way of saying this is the more densely the particles are arranged the faster sound travels.
So now we can link this idea to how temperature affects the speed of sound in air. when temperature increases the kinetic energy of particles also increases in a gas, the particles collide more often at higher temperatures passing on the vibrations. so the sound will travel faster as the temperature of the gas increases.
What about air pressure?
At sea level, the air particles are more densely packed than at altitude. this means at sea level the vibrations of sound pass more quickly between particles and sound travels faster.
How does changing the speed of the wave affect the frequency and wavelength of a wave?
You should already know how to use the wave equation. when the speed of sound changes as it enters a different medium the frequency remains the same but the wavelength changes the frequency cannot change as it is set by the source of the sound.
So as speed increases wavelength increases as speed decreases wavelength also decreases. for example as sound moves from air to water it speeds up because the particles are closer together in the water than in the air. as the speed of the sound wave increases so does the wavelength.
Can you think of an easy experiment you could do to measure the speed of sound?
One option is to get someone to stand exactly 400 meters away with a stopwatch. make sure you can clearly see each other. when you are both ready loudly bang the drum with your drumstick your partner starts the clock when they see you hitting the drum and stops it when they hear the sound. repeat this experiment a number of times then take the average of all the readings. we can now work out the speed using the equation speed equals distance over time. so speed equals 400 meters divided by 1.2 giving a speed of 333 meters per second. pretty close to 340 meters per second but not exactly the same.
Think of reasons why the speed isn’t 340m/s.
Maybe it’s colder than 20 degrees celsius or maybe we’re at a higher altitude than sea level or maybe it’s a human error that the stopwatch timer had slightly delayed reactions.
So we’ve seen that the speed of sound waves varies between solids liquids and gases because of how closely or far apart molecules are for the vibrations to pass between atmospheric pressure and temperature also affect the speed.