I know a car sounds different approaching vs leaving but what is happening re sound waves and is there a similar effect with light waves?
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You’re literally running into/away from sound waves, causing you to receive more or less waves so they sound differently.
The same phenomenon is also present on lights but for very different reasons. Everyone approaches light at the same speeds, but the definition of space and time changes, making the light to appear to change in frequency.
It helps to think of the wave as a series of baseballs being flung at you. Each peak being a ball. And these balls are magic balls that always travel at the same speed, regardless of the velocity of thing throwing them.
Now say you mounted a gun that shot these baseballs at a set interval on top of a car.
Let’s say it fires balls one per second, no matter the speed of the car. These balls travel at 100 meters per second, no matter what the speed of the car.
But the car is also traveling towards you at 10m/s. So each subsequent ball, while traveling the exact same speed, has to cover a shorter distance to reach you. If the first ball is fired at 1000 meters, it takes ten seconds to reach you. The next takes 9.9, the next 9.8….
So the frequency of balls hitting you increases, even though they are leaving the source at a constant interval.
Driving away, it’s the opposite. The balls have to cover increasing distances every time, so they hit you les and less frequently.
And yes, this applies to light. You may have heard the terms “red shift” and “blue shift” which correspond to the lowering and raising of electromagnetic wave frequency as objects move away or towards the observer. Red light is the lower frequency end of the visible light spectrum, and blue the higher. The terms can apply to frequencies outside the visible spectrum as well though.
You’re literally running into/away from sound waves, causing you to receive more or less waves so they sound differently.
The same phenomenon is also present on lights but for very different reasons. Everyone approaches light at the same speeds, but the definition of space and time changes, making the light to appear to change in frequency.
You’re literally running into/away from sound waves, causing you to receive more or less waves so they sound differently.
The same phenomenon is also present on lights but for very different reasons. Everyone approaches light at the same speeds, but the definition of space and time changes, making the light to appear to change in frequency.
Say you’re standing on the ocean shore and the waves are splashing on your feet at a steady interval. If you run out into the ocean you will get hit with more waves than standing still over the same amount of time. Now run back out of the water. You probably aren’t fast enough to outrun all the waves but you’ll be hit by fewer than when standing still.
When it comes to sound the energy in the noise is constant, like a 3ft string will always be 3ft long but you can make a wave that is 3″ long but the top and bottom would have to be pretty high compared to the string laid flat or with a slight wave.
So the ambulance moving closer while using the siren means that more waves hit you faster, the waves have to change shape and get taller to keep the same energy. Taller waves sound higher. Then the reverse happens when it’s moving away. The energy always stays the same it just changes shape to fit in the space available
Say you’re standing on the ocean shore and the waves are splashing on your feet at a steady interval. If you run out into the ocean you will get hit with more waves than standing still over the same amount of time. Now run back out of the water. You probably aren’t fast enough to outrun all the waves but you’ll be hit by fewer than when standing still.
When it comes to sound the energy in the noise is constant, like a 3ft string will always be 3ft long but you can make a wave that is 3″ long but the top and bottom would have to be pretty high compared to the string laid flat or with a slight wave.
So the ambulance moving closer while using the siren means that more waves hit you faster, the waves have to change shape and get taller to keep the same energy. Taller waves sound higher. Then the reverse happens when it’s moving away. The energy always stays the same it just changes shape to fit in the space available
It helps to think of the wave as a series of baseballs being flung at you. Each peak being a ball. And these balls are magic balls that always travel at the same speed, regardless of the velocity of thing throwing them.
Now say you mounted a gun that shot these baseballs at a set interval on top of a car.
Let’s say it fires balls one per second, no matter the speed of the car. These balls travel at 100 meters per second, no matter what the speed of the car.
But the car is also traveling towards you at 10m/s. So each subsequent ball, while traveling the exact same speed, has to cover a shorter distance to reach you. If the first ball is fired at 1000 meters, it takes ten seconds to reach you. The next takes 9.9, the next 9.8….
So the frequency of balls hitting you increases, even though they are leaving the source at a constant interval.
Driving away, it’s the opposite. The balls have to cover increasing distances every time, so they hit you les and less frequently.
And yes, this applies to light. You may have heard the terms “red shift” and “blue shift” which correspond to the lowering and raising of electromagnetic wave frequency as objects move away or towards the observer. Red light is the lower frequency end of the visible light spectrum, and blue the higher. The terms can apply to frequencies outside the visible spectrum as well though.
It helps to think of the wave as a series of baseballs being flung at you. Each peak being a ball. And these balls are magic balls that always travel at the same speed, regardless of the velocity of thing throwing them.
Now say you mounted a gun that shot these baseballs at a set interval on top of a car.
Let’s say it fires balls one per second, no matter the speed of the car. These balls travel at 100 meters per second, no matter what the speed of the car.
But the car is also traveling towards you at 10m/s. So each subsequent ball, while traveling the exact same speed, has to cover a shorter distance to reach you. If the first ball is fired at 1000 meters, it takes ten seconds to reach you. The next takes 9.9, the next 9.8….
So the frequency of balls hitting you increases, even though they are leaving the source at a constant interval.
Driving away, it’s the opposite. The balls have to cover increasing distances every time, so they hit you les and less frequently.
And yes, this applies to light. You may have heard the terms “red shift” and “blue shift” which correspond to the lowering and raising of electromagnetic wave frequency as objects move away or towards the observer. Red light is the lower frequency end of the visible light spectrum, and blue the higher. The terms can apply to frequencies outside the visible spectrum as well though.
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