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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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
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