The way we perceive waves, like sound, can change based on how fast the source of the waves is moving compared to us. This change is known as the Doppler Effect.

Understanding the Doppler Effect

1. Moving Towards Us:
   When the wave source, like a car or an ambulance, moves closer to us, the waves get squeezed together. This makes the sound seem higher in pitch.

   Here’s a simple way to think about it:

   • Imagine an ambulance that makes sound waves. If it is moving towards you, the formula to find the new sound (frequency) we hear is: $f' = f \left(\frac{v + v_o}{v - v_s}\right)$
   • In this formula:
     • f = how fast the source normally makes waves.
     • v = the speed of the waves.
     • v_o = how fast we are moving toward the source.
     • v_s = how fast the source is moving toward us.

2. Moving Away From Us:
   On the other hand, when the wave source moves away from us, the waves stretch out. This makes the sound seem lower in pitch.

   The formula for this situation looks like this: $f' = f \left(\frac{v - v_o}{v + v_s}\right)$

Real-Life Example

Think about an ambulance with its siren on. When it is moving toward you at 10 meters per second and makes a sound at 1000 Hz, the sound seems louder and higher in pitch.

But then, as it drives away, the sound grows quieter and lower in pitch. This clearly shows how the Doppler Effect works in real life!