Physics

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Fundamental principles governing matter, energy, space, and time.

FieldNatural Science

Key Concepts

The 4th DimensionExplained By A High-School Student

Doppler Effect

The change in frequency of a wave when the source and the observer move relative to each other. When they approach, the waves get compressed and the frequency rises (higher pitch, bluer light); when they move apart, the waves stretch out and the frequency drops (lower pitch, redder light). It's why a passing siren or race car shifts from high to low pitch.

• Sound: f' = f · (v + v_observer) / (v − v_source), with v the speed of sound (~343 m/s in air) and velocities positive when moving towards each other
• Light: shows up as redshift / blueshift, used to measure how fast stars and galaxies move towards or away from us
• Applications: radar speed guns, Doppler ultrasound (blood flow), weather radar, sound design (pitch shift on passing objects, e.g. Unity/Unreal audio Doppler settings)

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