A siren stands still while a cyclist rides straight towards it. What frequency does the cyclist measure?

1. Frequency measured by an observer is the number of complete wave cycles that pass in each second. 2. A cyclist riding towards the siren runs into crests that would otherwise have taken longer to arrive. 3. More complete cycles therefore pass the cyclist each second than pass a still listener. 4. So the measured frequency is higher than the frequency the siren emits. 5. It cannot stay equal, since equality happens only when there is no relative motion between source and observer. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 6: Doppler effect_