Physics, visually · Waves, Sound & Light · Concept 08
Wave Properties
How does a wave travel across a pond without the water going anywhere, and how are sound and light waves different?
A wave carries energy, not matter. Change its frequency and wavelength and watch the speed that comes out.
- Transverse tab. Watch the red dot: it only moves up and down while the wave runs to the right.
- Double the frequency without touching the wavelength. What happens to the wave speed?
- Sound tab. The particles move back and forth along the direction of travel, bunching into compressions and spreading into rarefactions.
Speed = how often × how long: v = f λ.
Wavelength λ is the length of one full wave. Frequency f is how many waves pass each second (hertz). Amplitude is the height, which is the energy. Wave speed is simply f times λ.
Ultrasonic sensors
A sensor sends a 40 kHz sound pulse and measures the echo time. Distance = speed × time / 2, so v = f λ helps pick the frequency for good resolution.
Vibration on rotating machines
A motor shaft shaking at its turning frequency makes waves in the frame. Measuring f points to the cause: unbalance, bearing, or belt.
Radio and Wi-Fi
Electromagnetic waves travel at 3 × 108 m/s. At 2.4 GHz the wavelength is about 12.5 cm, which sets the antenna size.