Fields and signals – gravitational field, radio waves, electronics

What it shows

Three applied-physics models share one simulation. The gravitational-field model treats a satellite in a circular orbit where gravity provides the centripetal force: the field strength g = GM/r² falls with the square of the distance, the orbital speed v = √(GM/r) decreases and the period grows, reaching about 24 hours near 6.6 Earth radii, the geostationary orbit. The radio model shows how an audio signal rides on a high-frequency carrier by amplitude or frequency modulation. The electronics model shows diodes turning AC into pulsating DC and a filter capacitor smoothing the output.

How to use

Choose a topic with the tabs. In Gravitational Field, drag sideways to change the orbital radius and read g, v and T, then press Geostationary orbit. In Radio Waves, drag to change the audio frequency and use Switch to FM or Switch to AM to compare the modulated waves. In Electronics, use Switch to full-wave and Switch to half-wave to compare the two rectifier circuits, then press Add filter and watch how the ripple in the output voltage shrinks. Reset restores the starting settings of the current tab.

Parameters you can change

• Current topic 1. Gravitational field, 2. Radio wave transmission, 3. Introduction to electronics
• Satellite orbital radius 1.1–10 Earth radii
• Carrier modulation type AM (amplitude modulation), FM (frequency modulation)
• Audio signal frequency 200–2000 Hz
• Rectifier circuit Half-wave rectifier (single diode), Full-wave rectifier (four-diode bridge)
• Add a filter capacitor at the output

Questions to explore

1. Does a satellite in a low orbit move faster or slower than a geostationary satellite, and how does its period compare?
2. In AM and in FM, which property of the carrier wave carries the audio information?
3. How does the filter capacitor make the output voltage much smoother than the rectified wave alone?