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Satellites: Falling Around the Earth
A satellite stays in orbit because it is falling freely towards the Earth while moving sideways so fast that the ground curves away beneath it. Imagine throwing a stone harder and harder from a tall tower: it lands farther each time, and at about 8 kilometres per second it never lands at all, because the Earth's curve drops away as quickly as the stone falls. Gravity supplies the centripetal force that bends the path into a circle or ellipse. This is why astronauts inside a satellite float: they and the craft fall together, so there is no push between them. Gravity there is still strong, nearly the same as on the ground. Exams love this idea, because a student who thinks 'no gravity in space' loses marks. These cards cover orbital speed, Kepler's laws, the two orbit types and ISRO rockets.
1. Why do astronauts in an orbiting satellite appear weightless?
2. The orbital speed of a satellite close to the Earth's surface is about:
3. A geostationary satellite has an orbital period of:
4. Which of Kepler's laws states that a planet moves fastest when it is nearest the Sun?
5. Satellite A orbits at radius r and satellite B at radius 4r around the same planet. How do their orbital periods compare (T_B : T_A)?
6. Which Indian launch vehicle is mainly used to place satellites in polar and sun-synchronous orbits?
7. Two satellites of masses m and 3m move in circular orbits at the same height around the Earth. Their orbital speeds are in the ratio:
8. India's first satellite, Aryabhata, was launched in: