Why does gravity keep planets in orbit instead of pulling them straight into the Sun?
Quick Answer
Planets are moving sideways fast enough that they continually fall around the Sun rather than straight into it. Gravity bends their path into an orbit.
The Full Story
An orbit is a balance between inertia and gravity. A planet tends to move in a straight line, but the Sun’s gravity continuously pulls it inward, curving that path into an ellipse or nearly circular orbit. This idea was explained by Isaac Newton in the 17th century using his law of universal gravitation. Without enough sideways speed, a planet would fall inward; with too much, it could escape. The same physics keeps moons around planets and satellites around Earth.
Key Facts
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"Why don’t planets just fall into the Sun?"
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