Gravity

Understanding gravitational forces, orbits, and celestial mechanics

Topics

How do satellites stay in orbit?

Satellites stay in orbit by balancing two factors: their forward velocity and Earth's gravitational pull. They move fast enough horizontally that as they fall toward Earth due to gravity, Earth's curved surface curves away beneath them, creating a stable circular or elliptical path.

How does gravity affect objects?

Gravity affects objects by pulling them toward each other with a force proportional to their masses and inversely proportional to the square of the distance between them. This causes objects to accelerate, fall, and orbit.

How does gravity affect time?

Gravity affects time through time dilation, a prediction of Einstein's general theory of relativity. Time runs slower in stronger gravitational fields—clocks tick slower near massive objects like Earth compared to clocks in weaker gravitational fields or far from massive objects.

How does the moon affect tides?

The Moon affects tides through its gravitational pull on Earth's oceans. The Moon's gravity is stronger on the side of Earth facing the Moon, pulling water toward it and creating high tides. The Sun also contributes to tides.

What is escape velocity?

Escape velocity is the minimum speed an object needs to escape a planet's or moon's gravitational pull without further propulsion. For Earth, escape velocity is approximately 11.2 kilometers per second.

What is gravitational potential energy?

Gravitational potential energy is the energy an object possesses due to its position in a gravitational field. It represents the work that gravity can do on the object as it moves to a reference point, typically calculated as mgh (mass × gravitational acceleration × height) near Earth's surface.

What is the difference between mass and weight?

Mass is the amount of matter in an object (a constant property), while weight is the force of gravity acting on that mass (which varies with location). Mass is measured in kilograms and doesn't change, while weight is measured in newtons and changes with gravitational strength.

Why do comets have elliptical orbits?

Comets have elliptical orbits because they don't have enough velocity for circular orbits when they're far from the sun. Their orbits are highly elliptical due to conservation of energy and angular momentum—they move slowly when far from the sun and faster when close, following Kepler's laws of planetary motion.

Why do planets orbit the sun?

Planets orbit the Sun because the Sun's gravity pulls them inward while their forward motion carries them forward. These two forces balance, creating a stable elliptical orbit instead of planets falling into or flying away from the Sun.

Why is gravity weaker on the moon?

Gravity is weaker on the Moon because the Moon has less mass than Earth. Since gravitational force depends on mass, the Moon's smaller mass creates a gravitational field about one-sixth as strong as Earth's.