The Earth, Moon, and Gravity

The Earth, Moon, and Gravity

The Earth, Moon, and Gravity

Gravity A non-contact force is a push or pull that affects an object without touching it. Gravity is a non-contact force. It pulls objects toward each other. Gravity pulls everything on Earth toward Earth’s center. For example, it pulls skydivers toward the ground.

The pull of gravity depends on matter. Objects with more matter have more mass. The greater the mass, the stronger the pull of gravity. If the mass of one object doubles, the force of gravity between it and another object doubles. As the mass of the objects gets smaller, the force of gravity between them also gets smaller.

Weight is the amount that gravity pulls on an object. The Moon has less mass than Earth. The force of gravity is not as strong on the Moon. Objects weigh less on the Moon because the Moon has less gravity than Earth.

The pull of gravity also depends on distance. If objects are close together, the pull is strong. Gravity is weaker when objects are farther apart. Gravity is weaker the farther you are from the center of Earth. You weigh less on top of a mountain than you do at its base.

Revolution Moon are just two bodies in our solar system. There are seven other planets, most of which have moons as well. All planets in the solar system orbit the Sun. The Sun holds them in orbit just as Earth holds the Moon in orbit. The Sun is massive. The pull of its gravity is so strong that it controls the orbits of all eight planets, even though they are millions of miles away. Without gravity, the planets might fly off into space.

Earth rotates around the Sun. Each trip around the Sun is called a revolution. A complete revolution takes about 365 days, or one year. Seasons are caused by Earth’s tilt and movement around the Sun.

The Moon moves in an orbit around Earth. It takes about four weeks to complete one orbit. The Moon goes through phases, or shapes, during its orbit. It has craters caused by huge rocks crashing into it.

Rotation Earth is always spinning in a circle around its axis. An axis is an imaginary line between the poles. Moving around an axis is called rotation. Each day, Earth makes one rotation. This rotation makes night and day. When the part of Earth where you live faces the Sun, you have day. When it rotates away from the Sun, you have night. Earth is tilted on its axis. Earth’s tilt and its orbit around the Sun cause the seasons.