Orbits and Orbital Motion — Reading Comprehension

Orbits are the curved paths that objects follow around other objects in space. Satellites, planets, and moons all move in orbits because of a balance between two forces: gravity and forward motion. Gravity pulls objects toward the center of a planet or star, while forward motion tries to carry them away in a straight line. This balance creates the continuous, curved path we call an orbit.

How Orbits Work: The Role of Gravity and Motion
Gravity is the force that pulls two objects together. Earth's gravity pulls satellites and the Moon toward its center. At the same time, these objects are moving forward at high speeds. If an object moves fast enough, gravity bends its path into a curve instead of letting it fall straight down. This is how satellites stay in orbit—they are constantly falling toward Earth but also moving forward, so they keep missing the ground. Isaac Newton explained this in his famous thought experiment called Newton's cannon. He imagined firing a cannonball horizontally from a high mountain. If the cannonball traveled fast enough, it would fall around Earth instead of into it—creating a circular orbit.

Orbital Velocity and Satellites
To stay in orbit, an object must reach a certain speed called orbital velocity. For satellites in Low Earth Orbit, this speed is about 8 kilometers per second (28,000 kilometers per hour). If a satellite goes slower, gravity will pull it down to Earth. If it goes faster, it could escape Earth's gravity completely. Satellites higher above Earth need less speed to stay in orbit because gravity is weaker farther out. There are natural satellites (like the Moon) and artificial satellites (like the International Space Station) that use these principles to orbit Earth.

Weightlessness and Microgravity
Astronauts on the International Space Station appear weightless, but gravity is still present—about 90% as strong as on Earth's surface. They float because they are in a state of freefall. The station and everything inside it are falling toward Earth, but their forward motion keeps them in orbit. This creates the sensation of microgravity, or very weak gravity. The term 'weightlessness' is not completely accurate, since gravity is still acting on the astronauts and the station.

Understanding orbits is essential for launching satellites, predicting planetary motion, and exploring space. The balance of gravity and motion not only keeps our Moon circling Earth, but also allows us to study our planet and the universe from above. The same principles explain how planets orbit the Sun and how other stars have their own planets.

Interesting Fact: 
Satellites in Low Earth Orbit travel so fast that they circle the planet once every 90 minutes!

What two main forces combine to create an orbit?

According to the passage, what is orbital velocity?

How fast must a satellite in Low Earth Orbit travel to remain in orbit?

What does 'microgravity' mean as used in the passage?

What is the main reason astronauts appear weightless in the International Space Station?

Which of the following is an artificial satellite?

True or False: Gravity is completely absent for astronauts in orbit.

True or False: A satellite moving faster than orbital velocity will escape Earth's gravity.

If a satellite slows down while in orbit, what will most likely happen?

Why do satellites in higher orbits need to move more slowly than those in low orbits?