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Satellite Motion

Satellite Motion

This lesson aligns with Next Generation Science Standards (NGSS) PS2.B

We use rockets to launch satellites and spacecrafts into space by loading them with enough fuel. First, we need to know how rockets lift off. The tons of propellants give the rocket enough energy to overcome the earth’s gravity and lift off into space. Newton’s third law of motion, which states that every action has a reaction that is equal in magnitude and opposite in direction, is an important idea behind the working of rockets. They burn fuel and push out the exhaust gases from a rocket’s engine down to the ground. This is the action force. In response, the gases push upward on the rocket and it lifts off the ground. In this article, we will learn about satellites, circular motion, and satellite motion.

An object orbiting around the sun, earth, or any other object is known as a satellite. Our earth is a satellite as it orbits around the sun. There are two types of division when it comes to satellites, one is natural and the other is a man-made or artificial satellite. Examples of natural satellites include the moon, planets, and comets. Our earth has many artificial satellites that are designed for various applications such as communications, military intelligence, forecasting the weather, etc.

Fig.1 it is a NISAR satellite which is used to observe natural process on earth.

Role of Circular Motion
Artificial satellite revolves around the earth in an almost circular path. An object moving in a circular path is continuously changing its direction so it is constantly accelerating. Consequently, an unbalanced force must act on the object that causes the object to keep it moving along a circular path. This force is known as centripetal force. The direction of a centripetal force is perpendicular to the direction of the object at any given point. For artificial satellites, gravity acts as a centripetal force and pulls the satellite toward the center of the earth.

Satellite Motion
Rockets are used to launch a satellite into space, when they get a specific distance from earth, they release the satellite. Once launched into the orbit, the only force that acts upon the satellite is gravity which pulls the satellite towards the center of the earth. The fundamental principle about the motion of a satellite is that the satellite is a projectile. But satellites don’t fall to the earth instead they fall around the earth because they have greater horizontal velocity as compared to a ball.

Newton was the first who theorizes that if a ball is thrown with sufficient speed, it would orbit the earth. Recalling projectile motion, if we throw a ball in a horizontal direction, the ball follows the curve path toward the ground and the horizontal and vertical motions act on it. If we throw the ball faster, it will cover more distance before falling to the ground. The faster you throw the ball, the farther it will fall from you.

Fig.2 If a ball is thrown in horizontal direction, it makes trajectory of a projectile.

Consider a cannonball launched at a small speed from the top of the legendary Newton’s Mountain, it will eventually fall to the ground. If a cannonball is launched with sufficient speed, look at the point D in the figure, it would land on the ground at the same rate as the earth curves. This would make the cannonball stay at a certain height and orbit in a circular path. Now, the cannonball falls around the earth in a circle instead of falling to the ground.

Fig.3 if a cannonball is launched at certain speed, the path of the ball would match the curve of earth, it would fall around the earth.

Similarly, a satellite in the orbit around the earth, is falling towards the earth, as the earth curves, it never reaches the earth.  A satellite continues to move ahead around the earth due to its inertia, this is because it does not require fuel to move. In the meantime, gravity continuously acts on the satellite and changes its direction. An object must be thrown with a speed of 8000 m/s to make it orbit around the earth. 

  • A satellite is any object that orbits around the sun, earth, or any other massive body.  
  • Rockets are used to launch satellites into the space by loading them with enough fuel. Rockets work on the principle of Newton’s third law of motion.
  • When a projectile is launched with greater speed, the path of the projectile would match the curve of the earth. Thus; it would not fall to the ground instead it would orbit around the earth.
  • A satellite’s motion is based on the motion of the projectile. This is because a satellite continuously revolves around the earth and never falls to the earth.

  1. Figure 1
  2. Figure 2
  3. Figure 3

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