Earth Satellites

Earth Satellites:

Satellite: An object that orbits the sun, the earth, or some other massive body is called a satellite. Satellites are divided into two main types, one is natural and the other is man-made.  Some examples of natural satellites are planets, moons and comets. Jupiter has 67 natural satellites. The Earth has one permanent natural satellite, the Moon we know, which causes tides in the ocean. Sometimes other objects (such as asteroids) can move into temporary earth orbits and become natural satellites within a certain distance. Apart from these, there are many artificial satellites placed in orbit on the Earth, which are used for various applications of communication and data collection. As the term itself suggests, an artificial satellite is one that is placed in space by humans and follows the orbit of natural satellites. Because they have a very large field of view, they can collect data much faster than ground-based instruments. In addition, clouds, dust and other obscurations do not obstruct their view of space beyond the Earth, which allows a satellite to observe space much more effectively than with telescopes on Earth. Satellite . More than 2,500 man-made satellites currently orbit the Earth. Most of them are of Russian origin. You may be wondering why none of these satellites collide with each other because of the volume. In fact, it is quite possible. Although care is taken to guide the satellite into specific orbits so that collisions never occur, these orbits can vary in nature. Many international organizations prevent such events. However, in 2009, a pair of Russian and American satellites collided for the first time!

Satellites are launched for a specific purpose related to multiple uses such as communications, research, weather forecasting, and intelligence. When launched into space, all different types of satellites follow the same principles of physics and are governed by the same mathematical equations. There are two types of artificial satellites based on their purpose. These are geostationary satellites and polar satellites.

Types of satellites:

Geostationary satellite:

·         These satellites are placed in an orbit around 35,800 kilometers from the Earth. They rotate in the same direction as the Earth, and one revolution of such satellites equals one day on Earth (about 2 hours). This means that when viewed from Earth, these satellites appear to be in the same place all the time. Hence the name "geostationary" satellites. These satellites are used as communication satellites and in weather-based applications.  Polar Satellite:

«  Unlike geostationary satellites, polar satellites orbit the Earth in a north-south direction. They are very useful in applications that require an outdoor view of the entire globe in one day. Since the whole globe moves under them, it is easy to do. They are used in

Weather applications where weather and climate-based disasters can be predicted at short notice. They are also used as relay stations.

Polar satellite

The International Space Station (ISS) was launched in 1998. It is a habitable artificial satellite that can sometimes be seen with a clear sky. It serves as a laboratory, observatory, and landing base for potential expeditions.

The Nature of the Satellite Projectile: 

The most important thing to understand about satellites is that they are, after all, munitions. Any object that is only affected by gravity is called a satellite. Gravity is the only thing that affects a satellite after it is launched into orbit. Movement of satellites

To understand this concept clearly, let's use the example of sending a satellite from the top of Mount Newton, a hypothetical location far above the effects of air resistance. Newton was the first scientist who present the concept that if an object is launched with sufficient speed, it will begin to orbit the Earth. This object would experience a gravitational force that would try to pull it down moving horizontally tangent to the ground. If the launch velocity is less than the escape velocity, it will fall back to the ground.

 If the projectile is fired at full speed with escape velocity, it will fall into orbit outside the earth and begin to circle the earth; dashed line C represents such an object. If the object is launched at a higher speed, it will still orbit the Earth, but will now have an elliptical orbit; dashed line D represents such an object.  It may also be possible for an object to be shot at such a speed that it escapes the gravitational pull of the earth and becomes a free body; the solid line E represents such an object. Objects C and D never fall back to the ground even though they are constantly drawn to it because our earth is a round body.

All of this observation raises the very fundamental question of how much velocity is required to shoot an object out of Earth's lower atmosphere and deposit it outside, still in the gravitational field. We get the answer by observing the main aspect of the Earth, and measuring its curvature. It has been measured that for every 8,000 meters traveled along the earth's horizon, the surface drops about 5 meters. So, applying basic math, we can assume that if a bullet wants to go around the sun, it must have.

Energy from an Orbiting Satellite:

Satellites revolve around a massive central body in either circular or elliptical orbits. A satellite orbiting the Earth travels at a constant speed and fixed height in its orbit, moving at a tangential speed that allows it to fall at the same rate as the Earth's rotation. Gravitational force acts perpendicular to the direction of movement of the satellite throughout the entire trajectory.

According to the work-energy theorem, the total initial mechanical energy of a system plus the work did by some external force equals the final mechanical energy. 

For satellites,  gravity is the only external force, and since gravity is considered a conservative force, the Wext term is zero.  The equation can be simplified as follows:

In other words, the sum of the kinetic and potential energy of a system is constant, while the energy varies between kinetic and potential energy.

Analysis of a Circular Orbit:

During the rotational movement around the Earth, the satellite remains at a certain distance from the Earth's surface all the time. Since the tangential velocity is a function of the radius of the orbit, the velocity remains constant, as does the kinetic energy. Also, since the potential energy depends on the height of the object, which remains constant in this case,  the potential energy therefore remains constant at all times. Thus, the total mechanical energy, or KE PE, remains constant.  Energy from an orbiting satellite

Analysis of Elliptical Orbits

The total mechanical energy of a satellite in elliptical motion also remains constant, as in circular motion, but unlike circular motion, the energy of the satellite in elliptical motion changes form. It is known that the tangential velocity of a body orbiting the Earth is inversely proportional to the square root of its orbital radius, and the kinetic energy also decreases as the radius increases and is inversely proportional to the orbital radius. Therefore, the potential energy increases as the height of the object increases and thus increases as the radius of the orbit.

Energy from an orbiting satellite

The movement of the satellite around the Earth is considered circular. In this section, we derive the expression for kinetic energy, potential energy, and total mechanical energy along a circular path around the Earth. Energy from an orbiting satellite

The tangential velocity of a satellite orbiting the Earth can be given as follows

Energy from an Orbiting Satellite:

Where M is the mass of the earth, R is the radius of the earth, and h is the height above the earth where the object is located. 

Thus, the kinetic energy (mass m) of the satellite in a circular orbit at speed v can be written as follows

As per our assumption, the gravitational potential energy at infinity is considered to be zero, so, the potential energy at distance (R +h) from the center of the earth can be written as

The kinetic energy here is positive whereas the potential energy is negative. However, in magnitude, the kinetic energy is half the potential energy, so the total energy E is

The total energy of a circularly orbiting satellite is thus negative but twice is the magnitude of the positive kinetic energy.


Weightlessness is a term used to describe the feeling of complete or near complete weightlessness. Astronauts orbiting the Earth often experience the sensation of weightlessness. The feelings experienced by astronauts in orbit are the same as those experienced by anyone temporarily above a seat on an amusement park ride. The reasons for the feeling of weightlessness are the same in both cases.

Why do we feel burdened?

Weight is the feeling that a person experiences when his body does not touch external objects. In other words, the sensation of weightlessness occurs when all contact forces are removed. These feelings are common in free fall mode.

During free fall, the only force acting on the body is gravity. Since gravity is a non-contact force, it cannot be felt without a counter force. That's why you feel weightless when free falling.

It is important to remember that being weightless is just a feeling, not a reality that corresponds to a weightless person. Balance has little to do with weight and a lot to do with the presence and absence of contact forces.

The Elevator Test by Otis L. Evaderz

Did you know that a scale doesn't measure weight? Rather, the scale reading is a measure of the upward force exerted by the scale to balance the downward force of gravity on the person standing on the scale. When the body is in equilibrium, these two forces are in balance. The upward force on the person is equal to the downward force of gravity. In such cases, the weight reading corresponds to the person's weight. However, if the person standing on the scale jumps up and down, the scale reading changes rapidly. When bouncing, the body accelerates. As a result, the upward force of the scale changes. Does this mean the weight will also change? Of course not! You weigh the same. Only the weight reading changes, because it does not measure your weight, but the contact force acting on the body.  Otis L. Evaderz performed the famous elevator experiment by riding up and down an elevator while standing on a bathroom scale. He noticed that the reading on the scale was different when he accelerated up and down and when he was at rest or moving at a constant speed. We know that the scale reading is a measure of the upward normal force, so its value can be predicted at different stages of the movement. The value of the normal force acting on Otis' 80 kg body could be predicted if the acceleration is known. This prediction is made using Newton's second law of motion.


In the diagram, the 80 kg Otis is moving at constant speed (A), accelerates up (B), accelerates down (C), and falls freely (D) after the elevator cable breaks. The normal force is greater than gravity because the elevator is accelerating upward (B). And it is less than gravity with downward acceleration (C and D) and equal to gravity without acceleration.

Since normal is responsible for detecting weight, the lifter feels his normal weight in case A, slightly heavier in case B, and less than normal weight in case C. For D, the rider felt a weight, without an external force he would not feel the weight. Finally, it can be stated that the rider weighs the same in all four cases, but the sensation of heaviness he feels is different. The weight of the rider varies during the ride.

Why do astronauts feel weighed down in space? Astronauts orbiting in space feel weightless because there is no external contact force in space to push or pull their bodies. Gravity is the only force acting on their bodies. Gravity, which is force acting at a distance, cannot be felt and therefore does not give a sense of weight.

Do astronauts experience weightlessness because there is no gravity in space? Many students assume that astronauts feel weightless because there is no gravity in space. This is not true. If this were true, it would violate the principles of circular motion. If someone believes that the lack of gravity in space is the reason for weightlessness, should they come up with a reason for astronauts orbiting in space?

Is gravity in space less than gravity on Earth?  The gravity acting on an astronaut in space is certainly less than the gravity on the Earth's surface. But it is not small enough to account for the drastic weight. Consider a space station orbiting about

00 km above the earth when the value of g at that location decreases from 9.8 m/s2 to about 8.7 m/s2. While this certainly reduces weight, it does not account for the absolute weightlessness experienced by astronauts. Their sense of absolute weightlessness comes from the fact that they have no surface to support them as they freely fall to Earth.