Category: Science

There are different types of waves in this world. Every day, they affect us in one way or the other. But before we look at these different types of waves, we have to understand what a wave is.A wave is a vibration, oscillation or disturbance traveling through a medium which transfers energy from one particle in the medium to another but doesn’t displace the medium itself permanently.

Why is the study of waves important?

Waves are important to understand a variety of physical phenomena that happen around us everyday. From water waves to seismic (earthquake) waves that can cause a lot of destruction to life and property, from radio waves that form the basis of telecommunication to microwaves that help us cook food, from UV rays that can damage our skin to X-rays that have medical applications, they are everywhere.

Understanding the concept and functioning of waves can not only help us understand how various devices work, but also help us protect ourselves from the harmful effects of certain phenomena.

Types of waves

There are three major types of waves.

1.Mechanical waves

A mechanical wave is created by an oscillation or a disturbance (caused by a source) in an elastic medium (gas, liquid or solid). This disturbance causes a movement of the particles (which also gain energy) in the medium directly in contact with the source. These particles in turn transfer their energy to the nearby particles and so on. This leads to a transfer of energy and the propagation of the wave through the medium.

Example: A classical example is a stone falling into a pond or a lake. You can observe that ripples (waves) are created from the point where the stone falls into the water, moving outward. This is because, at the point where the stone touches the water, it displaces the water molecules that it directly comes in contact with. These water molecules gain energy, move and transfer the energy they gained to the nearby water molecules, which start moving. Then the nearby molecules do the same to the water molecules near them and so on. This movement of molecules creates a wave along the surface of the lake or pond.

To understand mechanical waves better, we should learn about the three types of mechanical waves and how they differ from each other.

Transverse waves

When the particles in the medium move in a direction perpendicular to the direction of movement of the wave, we call such a wave a Transverse wave.

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When you attach one end of a rope to an immovable object and move the other end of the rope up and down, the resulting wave is a transverse wave.

As you can see from the image below, while the wave is moving from left to right, the particles are just moving up and down. You can select a single particle to observe its motion.

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Examples – Vibrations in a guitar string, electromagnetic waves

Longitudinal waves

When the particles in the medium move in the same direction as the wave, the wave is called a longitudinal wave. Longitudinal waves always require a medium.

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If you attach one end of a slinky or a spring to a immovable object and push and pull the other end, the resulting wave is a longitudinal wave. In the image below, as you can see, the wave moves from left to right (the Compressions form the wave) and the particles oscillate from left to right and right to left.

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Example – Sound waves

Surface Waves

Surface waves are created when a disturbance occurs at the interface between two mediums.

Waves caused by wind on the surface of water (interface between air and water, 2 different mediums) is the most common example of surface waves. A surface wave is characterized by the circular motion of the particles in the medium and can be considered as a combination of both longitudinal and transverse waves.

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In the picture above, you can see that while the wave moves from left to right, the particles follow a circular path. At the top and bottom of the circle, the particle can be thought of moving left to right and right to left (longitudinal), whereas at the left and right side, it can be thought of moving from top to bottom and vice versa (transverse). This can also happen at the interface between 2 liquids like water and oil.

2. Electromagnetic waves

Produced by the vibration of charged particles, electromagnetic waves don’t need a medium for propagation. Therefore, they can travel through solid, liquid, gas and vacuum. Created by the interaction between electric and magnetic fields, electromagnetic waves can be further classified into different waves depending on the frequencies. They look like transverse waves (sine waves) and some of the properties of transverse waves apply to electromagnetic waves as well.

Example – X rays, UV rays, Infrared rays, visible light, etc.

You can read more about electromagnetic waves in our blog post here: 7 types of electromagnetic waves.

3. Matter waves

Till 1900 light was thought to be a combination of electromagnetic waves, whereas matter was thought of as a combination of localized particles. However, Albert Einstein proposed that light is made up of photons which can have both particle as well as wave nature.

In 1924, De Broglie proposed that similar to photons, electrons can also exhibit wave properties. Since then, it has been experimentally proven that electrons, neutral atoms and even molecules have wave-like properties.

Simply put, the wave produced by matter (like electrons, neutral atoms and molecules) is called matter wave.

Properties of a wave

Waves have some properties that define a wave.

Wavelength: Length between 2 consecutive maxima or minima

Frequency: Number of maxima or minima produced in one second

Amplitude: The magnitude of a maximum value or a minimum value

Crest: Maximum value in a transverse wave

Trough: Minimum value in a transverse wave

Compression: Most compressed part in a longitudinal wave

Rarefaction: Least compressed part in a longitudinal wave

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Facts you probably didn’t know

1. Both longitudinal and transverse waves can move through a solid. However, only longitudinal waves can travel through liquids and gases. That is how we know that the core of the earth is made of liquid (mostly molten iron). Earthquakes produce seismic waves that are both longitudinal and transverse waves. However, from the other side of the earth, a major part of the transverse waves couldn’t be detected, but most of the longitudinal waves were detected. Since transverse waves cannot move through liquids, it was deducted that the core of the earth is molten.
2. If it were not for electromagnetic waves, we would not have been alive now. Light waves, which are electromagnetic waves that don’t need a medium for propagation, from Sun made photosynthesis possible thereby creating complex life on earth.
3. The waves produced by throwing a stone into water and by blowing wind across its surface are not the same. While wind produces only surface waves along the surface, a stone thrown into water also produces (in addition to surface waves) longitudinal waves in its direction of movement, while moving to the bottom of the water body.
4. Electromagnetic waves travel at the speed of light.
5. Light travels faster than sound. That is why we see the lighting before we hear the thunder.
6. You cannot hear sounds in space because, there is no medium in space for the sound (longitudinal waves) to travel.

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This blog post lists some interesting facts about the planets of our solar system. The 8 planets in our solar system are listed in the ascending order of their distance from the Sun below.

Mercury

Mercury is a rocky planet made of a liquid metal core. The core constitutes 42% of the planet surrounded by a mantle made of silica and a solid outer crust.

Image by WikiImages from Pixabay

Venus

This planet is similar to the size and mass of our planet. However, it has a surface and atmosphere that differs from our planet considerably. Its atmosphere is extremely dense and made up of 96% Carbon dioxide and 3.5% Nitrogen.

Image by WikiImages from Pixabay

On the surface of venus, the air would be 90 times denser than that on earth. The atmospheric pressure would be equivalent to the pressure that is experienced while diving 3000 feet beneath the ocean. Due to the Green-house effect caused by Carbon dioxide, Venus is the hottest planet in our solar system. Its surface temperatures can rise up to 900°C.

Earth

Since we already know so much about the planet we live in, I skipped this section.

Mars

Mars has a rotational period and rotational axis similar to that of the Earth. Consequently, the days and seasons on Mars are similar to that of earth. It is nicknamed the `Red planet` of the solar system due to the presence of iron oxide on its surface.

Image by WikiImages from Pixabay

Mars’ atmosphere consists of almost 95% Carbo dioxide. Its atmospheric pressure is around 1% of earth’s atmospheric pressure. Therefore, liquid water cannot exist on the surface of Mars due to its low atmospheric pressure. However, its poles are covered with frozen water, which when melted can fill the surface with 11 meters of water. Mars also has 2 small moons.

Jupiter

Jupiter is one of the two gas giants in the solar system. It is composed of three-fourths of Hydrogen and almost one-fourth of Helium. Yet, its core is believed to be rocky.

Jupiter`s diameter is ten times smaller than that of the Sun, but eleven times bigger than that of the earth. Its outer atmosphere is home to several storms – the Great red spot, the biggest of these storms has been raging (at least) since the 17th century when it was first found and is almost twice as big as the earth. Jupiter also has 79 moons.

Europa

If you are looking for life in the solar system outside of earth, Europa may be your best bet. One of the biggest satellites of Jupiter, Europa is slightly smaller than our moon. However, it has all the three ingredients required to form and sustain life: liquid water, an energy source and the right organic compounds. It consists of an ice shell under which a thick layer of liquid water exists.

Saturn

The second biggest planet in our solar system and another gas giant, Saturn is also mostly made up of Hydrogen and Helium. It is famous for its rings which are formed by chunks of rock and ice. It has 62 moons. Saturn takes 10.7 hours to rotate once and 29 years to revolve around the Sun once.

Titan

The biggest moon of Saturn (which is bigger than Mercury), Titan, is the only moon in the solar system to have an atmosphere (made primarily of Nitrogen and Methane). This moon is believed to have the same conditions as early earth, since it is rich in hydrocarbons. It has liquid methane on its surface even though water and Oxygen are yet to be found.

Uranus

As the coldest planet in the solar system (-224°C), Uranus is one of the ice giants of the solar system. Although similar in composition to Jupiter and Saturn, Uranus has a layer of icy materials – water, methane and ammonia surrounding a small, rocky core. This methane is the reason for the Blue color of the Uranus. Uranus has 13 rings and 27 moons.

Image by WikiImages from Pixabay

Neptune

The only planet in the solar system not visible to the naked eye, Neptune can only be seen through a telescope. It is also known as an ice giant. Even though Uranus hits the coldest temperatures in some parts of the year, Neptune has the colder average temperature among all planets. It has 13 moons and 6 rings.

Image by WikiImages from Pixabay

Fun facts about the planets of our solar system

1. Venus is the only planets that rotates from East to West.
2. Uranus rotates on its sides, i.e., its poles are where the other planets have their equator.
3. One day on Mercury is 59 days long and one year is just 88 days long. Because of Mercury‘s elliptical orbit and sluggish rotation, the morning sun appears to rise briefly, set and then rise again in some parts of the planet. The same thing happens in reverse at sunset.
4. Neptune is the windiest world of the solar system, with winds of frozen methane traveling at 2000km/hr. The fastest winds on earth, however, hit only 400km/hr.
5. Neptune is the only planet in the solar system not visible to the naked eye.

Wait, Aren‘t there 9 planets in our solar system?

Until 1930, people believed there were only 8 planets in our solar system. However, with the discovery of Pluto on February 18, 1930, kids started learning about the nine planets of our solar system.

In the late 1990s, doubts about Pluto being a planet started to emerge.

The IAU definition of a full-fledged planet goes like this: A body that circles the sun without being some other object’s satellite, is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion, like a star) and has “cleared its neighborhood” of most other orbiting bodies.

Pluto, however, is not only small and has an offbeat orbit, but also shares its space with several asteroids in the Kuiper Belt, beyond Neptune.

Therefore, the International Astronomical Union declared Pluto as a “dwarf planet” in 2006. Thus the number of planets in our solar system was brought down to 8 once again.

We hope that these interesting facts about the planets of our solar system helped you learn about the solar system. If you liked this blog poast, you will like the following blog post too:

1. Types of satellite orbits

If you have always wondered, “How does GPS work? Does it need internet, or cell phone signal?”, this blog post will help you find out.

GPS:

GPS stands for Global Positioning System. It is a radio-navigation system consisting of 31 NAVSTAR GPS satellites orbiting at a height of 20,000 km from earth. If you remember what we learned about Satellites, you might know that GPS satellites orbit the earth in the medium-earth orbit with a semi-synchronous orbit.

These satellites are owned by USA and operated by the US Air Force. It is the process of finding a device’s (with a receiver) position on or near the surface of the earth withan accuracy of 30 cm (as of 2018). Satellites transmit radio signals (microwaves) at a frequency of 1575.42 MHz.

What are the three components of a GPS system?

The GPS system consists of a transmitter (GPS Satellite) that transmits the radio aves, a receiver (your phone) that receives the radio waves and evaluates the signals and a medium (air) through which it travels. Note that, since GPS uses microwaves (a type of electromagnetic waves), it doesn’t require a medium (gas, liquid or gas) for communication.

How does GPS work?

GPS works on the principle of trilateration. Watch this video from NASA that explains the concept of GPS and trilateration.

If you don’t want to watch the video, the same concept is explained below:

The concept is difficult to explain in 3D. So, let’s explore this in 2D. Take a look at the picture below.

Trilateration

Think of the Blue circle as the earth. Let’s say that you are standing on it at the point ‘1’. You have a cell phone with GPS (receiver) enabled and you want to find your position (to navigate to an address using Google Maps). Now, the Cell phone communicates with the satellite C, which returns the distance of the receiver from its location. Let’s draw a circle with that distance as radius and satellite C as center. Your phone (and you) can be anywhere on this Brown circle. It’s not enough to find your location though.

So, the receiver communicates with the next satellite (satellite B) and gets its distance from that satellite. So, now your phone knows its distance from these 2 satellites (B and C). It can be only in one of the 2 intersecting points ‘1’ or ‘2’, because the two circles, drawn using the distance of your phone from these satellites and these satellites as centers, meet only at these two points.

Now by knowing the distance of your phone from the third satellite, you can pinpoint the location of your phone to point ‘1’.

This concept is called Trilateration. By knowing the distance of a receiver from 3 satellites, its location in 2D can be calculated. Similarly, to find its location in 3D, 4 satellites are required. By having 24 GPS satellites, every location in earth can be tracked by 4 satellites at any given time. There are more than 5 spare satellites as well.

How does your phone differentiate between the signals from different satellites?

Each GPS satellite broadcasts a navigation message continuously at 50 bits/s. Broadcasting is a process in which a transmitter sends a message without a recipient address. All the receivers who are listening can receive this message. This navigation message consists of the following details and is 1500 bits long.

1. Time of week

2. Week number

3. Health report of the satellite (to find out if the satellite is malfunctioning)

This message is then encoded in a PRN code. All the GPS receivers know the PRN codes (sequence of zeroes and ones) of all the satellites. So, from the navigation message they receive, they can easily identify the satellite.

Facts you probably didn’t know:

1. A GPS signal doesn’t need an internet reception or telephonic reception.
2. GPS was invented due to the need for a global navigation system during the cold war and was used only for military purposes.
3. Soviet Union shot down a Korean passenger flight when it entered the Soviet airspace. This made the then American president to open the GPS for public use.
4. There are GPS shoes available, which is helpful in locating people with Alzheimer’s disease.
5. GPS can also be used to track time, since all the GPS satellites are equipped with atomic clocks.
6. If you are traveling at a height of 18,000 m faster than 1,900 km/h, your GPS device will deactivate itself so that it cannot be used as an intercontinental ballistic missile.
7. Even though US provides GPS services free of cost, US tax payers pay $3.9 million a day to keep it running.
8. Most people who have cars with GPS still use their phones for direction. – Source
9. If you use GPS a lot, beware. It reduces the ability of your brain to make mental maps as well as process spatial data. – Source

We hope that this blog post helped answer your question – “How does a GPS work?” If you liked this blog post, try our other science-related blog posts:

1. Harmful effects of electromagnetic radiation on humans
2. Planets of our solar system

What is an artificial satellite? How does an artificial satellite stay in orbit? What are the different types of satellite orbits? These are the things that you will find out by reading this blog post.

Satellites are objects or heavenly bodies that orbit a planet, star or an asteroid.

Satellites can be classified into natural satellites and man-made satellites. For example, moon is the natural satellite of earth. On the other hand, the International Space Station is a man-made satellite. In this article, the term ‘satellite’ refers to man-made satellites only.

Artificial satellites

Sputnik 1 (Russian word for satellite), the first man-made satellite, was launched by the Soviet Union in 1957. It orbited the earth once every 96 minutes. Since then, almost 80 countries have launched more than 8,900 satellites.

As of 2018 only 1,900 of these are still operational. 3,100 satellites have become nonoperational, but still remain in earth’s orbit as space debris. The rest are somewhere in the outer space.

What keeps a satellite in orbit?

As you know already, every object exerts a gravitational force on another object. The higher the mass of the object, the greater is its gravitational force. The gravitational force of the Sun keeps the planets in orbit. Similarly, the gravitational force of the earth keeps the moon and artificial satellites in orbit around the earth.

However, the gravitational force alone is not enough for an object to stay in orbit. There has to be an equal and opposite force acting on these satellites. Otherwise, they will fall on earth. This opposite force is the satellite’s momentum. It is the product of the satellite’s mass and the velocity with which it moves.

On the other hand, without gravity, these satellites will leave their orbit and travel in a straight line away from earth. So, at every point in time, the gravitational force of the earth acting on the satellite and the momentum of the satellite have to be balanced. Only then can the satellite stay in orbit.

Velocity of the Satellite and its distance from Earth

The formula for the gravitational force acting on the satellite is :

The momentum of the satellite is :Now, for the satellite to stay in orbit, its momentum and the gravitational force acting on it should be balanced. But the gravitational force acts in the vertical direction towards the earth. So, the momentum of a satellite is perpendicular (90°) to the gravitational force.Therefore, we cannot say both these forces should be equal to each other. But they should be proportional to each other, i.e., if gravitational force increases, the momentum should increase for the satellite to stay in orbit, and vice versa. We can write that as follows :Since G and mass of the earth are constant, we can write this as :The velocity of the satellite should be inversely proportional to its distance from the earth. In simple words, the closer a satellite is to earth, the higher its velocity should be, in order to stay in orbit and vice versa.

Types of Satellite Orbits

Satellites are launched into different orbits around the earth. The type of orbit a satellite takes depends on its mission. Depending on their distance from earth, satellites can be classified into the following types.

High Earth orbit

Satellites orbiting the earth at a height of 35,786 km from the surface of the earth are said to be in High earth orbit.

Satellites at this altitude are said to be in a ‘Sweet spot’ because, they are orbiting the earth with the same speed as the rotation of the earth. This means that, a satellite at this altitude looks like it is staying still. Such orbits are called Geosynchronous orbits and are used for telecommunications as well as remote-sensing applications.

If they orbit earth at any other latitude other than the Equator, they will have the same longitude. But they can move north or south (fixed longitude but changing latitude).

If a geosynchronous satellite orbits the earth directly above the Equator, it is said to be in Geostationary orbit because it appears to stay at a fixed location above earth with no change in longitude and latitude over time. This gives a constant view of the location throughout the year that makes it extremely useful for weather monitoring. The weather reports and satellite views of locations come from geostationary satellites.

Medium Earth orbit

Medium earth orbits are closer to earth than High earth orbit. There are 2 important medium earth orbits.

Semi-synchronous orbit

It is a near-circular orbit around the earth at a height of 20,200 km. Satellites in this orbit complete one orbit in 12 hours. The satellite passes over the same 2 spots on Equator everyday and another 2 spots on the Equator every night. All the GPS satellites are in this orbit.

Molniya orbit

While the semi-synchronous orbit is near-circular, this orbit is elliptical, with the earth near one edge. This helps in providing communications to high latitudes (like Canada), because these latitudes cannot be covered using Geostationary and Geosynchronous orbits.

Low earth orbit

A low earth orbit is a near-circular orbit around the earth at a height of 160 km – 2000 km with an orbital period of 128 minutes or less. The mean orbital velocity needed for a satellite to stay in this orbit is around 7.8 km/s. Most of the scientific, spy and weather satellites are in this orbit. The international space station orbits around the earth in the low earth orbit at an altitude of 400 km.

International space station

The amount of energy required to place a satellite in low earth orbit is very less compared to the other orbital regions. Therefore, most of the satellites are launched to orbit the earth in the low earth orbit. However, in the low earth orbit, the drag caused by the atmosphere damages the satellites (due to the frequent collisions between the gas molecules and the satellite) traveling at such high velocities. This process is called orbital decay. Hence, the satellites need to be re-boosted (to maintain altitude) periodically or replaced completely.

Most of the satellites in this altitude that lose functionality are made to reenter earth, where they usually burn up. Therefore, this part of the orbit is congested with space debris – around 8,500 objects larger than 10cm and a million objects bigger than 2mm.

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Polar orbit

Satellites in the low earth orbit, which pass over the Earth from pole to pole are said to be in Polar orbit. Polar orbits are at an altitude of 200 km – 1000 km. Polar orbits are normally used for earth observation, weather and reconnaissance.

By the time a satellite in a polar orbit completes one orbit, the earth would have turned a little bit. So, the satellite will now be in an adjacent time zone when compared to its last orbit. A satellite in polar orbit completes one orbit in (mostly) 90 – 100 minutes. Hence, in one day, it will see most of the earth twice.

Sun synchronous orbit

Polar orbits that are synchronous to the Sun are called Sun synchronous orbits. These orbits are at an altitude of 200 km – 600km. In a Sun synchronous orbit, regardless of when and where the satellite crosses the Equator, the local solar time is always the same. That’s why it is called Sun synchronous.

For example, whenever and wherever the NASA’s Terra satellite crosses the Equator, the local time at that moment at that place is always 10:30 am. This is important for comparing images from different years to find changes in weather, etc.

Facts you probably didn’t know

1. You can see the International space station from the ground. It is the third brightest object in the night sky. In this website from NASA, you can find how and when to spot the International Space Station from your location.
2. The first living creature that was sent into orbit was a dog named Laika (Sputnik 2, 1957 by Soviet Union).
3. A satellite has 2 main components : An antenna for sending and receiving information from earth and a power source (mostly a solar panel).
4. In 2009 an American communication satellite and a Russian communication satellite collided in space.
5. There is a satellite that has been programmed to reenter earth after 8.4 million years. It will deliver a message from us to the future civilizations.
6. Satellites can be as big as a bus (6 tons) or can be as small as a 4-inch cube (1 kg).
7. Satellites are programmed to avoid asteroids so that they don’t collide with them.

We hope this blog post helped you understand what the different types of satellite orbits are. Find out what you learned in this blog post. Take the quiz on the types of satellite orbits now.

If you liked reading this blog post on the different types of satellite orbits, you may like our following articles too.

1. Planets of our solar system
2. How does the GPS in your cell phone work?