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How was trade done earlier?

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Why are we thrown forward when brakes are applied?

  Objects fall because the mass of the Earth attracts them. The force that pulls us towards the center of the Earth is known as gravitation. It keeps us on the ground and the satellites in their orbits. This force of attraction is much less on the Moon than on the Earth-only one-sixth. For this reason, the astronauts bounce when they walk on the moon because they experience weightlessness. In the state of weightlessness, we do not feel any force of gravity and do not feel any weight. However, we feel the forces acting on us on the Earth, when we fall from a height or when we are thrown forward when brakes are applied.   What is mass, weight, and density? All objects have a mass. Because of the force of attraction on the Earth, an object has a weight. This is the force with which the body-that is, the mass of the body-is attracted. The force of gravity on the Moon is just one-sixth of that on the Earth. A person who weighs 60 kg on the Earth weighs only 10 kg on the Moon. The dens

Are Bacteria and Viruses Animals or Plants?

  How many plant species are there? Today, scientists are aware of around 320,000-500,000 different species of plants, but they estimate this number to be much higher. Many of the known trees and flowers come from Asia, while other species of plants thrive in the tropical rain forests. Some plants have adapted to live in or below water, whereas some have adapted to live in the desert areas. Algae, lichen, and moss also belong to the plant kingdom.   How do we differentiate between plant species? Earlier the scientists differentiated between plants mainly by their appearance. Today, plants are classified according to their evolution, i.e., on the basis that all members of a group must have shared a common ancestor more recently than they have with any species outside the group. Thus, the plants are broadly classified as those containing chlorophyll (the green plants) and those without chlorophyll. The green plants include the green algae and the land plants, which grow towards l

Did the earth always look as it does today?

                              No, since its origin about 4.8 billion years ago, our planet has undergone a lot of changes. The initial ball of fire cooled down and the surface slowly turned solid, today we know that the Earth’s crust is divided into several plates, which move continuously. Entire continents have been displaced and mountains, islands, and new seas have been formed or have disappeared. Even the flora and fauna have evolved over time. Many species have become extinct and new ones have been discovered. This development of the Earth over billions of years is known as the history of Earth.                           How many plates does the Earth’s crust have? The relatively sold Earth’s crust-and a part of the layer that lies below it-is divided into seven large and more than ten smaller plates. These plates float over the hot, viscous layer, which is constantly in motion- like boiling soup. These flushes of heat in the Earth’s interior are known as ‘convection cells

How Do We Determine the Approximate Date of an Event? And what is Time?

Why is it important to know about the past? Past helps us in understanding our present world in a much better way. If we know how our ancestors lived or why the wars were waged, we can understand today’s world better and get ideas for a fairer future. What appears to us as wrong today could have been right earlier. It is also interesting to know-how inventions in the past improved the lives of humans. Some major inventions that changed the way we live are metal processing that was invented around 5000 BC and the invention of the calendar, without which we cannot determine when the important events happened in the past.   How do we know about the past? Mainly the archaeologists or the historians are the people who make an attempt to find out about our past as much as they can. The historians frequently refer to various sources of history. These sources can be clay tables, grave inscriptions, or simple letters. Sometimes they have to decode the script, such as the hieroglyphs, wh

How Do We Communicate? And what is Sign Language?

  There are a lot of ways to communicate: speaking, singing clapping hooting. Even animals communicate with one another in ways different from the humans. Only humans can express their thoughts and feelings in words because of our superior brain. Both humans and animals also communicate through body language. Sometimes, we don't use words but make gestures like traffic signs or simple movements of the hand in order to communicate.   Why can humans speak, but not animals? A lot of organs such as lungs, larynx, mouth, pharynx, tongue, teeth, and brain participate in the speaking process. Although animals possess all these organs, their structure is different from that in the humans. For speaking, it is important to properly control the processes involved, mainly breathing. This is done for us by our brain. First the air is inhaled, and then deviated through to the larynx from the lungs. The larynx has small muscles called the vocal cords. When the air passes through the stretch

WHAT IS A BABY FLAP?

  Do all children have families? Earlier, most people lived in joint families. Children who had lost their parents stayed with their relative as part of their family. In today’s lifestyle, when there are fewer joint families, it is difficult for orphaned children to become part of a family. That is why there are orphanages to take care of these children, and some lucky ones are adopted and hence they find a new home. In a family the children are protected and given emotional and financial support. Apart from having a family, it is also important to have friends.     Why some parents are married and others are are not? Many couples prefer to get married, and then have children. Others do not marry, and live happily together with their children. In some cases, the parents get divorced and live separately. The children then live with one of the parents. If the parent finds a new partner, who may also have children, they often make a new family together.   What is a joint famil