Topic: Gravity. Why are planets round? Because I commanded them. You wish. Planets are round because of the force of gravity. Gravity acts as if it originates from the center of a planet and pulls each point of the planet towards it. Hence, the only way for everything on the surface to be equally close to its center is to form a round shape. However, planets are not exactly round. They are roughly spherical. This is because planets spin on their axes. Just like a spinning top, right? Absolutely. When planets spin, things near the equator tend to move away from the center due to centrifugal force, resulting in formation of an equatorial bulge. Because of this bulge, the equator of a planet becomes farther from its center than its poles, creating a roughly spherical planet. Topic: Convex lens. Can a magnifying glass burn paper? I think you have gone nuts. No. It is possible. What? But how? It is because a magnifying glass is actually a convex lens. A convex lens is thicker in the middle and thinner at the edges. Like a fish? Absolutely. This shape of the convex lens makes the parallel rays of sunlight to refract such that they converge or come together at a point. So, when they come together, do they have a party? Please listen. As the rays converge, the concentration of sunlight at that point increases, thus producing heat. This heat starts a fire which eventually causes the paper to burn. Topic: Atmospheric refraction. Why do stars twinkle? Because they blink their eyes. No. The twinkling of stars is due to atmospheric refraction. Atmospheric refraction is the bending of light caused by the earth's atmosphere. I thought atmospheric refraction is the bending of my body due to earth's atmosphere. Please listen. Earth's atmosphere is changing continuously. When the light of a star travels through space towards us, the continuously changing earth's atmosphere refracts or bends the light by different amounts and in different directions every moment. When the atmosphere refracts more starlight towards us, the star appears bright and when the atmosphere refracts less starlight, the star appears dim. In this way, the amount of starlight reaching our eyes increases and decreases causing the star to appear twinkling. Topic: Surface Tension. Why are drops spherical? Because personally, I am fond of spherical shapes as compared to squares. No. It is because of surface tension. Surface tension is the property of liquids by which surface molecules of a liquid try to hold the liquid together by acquiring minimum surface area and acting like a stretched membrane. You know what, everything just went over my head. Alright. I will explain. Inside a drop, each water molecule is pulled with a force by its neighboring molecules. As these forces are equal and opposite, they get neutralized. However, the molecule present at the surface is not attracted outwards. It is attracted only inwards and sideways. Sideways forces get neutralized. But because of the inward force, each surface molecule contracts to form a shape that has minimum surface area which is a sphere. Topic: Resonance. How does sound break glass? Obviously, using a hammer. No. It is because of resonance. I know. Resonance means to keep calm and balance. No. Wait, I will explain. Every object when struck vibrates at its natural frequency. If we make sound having a frequency which matches the object's natural frequency, then that object starts to vibrate. This phenomenon is called resonance. So, this was the reason why my legs started to move when the music system was switched on. Just listen. Every glass is made up of different materials. However, all of them have a natural resonant frequency. Hence, when we make sounds which match their resonant frequencies, the glasses start to vibrate. As glass is a brittle material, louder the sound, more violently will it vibrate causing the glass to shatter into pieces. Topic: Friction. Why is it difficult to pull a boat on the beach than on the sea? Hey. You will find it difficult to pull the boat on the beach. Pull it on the sea. There it will be quite easy. Indeed. Why not? Fine. Don't listen. I am so tired. At least now try to pull the boat on the sea. It is quite easy, right? Yeah. Do you know why? This is because of friction. Friction is the force which opposes the motion of an object. It always acts in the direction opposite to the direction of motion. The amount of friction depends upon the texture of an object and the surface on which it is being moved. Rough textures or surfaces offer greater friction as compared to smooth textures or surfaces. Do you want to say that my brand new boat has a rough texture? No. Even though the texture of the boat is almost smooth, the small particles of sand present on beach form a rough surface. Hence, when we pull the boat on beach, the sand particles offer greater friction and oppose the motion of the boat. Thus making it difficult to move the boat on beach. However, the sea being a liquid, forms a smooth surface. Hence, when we pull the boat on sea, it offers less friction, thus making it comparatively less difficult to pull the boat on sea. Topic: Auroras. Why are auroras formed? Maybe because the earth forgets to switch off the lights. No. Let me explain. Our sun is a giant burning star. It expels tons of solar wind into space. Solar wind consists of super hot charged particles which are fatal. So, should we use a big umbrella to protect ourselves from these particles? No. The earth's magnetic field acts like a shield and protects us. Its field lines appear to emerge from the south pole and merge into the north pole. Now, when the charged particles hit our magnetic field, most of them get deflected. However, some of them flow along the earth's magnetic field lines to the poles and reach our upper atmosphere. Here, these particles collide with oxygen and nitrogen. This causes them to give off various colors of light which are called auroras. Topic: Lunar Eclipse. Why does the moon turn red? To scare us. No. Moon does not have light of its own. Why? Didn't he pay the electricity bill. Please listen. Sunlight or white light is a mixture of visible colors. Now, when the sunlight falls on the moon, it reflects all these visible colors equally, making the moon to mostly appear white. However, during a lunar eclipse when the earth is exactly between the sun and the moon, the moon appears red. This happens because of the earth's atmosphere. When the sunlight coming from the sun passes through the earth's atmosphere, the earth's atmosphere scatters the colors of the sunlight having shorter wavelengths. However, red color which has the longest wavelength is least scattered. Hence, it makes its way to the moon, making it look red. Topic: Pressure. Why does popcorn pop? Because popcorn is a pop dancer. No. There are a variety of corns such as field corn, sweet corn and popcorn. However, popcorn is the only corn that pops. Why? Does it have some magical powers? No. There are three things in a popcorn seed or kernel that work together to form a perfect popcorn. Those are an impermeable shell called pericarp, right water content and starch. When we heat popcorn kernels, the water inside them forms steam and starts to expand, while the starch turns into a gel-like substance. Being enclosed, the expanding steam applies pressure on the shells. Eventually, when the shells cannot hold the pressure, they burst open releasing the steam and gel. When this gel comes in contact with air, it rapidly solidifies forming fluffy popcorn. Topic: Ignition Temperature. Why is it easier to burn dry leaves but not green leaves? Because it is easier to spell dry than green. No. It is because of ignition temperature. Ignition temperature is the lowest temperature at which a combustible substance starts burning. Now, green leaves have moisture or water in them. Wow. So, can I use them as water balloons? Please listen. Water has a property of absorbing a huge amount of heat before evaporating. Hence, when we try to burn green leaves, a large amount of heat is required to first evaporate the water. Then to reach the ignition temperature of leaves, thus not allowing the leaves to catch fire easily. However, dry leaves don't have water in them. Hence, they don't need much heat, making them burn easily.

# Why are planets spherical? plus 9 more videos.. #aumsum

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AumSum 發佈於 2019 年 4 月 15 日

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