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  • 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.

Topic: Gravity.

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B2 US popcorn boat surface atmosphere earth atmosphere friction

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

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    AumSum posted on 2019/04/15
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