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  • Smart Learning for All

  • Topic: Oxidation.

  • Why do papers turn yellow?

  • They really do.

  • You don't believe me?

  • Alright.

  • Then why don't you spray some oxygen on the papers?

  • See, I was correct.

  • Do you know why this happens?

  • This happens mainly because of oxidation.

  • Oxidation is a chemical process in which a substance combines with oxygen.

  • Now, paper is primarily made up of wood.

  • Wood is made up of cellulose and lignin.

  • Now, these two components which are present in paper are susceptible to oxidation.

  • When they are exposed to air, they are likely to combine with oxygen, causing the color of paper to change from white to yellow.

  • But did you know that newspapers turn yellow relatively quickly as compared to books?

  • This is because there is more lignin in newspapers than in papers made for books.

  • Lignin is more susceptible to oxidation as compared to cellulose.

  • Hence, newspapers turn yellow faster than papers of books.

  • Topic: Oxidation.

  • Why do copper vessels turn green?

  • Wow. What a beautiful copper statue.

  • Have you made it?

  • Good job.

  • But why did you use copper to make the statue?

  • It will turn green after a while.

  • No No. It will not happen immediately.

  • It will take some time.

  • Look. I had told you earlier.

  • Do you know why this happened?

  • This happened because of oxidation.

  • Do you know what oxidation is?

  • It is a process in which a substance gains oxygen.

  • When the copper statue was exposed to moisture and air for a long period of time, it started to get oxidized.

  • In the oxidation process, its color started changing to blackish brown.

  • Then eventually into green.

  • The green layer of color appeared because of a number of chemical reactions.

  • That took place when exposed to moisture and air.

  • This green layer formed is called patina.

  • No No.

  • Don't worry.

  • Patina does not damage the statue.

  • Patina is just a layer on top of the metal.

  • It protects the copper beneath from further oxidation, thus keeping the properties of copper intact.

  • Topic: Cleansing ability of Soap.

  • Why is soap ineffective in hard water?

  • Wow.

  • What a beautiful painting.

  • But look at your clothes.

  • They have become so dirty.

  • Why don't you wash them?

  • No No.

  • Don't use that water along with soap.

  • Please listen.

  • Fine, then bear the consequences.

  • See, you are not able to clean them.

  • Do you know why?

  • This is because you used hard water to clean your clothes.

  • Do you know what hard water is?

  • Hard water is the water which contains high amounts of minerals.

  • Such as calcium and magnesium, in the form of ions.

  • So, are these ions of the hard water responsible for soap to be ineffective?

  • You are right.

  • Now, to understand what actually happened, let us recall the activity.

  • Initially, you drenched your clothes in hard water and then you applied some soap.

  • When we apply soap.

  • It reacts with the calcium and magnesium ions of hard water to form insoluble precipitate called scum.

  • Scum sticks to the clothes, restricting the cleansing ability of the soap.

  • Topic: Archimedes Principle.

  • Why do we weigh less in water?

  • Hey.

  • Looks like you have gained a lot of weight.

  • Come on.

  • Let us check your weight.

  • You weigh 132 pounds.

  • Alright.

  • Don't get stressed.

  • Check your weight in water.

  • Look.

  • It is much lesser.

  • Do you know why you weighed less in water?

  • The answer to this is based on Archimedes Principle.

  • Not that principal.

  • Archimedes Principle is a fundamental truth which states that an object fully or partly immersed in a fluid.

  • Experiences an upward force called buoyant force which is equal to the weight of the fluid displaced by it.

  • It went over your head, right?

  • No worries.

  • Let me explain.

  • Gravity always pulls us downwards.

  • Hence, the weight of our body always acts downwards whether we are on ground or in water.

  • However, according to Archimedes Principle, when we are in water, we experience an upward force.

  • Buoyant force which is equal to the weight of water displaced by us.

  • This upward force cancels a portion of our weight causing us to weigh less in water.

  • Topic: Newton's Third Law of Motion.

  • Why does a swimmer push the water backward?

  • There is a hole in the boat.

  • Now, how will you reach the shore?

  • Don't worry.

  • Do as I say.

  • Jump in the water and push the water backward with your hands.

  • This will help you to move forward towards the shore.

  • No.

  • You are not pushing the water backward.

  • See.

  • You are moving forward towards the shore.

  • Do you know why you were able to move forward by pushing the water backward?

  • To understand this, you need to learn about Newton's third law of motion.

  • Newton's third law of motion states that, for every action, there is an equal and opposite reaction.

  • No.

  • Not that action.

  • Wait, let me explain.

  • When we swim, we apply force and push the water backward with the help of our hands.

  • This is action.

  • In response to this action, the water pushes us forward with an equal force.

  • This is reaction.

  • Thus, in order to move forward and swim, the swimmer pushes the water backward.

  • Topic: Convex mirror.

  • Why is a convex mirror used as a rear-view mirror?

  • Wow.

  • What an amazing car.

  • But your rear view mirror is missing.

  • No.

  • Don't use a concave mirror.

  • It will usually show you magnified images.

  • Why don't you listen to me?

  • See, I was correct.

  • Now put the convex mirror and see the result.

  • Look.

  • The image is much smaller, right?

  • Do you know what the difference between the two mirrors was?

  • If we use a concave mirror for our car, we will not be able to see the vehicles behind us properly.

  • This is because the concave mirror will magnify the object and we will see a very enlarged image.

  • Thus, we require a mirror which gives us a wider view of the vehicles behind us.

  • In this case, a convex mirror proves to be the right choice.

  • This is because a convex mirror forms a highly diminished image.

  • Thus making the traffic look much smaller.

  • As a result, we can see a large number of vehicles in a very small mirror.

  • Topic: Heat.

  • Why do woolen clothes keep us warm?

  • The night is quite cold and you have worn cotton clothes.

  • Why don't you wear some woolen clothes?

  • They will keep you warm.

  • Please listen to me.

  • Look.

  • You are shivering.

  • At least now wear some woolen clothes.

  • Now you are feeling warm, right?

  • Do you know why?

  • Wait, I will tell you.

  • Both wool and cotton are bad conductors of heat, that is, they do not conduct or transmit heat to the surrounding.

  • Then why do we feel warm only in woolen clothes?

  • This is because.

  • In woolen clothes, there are more tiny spaces as compared to that in cotton clothes.

  • Due to these extra tiny spaces, woolen clothes trap more air as compared to cotton clothes.

  • Now, since air is a bad conductor of heat.

  • Woolen clothes containing more air, do not allow much of our body heat to escape into the atmosphere.

  • Thus keeping us warm.

  • Topic: Atmospheric Refraction.

  • Why do stars seem higher than they actually are?

  • Hey.

  • That is not the actual position of the star.

  • Please listen.

  • Fine.

  • Then bear the consequences.

  • See.

  • I told you.

  • Do you know why this happens?

  • This happens because of atmospheric refraction.

  • Atmospheric refraction is the refraction or bending of light caused by the earth's atmosphere.

  • It went over your head, right?

  • No worries.

  • Let me explain it to you in detail.

  • In the earth's atmosphere, the air closer to the earth's surface is denser due to gravity.

  • But as we move higher, the air density goes on decreasing.

  • This forms different media of air.

  • The layer of air closer to the earth's surface forms the denser medium.

  • While the layer of air higher up in the sky forms the rarer medium.

  • Now, when the light of a star enters our atmosphere and passes from one medium to another.

  • Atmospheric refraction takes place and the light bends.

  • When this light reaches our eyes, our eyes trace it backward as a straight line.

  • Due to this, the light appears to come from a higher point.

  • Hence, the star seems to be higher than it actually is.

  • Topic: Gravitational Force.

  • Why do you weigh less on the moon?

  • Hey.

  • What are you doing?

  • It is not possible.

  • You cannot fly on earth.

  • Please listen.

  • Look.

  • I had warned you.

  • Now, why don't try the same activity on the moon?

  • There you will weigh much less and thus, you can fly short distances.

  • See.

  • I was correct.

  • Do you know why you weighed less on the moon?

  • To understand this, we need to first learn about weight.

  • No.

  • Not those weights.

  • Weight is the force with which an object is pulled towards the center of the earth.

  • Or any other celestial body.

  • This force is called the gravitational force.

  • Greater the gravitational force exerted by the celestial body.

  • More will be the weight of an object present on it.

  • So, does this mean that the moon exerts less gravitational force than the earth?

  • You are right.

  • But do you know why?

  • This is because gravitational force is directly proportional to the mass of an object.

  • Greater the mass, greater will be the gravitational force exerted by it and thus, more will be our weight.

  • As the moon has lesser mass than the earth.

  • It has a weaker gravitational pull and hence, we weigh less on the moon.

  • Topic: Pressure.

  • Why is it difficult to cut with a blunt knife?

  • Seems like you are hungry.

  • Why don't you have an apple?

  • No.

  • Don't use the blunt knife.

  • Use the sharp knife.

  • Looks like you want to go ahead with the blunt knife only.

  • See, you are finding it difficult to cut the apple now.

  • Now, try cutting with the sharp knife.

  • Look.

  • The apple gets cut very easily.

  • Confused, right?

  • Let me explain.

  • All this happens due to a concept called pressure.

  • What is Pressure?

  • It is the force applied per unit area.

  • That means the pressure will be directly proportional to force and inversely proportional to area.

  • Now, we applied the same amount of force on both the knives.

  • Then, why was the result different?

  • This is because the area on which the force acted was different.

  • In the case of a blunt knife, the cutting edge is thicker.

  • That means, the area is larger.

  • As a result, the force of our hand falls over a larger area of the knife, producing lesser pressure.

  • Hence, it is difficult to cut with a blunt knife.

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