# Have you ever wondered!

Why do we normally swing our hands while walking and why not when we carry a load in our hands?

• The center of gravity of a body depends on the distribution of mass in the body. When we walk, the movement of the legs tends to cause a shift in the center of the gravity of the body. To compensate this shift we swing our hands. When we are carrying a load in the hands, however, the effective center of gravity is lower, making it easier to maintain the balance.

How does a kingfisher catch fish?

• The kingfisher flies vertically over the position of the fish, then plunges into water at $90^\circ$ angle. The notion here is that normal incident rays do not undergo refraction, hence the fish lies exactly where it appears to be. At any other angle than$90^\circ$, the apparent location of the fish would be different from its real location.

Why does the salt become damp when kept exposed during the rainy season and not when exposed during summer season?

• In the rainy season humidity in the atmosphere is very high, then calcium chloride (CaCl) which is an impurity in the common salt, absorbs this moisture and makes the salt damp. In summer as the temperature is high, calcium chloride tends to loose moisture through the process of evaporation and the salt is left free-flowing.

More explanation/more relevant answers are welcomed! Please share if you have any.

• If you have any such question based on facts or fun or wonder, post them in the comments and enjoy the discussion. ..

Note by Sandeep Bhardwaj
5 years, 11 months ago

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Regarding why our arms swing when we walk, I propose that experiments be done with robots that sort of look like humans, but have "arms" dangling loosely on the sides. I would bet that when such robots walk like how we do, their arms will naturally start to swing like pendulums, as a consequence of the walking action, which is far from smooth. Furthermore, I say that the more likely outcome is for arms to swing in opposite cadence with our legs. When we attempt to suppress such swinging movement of our arms, we actually have to work a bit extra, and we don't like having to work any more than we have to. Ergo, we just let our dangling arms swing as we walk.

As an analogy, and to illustrate my point, an experiment has been done with two identical pendulum clocks that have been bolted onto to a common back board, so that they are clicking side by side, at some distance from each other. The only mechanical influence they have on each other is slight vibrations sent down the back board, caused by the swinging of the pendulum. Quite invariably, given enough time, the pendulums start to swing in exact synchrony, but in opposite directions. Kind of like how our arms end up doing while walking "naturally".

- 5 years, 11 months ago

That reminds me of the "pendulums placed side by side". Problem upcoming ...

Staff - 5 years, 11 months ago

A pheasant sits with the back towards the wind-flow. Think, think, think. Why? Pheasants are mostly stinking. They hide themselves under the bushes but cannot hide the stink. They know that a predator will attack from the direction after smelling them.

- 5 years, 11 months ago