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Waves in a bucket!

Arvind MR asks:

“if a drop of water is dropped in a bucket we can notice that a wave is created and it moves away as a ring……but i see that it rebounds back and come to a point again but not the starting position ……so the number no times this happens depend upon the height we drop the water droplet…..my question is why the wave rebounds after touching the ends of the bucket?”


See the animations here and try explaining yourselves

Watch an interactive animation on reflection of waves here.


Space Time

Prejith asked:

What is space time?



In order to describe an event, we need to specify its position in space and the time of occurrence. A four-dimensional continuum with the three co ordinates of space and time as the fourth co ordinate is called space-time.

The members and visitors may add more related information via comments


Can you say What’s This?

Physics of Diving

When a high diver in a swimming event springs from the board and “tucks in”, a rapid spin result. Why is this?

Answer: This is the consequence of conservation of angular momentum.

The angular momentum of a body is the product of Moment of inertia (A measure of rotational inertia and it depends on the mass as well as distribution of mass about the axis of rotation. Farther the masses, greater will be the rotational inertia) and the angular velocity (The speed of rotation)

The angular momentum of a body remains unchanged in the absence of any external torque.

When the diver dives, he is giving his body a turning and takes off with his limbs stretched. In the stretched position, the moment of inertia is more. When he “tucks in”, the moment of inertia decreases. But since this happens without any external torque, it would result in an increase in angular velocity so as to keep the angular momentum constant.

A Few Problems from Kinematics

  1. A body falling freely from rest has velocity v after it falls a height h . Calculate the distance it should fall down further for its velocity to become double
  2. A particle in uniform acceleration in a straight line has a speed of v m/s at position x meter is given by √(25-16x). What is the acceleration of the particle

Relative position of a helicopter

If a helicopter takes off from a point on earth.(at certain altitude) and its still at that point in air.After certain time interval the observer whose position was same as that of helicopter’s take off point will see the helicopter right above him.
The question arises is that how it is possible if earth is rotating hence the observer is also, but the helicopter is in air.How is it possible?
Please explain.

Big Bang Theory

‘BIG BANG’ theory is well known to all . If it actually happened, Then I thought a question about this, like as what is the actual position of our earth in the previous time of ‘BIG BANG’?? When the whole earth is like a point. … Arkajyoti asked

Explanation For Empirical Horopter: Density Of Photoreceptors

Karolis  asks: ” External SiteLink -In this website (and in many more) in page 5, it’s written that photoreceptors are more densely packed in nasal areas of retina than temporal. That’s one of the explanations why empirical horopter (that’s the unit of all points in visual field, that are seen in the same position monocularly) deviates from theoretical. In page 6, in graphs we see that the same segment in visual field has longer arc in nasal retina than temporal (binocular vision). I don’t see how these two things agree: density of photoreceptors in nasal and temporal retinas and the magnitude of arcs. If compensation would be the case, then I think it should be the reverse situation. Given there are less amount of photoreceptors in temporal area, arc should be longer than that of nasal – so that the quantity of photoreceptors in both areas would be the same.
What’s wrong with my thinking?”

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October 2020

Schrodinger’s Cat in Daily Life

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