Ask a Doubt

Only those questions are foolish which are not asked

Magnetism of Earth – What’s the cause?

Sewn posted this Message: I was recently showing my grandchildren the effect on a compass needle by the magnetic field surrounding a magnet placed in opposition to the earth’s magnetic field – Magnetism 1.01 no? Their mother then asked me how is it that the earth has a magnetic field. I confidently answered that it was due to the central molten iron core of the earth acting as a magnet, and of course as we learned in Magnetism 1.1 68 years ago on of the ways of creating a magnet is a) by striking it several blows with a hammer while holding it in alignment with the earth’s N/S axis or b) heating it. In both cases this allows the atoms to move more freely and align themselves similarly with the axis. But that started me thinking: We know that heating ANYTHING applies energy to the atoms/molecules and this then causes them to display greater and more violent movement within the body of the material. If these molecules are so agitated, how can this identical phenomenon allow the molecule/atoms of the earth’s core to “settle down quietly” into a N/S configuration and remain so

What is Mass … actually?

Pranav Asked:

“Sir, What is actually mass? In my child hood I thought that mass is something which is effected on gravitation…….but later I could see that even light attracted by the gravity….Newtons laws of motion mass is something which always opposes the change in inertia…and from Einstein’s view mass is the another form of energy…… And how we can prove 2 body of different mass accelerates differently by applying same force in the absence of friction and gravity?i am very confusing help me sir… Is it my question is blunder??”


1Science is continuing to find newer things and explaining things in different manner based on different theories.

Mass, is commonly referred to as the measure of inertia. Inertia can be experienced even at places where the effect of gravity is not experienced.

To the last part of the question,

On the surface of earth all bodies of different mass have the same acceleration due to gravity.

If we consider two bodies of different masses attracting each other, the force experienced by each will be the same, but the acceleration will be different because a = F/m (greater the mass less will be the acceleration)


A google search for “what is mass” gives


noun: mass; plural noun: masses
  1. 1.
    a large body of matter with no definite shape.
    “the sun broke out from behind a mass of clouds”
    synonyms: pile, heap, stack, clump, cloud, bunch, bundle, lump; More

    • any of the main portions in a painting or drawing that each have some unity in colour, lighting, or some other quality.
      “the masterly distribution of masses”
  2. 2.
    a large number of people or objects crowded together.
    a mass of cyclists”
    synonyms: large number, abundance, profusion, multitude, group, crowd, mob,rabble, horde, barrage, throng, huddle, host, troop, army, herd, flock,drove, swarm, pack, press, crush, mountain, flood

    “a mass of cyclists”
    • a large amount of material.
      a mass of conflicting evidence”
    • informal
      a large quantity or amount of something.
      “we get masses of homework”
  3. 3.
    the majority of.
    “the mass of the people think that the problems are caused by government inefficiency”
    synonyms: majority, larger part/number, greater part/number, best/better part,major part, most, bulk, main body, preponderance, almost all, lion’s share

    “the mass of people voted against”
    • the ordinary people.
      plural noun: the masses
      “seaside towns that catered for the masses”
      synonyms: the common people, the populace, the public, the people, the multitude, the rank and file, the crowd, the commonalty, the commonality, the third estate, the plebeians; More

      antonyms: elite, oligarchy
  4. 4.
    the quantity of matter which a body contains, as measured by its acceleration under a given force or by the force exerted on it by a gravitational field.
    “stellar objects of intermediate mass”
adjective: mass
  1. 1.
    involving or affecting large numbers of people or things.
    “the film has mass appeal”
    synonyms: wholesale, universal, widespread, general, large-scale, extensive,pandemic

    “mass hysteria”
verb: mass; 3rd person present: masses; past tense: massed; past participle: massed; gerund or present participle: massing
  1. 1.
    assemble or cause to assemble into a single body or mass.
    “both countries began massing troops in the region”
    synonyms: accumulate, assemble, amass, collect, gather, gather together, draw together, join together; More

    antonyms: disperse, disband
late Middle English: from Old French masse, from Latin massa, from Greek maza ‘barley cake’; perhaps related to massein ‘knead’.

Spin, swing, seam and more

Akash Malhotra posted
Real world application, COR –> Bounce produced by pitch, for both spinners & seamers; Contact time –> grip provided by pitch, mainly for spinners

Assuming cricket ball (leather ball) to be a sphere and cricket pitch (hardened soil) to be a flat. 
1. Would it be appropriate to assume cricket pitch as elastic-plastic flat and cricket ball as elastic-perfectly plastic sphere for modelling purposes? 
2. Does there exist any relationship (empirical or physical), relating coefficient of restitution and contact time between a sphere and a flat to their respective material properties and incident velocity.

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