Weightlessness is a condition when your body is in free fall and the acceleration is downward at gravity. This condition can be defined by the term zero gravity. So weightlessness occurs when there is zero support of force on our body. Let us learn more about weightlessness.

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Weightlessness is a situation in which the gravitational force is 0. We feel weight because the ground exerts an equal and opposite force on our body after our body exerts a force on the ground due to gravitational attraction.


Now, when falling freely under g, there is no solid thing which can exert a force on us, which thus makes us feel to be having weightlessness. In general, the ground exerts equal and opposite force on you and hence you feel the weight, and in the same way, if you fall freely we feel being weightless.

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Weight of Object on the Moon

Let us suppose there is an object whose weight on the earth is 10 newtons.  So how much do you think the weight of the same object varies on the moon.  The force with which the moon attracts the object is the weight of the object. We know that mass of the moon is less than the mass of the earth.  Let the mass of the object be”m”,

  • Weight of the object on the moon is denoted by Wm
  • Mass of the moon is Mm
  • Radius of the moon is Rm

mmoon < mearth

Wm  <  We

Weight of the object on the moon is m × gm (acceleration due to gravity on the moon) = m × \( \frac{GM_m}{R_m ^2} \)

Weight of the object on the earth is \( \frac{GM_m}{R_e ^2} \)    or    \( \frac{- GM_e} {R_e + h}\)

  • Mass of the earth = 6 ×1024 kg
  • Mass of the moon = 7.63 × 1027 Kg
  • Radius of the Earth = 6.63  ×  10m
  • Radius of the moon = 1. 74  × 10m

Putting these values into the equation we get, \( \frac{w_m}{w_e} \) = \( \frac{1}{6} \)

Or, Wm = \( \frac{1}{6} \) We

So if the weight of the object on the earth is 10 Newton, the weight on the moon will be 10/6.

Solved Questions for You

Q1. If a rock is brought from the surface of the moon,

  1. mass will change
  2. weight will change not mass
  3. both mass and weight will change
  4. its mass and weight both remains same

Ans: B. Mass will remain same but its weight W = mg, as the rock is brought from the moon, the gravity will change so the weight will also change.

Q2. A man weighs 75kg on the surface of the earth. His weight in a geostationary satellite is:

  1. infinity
  2. 150kg
  3. zero
  4. 75/2 kg

Ans: C. A satellite revolves around the earth with the same time period of earth’s rotation that is 24 hours. Since it revolves with the same speed, the relative velocity is zero with respect to the earth hence anybody inside geostationary satellite doesn’t feel the gravity. So here the weight would be equal to zero.

Q3. A person sitting in a chair in a satellite feels weightless because

  1. the earth does not attract the object in the satellite.
  2. normal force by the chair of the person balances the earth’s attraction.
  3. the normal force is zero
  4. person in the satellite is not accelerated.

Answer: C. As the person sits on the chair, he experiences two forces. One is the gravitational force and other is the force of the chair. This is due to this normal force the person sitting in a chair in a satellite feels weightless.

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2 responses to “Kepler’s Law of Planetary Motions – Orbits, Areas, Periods”

  1. Sahil says:

    When earth is near know it move faster some gravity of earth act on it and it produce restriction so speed may be slownear sun

  2. Sahil says:

    When earth is near the sun how it move faster some gravity of sun act on it and it produce restriction and speed may be slow down

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