GRAVITATION-QnA

Q1: How would you define gravitation?

Gravitation is the natural force that makes any two objects in the universe pull each other towards themselves.

Q2: What is meant by the universal law of gravitation?

This law states that every object in the universe pulls on every other object, with a force that increases with their masses and decreases as they move farther apart.

Q3: What is the mathematical expression for gravitational force?

The gravitational force is calculated using \(F = G \frac{m_1 m_2}{r^2}\), wherem \(m_1\) and \(m_2\) are the masses andrrris their separation.

Q4: State the value and SI unit of the gravitational constant.

The constant \(\mathrm{G}\) is valued at \(6.67 \times 10^{-11}\,Nm^2/kg^2\)

Q5: What does it mean when an object is in free fall?

An object is said to be in free fall if it is moving towards the Earth's surface under the sole influence of gravity.

Q6: What is acceleration due to gravity?

Acceleration due to gravity \(g\) is the rate at which an object's velocity changes as it falls solely under the force of gravity.

Q7: Quote the typical value ofgggnear Earth's surface.

Near the Earth's surface, \(g\) is generally taken as \(9.8m/s^2\).

Q8: Define mass.

Mass refers to the measure of matter present in an object, unchanged by location.

Q9: Define weight.

Weight is the force with which Earth attracts a body towards its center, dependent on mass and gravity.

Q10: Name the SI units of mass and weight.

The SI unit of mass is kilogram (kg) and that of weight is newton (N).

Q11: Why do some objects sink while others float in water?

Objects with greater density than water sink; those with lower density float.

Q12: What is buoyant force?

Buoyant force is the upward push exerted by a liquid on any immersed object.

Q13: How is density defined?

Density is calculated as mass divided by volume, showing how tightly matter is packed.

Q14: Give the SI unit for density.

Density’s SI unit is kilograms per cubic meter \(kg/m^3\).

Q15: What does relative density indicate?

Relative density compares a substance's density to that of water, with no units.

Q1: List factors that change gravitational force between objects.

Gravitational force depends directly on the product of the objects’ masses and inversely on the square of the distance separating them.

Q2: Why does acceleration due to gravity \('g'\) not have the same value everywhere on Earth?

The value of 'g' slightly changes due to Earth's irregular shape and the effect of its rotation, making it greater at the poles than at the equator.

Q3: Distinguish between mass and weight.

Mass remains unchanged regardless of location, but weight changes with the gravitational pull; mass is measured in kilograms, weight in newtons.

Q4: Explain why a feather and a stone fall at the same rate in a vacuum.

There’s no air resistance in a vacuum, so every object falls with the same accelerationas as acceleration due to gravity acts same across all objects. Mass of object does not matter.

Q5: What is meant by weightlessness?

We experience weightlessness whenever we're falling freely under gravity and nothing is holding us up.

Q6: Why does an object seem to weigh less when immersed in water?

Water exerts a buoyant force upward, which partly balances the object's weight, making it seem lighter.

Q7: What is the significance of the universal gravitational constant (G)?

\(G\) determines the strength of gravity in Newton’s law, acting as a proportionality constant valid everywhere in the universe.

Q8: Write the equation relating height and time for an object in free fall.

The height \(h\) fallen in time \(t\) under gravity \(g\) is \(h= \frac{1}{2} g t^2\).

Q9: Why is \(g\) taken as negative during upward motion?

\(g\) opposes upward motion; thus, when an object is thrown up, the acceleration due to gravity is negative relative to its initial direction.

Q10: What can you infer about an object’s density if it floats on water?

The object’s density is less than that of water if it floats.

Q1: Derive the formula for an object’s weight on Earth.

Weight \(W\) equals mass \(m\) times acceleration due to gravity \(g\); thus, \(W = m \times g\).

Q2: State and illustrate Archimedes’ principle.

Archimedes’ principle says a body immersed in a fluid is buoyed up by a force equal to the fluid’s weight displaced. For example, ships float by displacing water equal to their own weight.

Q3: If a wooden block floats in water with 60% submerged, determine its relative density.

Since the submerged volume fraction is 0.6, the block’s relative density is also 0.6 (60%).

Q4: Explain why we feel lighter in a swimming pool.

The upward thrust (buoyant force) provided by water lessens the apparent weight felt by the body while swimming, resulting in a feeling of lightness.

Q5: State Newton’s law of gravitation and mention a real-world example.

Newton’s law asserts that every two masses attract each other with a force:\(F=G \frac{m_1 m_2}{r^2}\). Example: This explains moon’s orbit around Earth.

Q1: List some everyday phenomena explained by gravitation.

Phenomena like falling rain, tidal movement, holding our atmosphere, and satellite orbits are all results of gravitational force at work.

Q2: Explain the difference between mass and weight, illustrating with diagrams.

Mass (measured by a beam balance) does not vary from place to place, but weight (measured by a spring balance) changes as gravity changes. Diagrams can show this: beam balance measures mass; spring balance measures weight.

Q3: Discuss causes and effects of free fall in detail.

Free fall is caused by gravity acting alone on a body. Effects include acceleration towards the ground, sense of weightlessness, and, in extreme cases, astronauts floating in spacecraft.

Q4: Why is gravity stronger at the poles than at the equator?

The Earth’s shape (flattened at the poles) and its spinning cause gravity to be greatest at the poles and least at the equator; this also causes variations in felt weight around the globe.

Q5: Explain, with daily examples, how Archimedes’ principle helps us understand floating and sinking.

Archimedes’ principle explains why things like logs or boats float (by displacing water), why hot air balloons rise, and even why we feel lighter under water or in a swimming pool. Precise calculations show the upthrust equals the weight of fluid displaced.

Q1: State the universal law of gravitation.

The universal law of gravitation states that every mass in the universe attracts every other mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

Q2: Write the formula to find the magnitude of the gravitational force between the earth and an object on the surface of the earth.

The formula to calculate the gravitational force between the Earth and an object on its surface is: \[F=G\frac{Mm}{R^2}\] Where, \(G \) is the universal gravitational constant
\(M\) is the mass of the Earth
\(m\) is the mass of the object
\(R\) is the radius of Earth

Q3: What do you mean by free fall?

Free fall describes the motion of any object that is dropping towards the ground under the sole influence of gravity, without any force from air resistance or anything else slowing it down. In this situation, gravity is the only reason the object speeds up as it falls, and nothing else is affecting its path.

Q4: What do you mean by acceleration due to gravity?

Acceleration due to gravity refers to how quickly an object’s speed increases as it falls toward the Earth, solely because of Earth's gravitational pull. It is a fixed rate for all freely falling objects near the ground, no matter what their mass is.

Q5: What are the differences between the mass of an object and its weight?

Q6: Why is the weight of an object on the moon 1/6 th its weight on the earth?

The reason an object weighs only one-sixth on the moon as compared to the Earth is because the moon’s gravity is much weaker. The moon is smaller and less massive, so it doesn’t pull as strongly on things. If you were to stand on the moon and step onto a weighing scale, it would show a value that is just a fraction—exactly one-sixth—of what you see on Earth. Your body hasn’t changed, but the force pulling you down is much less on the moon because of its lower gravity.
See Derivation

Q7: Why is it difficult to hold a school bag having a strap made of a thin and strong string?

It’s harder to carry a school bag with a strap made from a thin and tough string because all the weight presses down on a small area. That tiny string pinch sharply into your shoulder, making it uncomfortable and sometimes even painful, as the force is concentrated in one spot rather than spread out. If the strap were wide, the pressure would be shared over a bigger patch, and you’d feel much less discomfort carrying the same load.

Q8: What do you mean by buoyancy?

Buoyancy is the gentle lift that we feel when we try to push something down into water or any other liquid.
It’s the force that fluids apply upward on objects, making them seem lighter or even float.
This upward push is why boats can stay on the surface, and why carrying something underwater often feels much easier than lifting it in air.

Q9: Why does an object float or sink when placed on the surface of water?

Whether an object floats or sinks in water comes down to how its density compares to the water’s.
If the object is lighter for its size than water, the upward push from the liquid is strong enough to hold it up, so it floats.
But if the object is heavier for its size—that is, its density is more—the water can’t support the extra weight, and the object sinks down.
It’s all about which force wins: gravity pulling it down or buoyancy pushing it up.