What Are Gravitational Forces Like?: Whenever an object is dropped from a distan

Question

What Are Gravitational Forces Like?: Whenever an object is dropped from a distance very near the surface of the Earth, it speeds up in a downward direction with an acceleration of magnitude 9.8 m/s2 . Two students have come up with different explanations for this phenomenon:

Kasi argues: “An object tends to move with a velocity that is proportional to the force on it and when an object falls there must be a gravitational force on it. This gravitational force in the downward direction gets larger and larger as the object falls and gets closer to the Earth. This causes the velocity to get larger and larger as the object falls, so the object undergoes a constant acceleration because the force gets larger at a constant rate as the object falls.

Heather argues: “An object tends to move with an acceleration that is proportional to the force on it. Since all falling objects accelerate at a constant rate, there must be a special gravitational force attracting it toward the center of the Earth that is essentially constant near the surface of the Earth.

Do you agree with Kasi or with Heather?

Which argument is invalid?

What observations have you made that would support your opinion?

Explanation / Answer

Heather is correct.

Gravutational force near the earth surface is constant,

Fg = mg

where g is acc. due to gravity and m is mass of object.

from newton 's second law ( Fnet = ma) , mass experience accelartion due to forrce.

Fnet = ma

force is propotional to acc.

ma = mg

a = g . ...body in case of free fall feel acc. equal to g = 9.1m/s^2.

with time as this relation , V = u + at

v - u = gt

speed increase equals to g every second.

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