Investigation of the Factors Affecting the Rate at Which an Object Falls.

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Investigation of the Factors Affecting the

Rate at Which an Object Falls

Background knowledge

All objects, when no force is acting upon them, shall remain at the same steady speed, without accelerating or decelerating; so if an object is still, it shall not move and if it is moving then it shall continue moving so long as no force is acting upon them. This was explained by Newton’s first law. However it must also be noted that the meaning of “no force” may also be understood as “all forces acting upon a certain object balances each other out” so the object is in equilibrium.

    Liquids and gases are known as fluids. If an object passes through either of these two mediums there shall be a force acting in the opposite direction known as “friction”. One very important type of fluid friction is air resistance.

    If there was no force acting upon two falling objects (both having a different mass), other than gravity, they shall both fall with the same rate of acceleration regardless of their mass. This is explained by Newton’s second law which states force = mass x acceleration, so acceleration is equal to force/mass. Because the force (of gravity) is dependant upon the mass, all objects will have the same rate of acceleration. Consider the following:

          means “the force of gravity”.

This was further proved by the hammer and feather experiment on the moon where air resistance is scarce and the only force acting upon the two objects would be gravity (from the moon).

    However on earth objects of different masses will fall very differently. As an object falls, it continues to accelerate (because the force of gravity will be stronger than that of air resistance) until the force of air resistance is equal to the force of gravity (at this point acceleration will stop because f/m will equal one). This is call “terminal velocity”. When an object reaches terminal velocity it stops accelerating. The magnitude of terminal velocity depends on the weight of the falling object. For a heavy object, the terminal velocity is generally greater than a light object. This is because air resistance is proportional to the falling object's velocity squared. For an object to experience terminal velocity, air resistance must balance weight. An example that shows this phenomenon was the classic illustration of a rock and a feather being dropped simultaneously. In a vacuum with zero air resistance, these two objects will experience the same acceleration. But on the earth this is not true. Air resistance will equal weight more quickly for the feather than it would for the rock. Thus the rock would accelerate longer and experience a terminal velocity greater than the feather.

    In the early 1600s Galileo started to come up with new ideas about the link between force and motion. In a series of experiments, he rolled balls down slopes and deduced that that all falling objects light or heavy, should gain speed at the same steady rate.

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    It is said Galileo investigated the laws of motion by dropping cannon balls from the top of Pisa’s famous tower. This is almost certainly not true. However Galileo was born in Pisa, Italy (in 1564) and lectured there.

    Factors which affect the rate at which an object takes to fall to the ground:

  • Weight of the object. A heavier object will fall quicker. This is because the force of gravity will be greater on a heavier object and thus its terminal velocity will also be greater (as mentioned in the latter paragraph).
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