Do heavier objects fall faster than lighter objects?
This is part of a series on common misconceptions.
Is this true or false?
Heavier objects fall faster than lighter objects.
Why some people say it's true: If a feather and an egg are dropped, then the egg will reach the ground first.
Why some people say it's false: Acceleration due to gravity is independent of the mass of the object.
The statement is \( \color{red}{\textbf{false}}\).
Explanation:
The above statement is not true in all situations. It is true that if from the top of a building, a feather and an egg are dropped then the egg will win the race. To understand why feather lost, let's think about the forces. During the fall, there are two forces acting on the body. One of the forces is the gravitational force, which depends on the mass of the object. The other force is air resistance which depends on the surface area of the objects. The net acceleration of an object is thus given by, \[a = g - \frac{{{f_{air\,drag}}}}{M}.\] Here \(g\) is acceleration due to gravity, \({{f_{air\,drag}}}\) is the air resistance, \(M\) is the mass of the object, and \(a\) is the acceleration of the object. It can be seen from the above equation that the larger the mass the greater the acceleration and the air drag will have lesser effects. Therefore, feather loses due to the air drag.
What if the air resistance is not present? Which one will win the race this time? In the above equation if \(f\) is put equal to zero, then the acceleration of the object equals acceleration due to gravity \(g.\) This acceleration is independent of the mass of the object, and thus both the feather and the egg will fall with the same acceleration and reach the ground at the same time.
Query: What will happen if the air drag acting on the objects is different?
Reply: Air drag depends on the surface area and the speed of the object. It can be different, but the mass of the egg is much higher than a feather, which overpowers the effects of the difference in air drag. At the start when the speed is negligible, the air drag on the feather is greater as it has a larger surface area.
Query: What will be the effects of buoyancy of air that acts on the objects?
Reply: Yes, buoyancy of air acts on objects. But air has a very less density, and therefore the buoyancy effects of air can be neglected.
Suppose Galileo dropped a one-kilogram ball of cotton and one-kilogram ball of iron from the top of the Leaning Tower of PIsa, then which one will reach the ground first?
Assume that the cotton ball is tightly wadded up and that initially the bottoms of the cotton ball and iron ball are at the same horizontal level.
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