Why do heavier things fall faster than lighter things if dropped from a certain height ?related to gravitational force.

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caledon's profile pic

Posted on

Most of the time, people ask this question with the idea of a Newtonian "feather vs. bowling ball" concept in mind. Based on those terms, the typical answer is correct: two objects will fall at the same speed in a vacuum, and air resistance can appear to make an object fall slower. However, there is a surprising, but more complicated nuance to this problem.

Every action has an equal and opposite reaction. This means that, just as the Earth is exerting a gravitational force on the objects, the objects are exerting a gravitational force on the Earth. Just as much as the objects fall onto the Earth, the Earth falls onto the objects as well. It's just the fact that the Earth is so much larger and more massive that we default to viewing things from the first perspective and not the latter. Nevertheless, the gravitational force exerted on the Earth by the objects cannot be ignored.

Gravitational force is determined by the Universal Gravitation law:

`F = (GmM)/r^2`

where m and M are the two masses involved in the interaction. If we do two separate calculations, one for the mass of the lesser object, and one for the mass of the greater object, we can see that there will actually be a larger gravitational force involved with the more massive object.

This is where most people would interject that, well, yes, the larger mass needs a larger force in order to achieve the same acceleration. But reverse the frame of reference; now let's consider this from the point of view of the objects doing the pulling, instead of the Earth. Now we can see that the force exerted by the larger mass is doing more pulling than the smaller mass. The Earth will "hit" the larger mass first.

Mind you, the scale that this takes place on is smaller than we can actually measure with our current technology. However, it makes sense if you consider it in a different way; If you held a brick and the Moon at the same height and dropped them, which would hit first?

readerofbooks's profile pic

Posted on

There are two ways to answer this question. The first way is to challenge the accuracy of the question, since gravity is constant for all objects. In a windless environment, basically a vacuum, a piece of paper will fall at the same speed as a metal arrow. That sounds like a lie, but it is completely true. The second way to answer the question is by taking into consideration wind resistance. Those items that are streamlined more will fall faster, because these things are able to cut the wind. Those items that are more blunt and cannot cut the wind will move slower.

pohnpei397's profile pic

Posted on

This is not an accurate statement.  Heavier objects do not fall faster than lighter objects when they are dropped from a certain height IF there is no resistance from the air.  So, if you were in a vacuum, the two things would fall at the same rate.

The only thing that makes a heavier thing fall faster than a lighter thing in real life is the fact that heavier objects usually have more mass per surface area than do lighter things.  Because of this, the resistance from the air slows the fall of the lighter thing.

But if both objects had the same ratio of mass to surface area, they would fall at the same rate.

So, the only thing that makes a lighter thing fall more slowly is the resistance from the air.

Here is a video about common misconceptions of gravity:

mkcapen1's profile pic

Posted on

Not at all. Two objects falling from the same place despite their weight differences will hit the ground at the same time.  You can test this theory by taking a tennis ball and a golf ball and standing on a table.  Hold your arms out at the same height and drop the objects.  If your arms are held at the same height the balls will hit the ground at the same time.  The times when this would not occur is if one object is flat paper and the other object is a ball.  The paper will have more resistance because of its shape.

mohem's profile pic

Posted on

They in fact do not, but because our atmosphere consist of Gas rather than vacuum, it adds a resistive to the larger surface area thus the effective gravitational force is opposed by this resistance. Think of a paper and small rock where the paper surface area greater than the solid rock, where the rock is more aerodynamic than the paper.

crystaltu001's profile pic

Posted on

It's based on the mass of the object. If 2 different things that each weighed differently were dropped the heavier item would hit the ground first since it has more mass and the lighter things tend to float for a little bit before it actually hits the ground

zumba96's profile pic

Posted on

Based on the mass if you dropped a feather from a 500 foot height and a bowling ball from the same height of course the bowling ball would hit the ground first because the mass would create more acceleration

atyourservice's profile pic

Posted on

they drop at the exact same rate, it is just that earth has an air resistance which cause lighter things to float a little bit

aeherb3's profile pic

Posted on

This can be answered best by using the equation Force= mass x acceleration. 

Please note, that there are two environments in which there will be different answers.  In a vacuum, that is, in the absence of friction, both objects will fall at the same time. Surface area and mass become important however as we imagine this scenario on our earth.  On earth where every object experiences gravity, the two objects will fall at different rates. 

Let's imagine an elephant and a feather, both dropped from the top of a very tall building.  When you drop the objects, they are experiencing the same acceleration due to gravity, but due to their different masses, they are both exerting different amounts of "downward" force.

Elephant= 1000 kg

Feather= 1kg

Acceleration due to gravity= 9.8m/s/s``

Downward force being exerted by elephant:  F= (1000kg) x (9.8m/s/s) = 9800N

Downward force being exerted by feather: F=(1kg) x (9.8m/s/s) = 98N

The next thing you have to consider is terminal velocity- Terminal velocity is when acceleration stops (this is when the force of gravity and the force of air resistance are balanced).  The feather requires much less air resistance for it to reach terminal velocity.  The elephant requires a  great amount of air resistance to slow and come to a terminal velocity. 

You can experiment with this phenomenon by designing a parachute device- try to make one that reaches terminal velocity quickly so as to protect it's "passenger" (try to save a raw egg from cracking).  You can make your parachute with cheap household materials and experiment with different masses of your parachute device, different sizes of parachute, and different design characteristics.  Keep in mind the principals of Newton's Laws throughout your experimenting.

Happy engineering!

Sources:
nb-zhu's profile pic

Posted on

Objects that are heavier will fall faster than objects that are lighter

I did an experiment by manipulating the falling object's mass, and the results confirm this statement.

Heavier objects have a greater terminal velocity because they accelerate faster, and have a greater downwards force, meaning that the object requires a greater air resistance to reach that terminal velocity. When the object reaches terminal velocity, there is zero acceleration, so when the objects mass is increased, the terminal velocity is also increased. This means it takes longer for that object to reach its terminal velocity, and during that time it is constantly accelerating. So yes objects that are heavier do fall faster!

bishalnaskar's profile pic

Posted on

Due to the effect of gravitational force all bodies fall with the same acceleration and speed in vaccum but in some other propagating media as the force acting on the body is directly proportional to its mass and also air friction comes into play.

As a result of which the body acquiring higher momentum<as a result of higher mass as p=mv> falls quicker than the lighter body...also surface area and densities are factors on which this depends..........

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