How will gravity effect two objects of the same size and shape, but of different weights?

Question

And how will this be changed by things such as air friction, etc. Will the heavier object fall faster? Even though it has the exact same surface area as the lighter object?

Answer 1

Air friction has an influence on falling rates of bodies. Two objects that are exactly the same, but for that one is heavier than the other, won't fall at the same rate through air. The heavier one will fall faster, as you have said, because the force created by air friction is the same for both, but because of the greater mass, the heavier object will be subject to less negative acceleration. Recall that F = ma, and this works for negative acceleration due to the force of air resistance. The greater m is, the less a will be.

Answer 2

Okay, let's define weight first of all:

Weight is the FORCE applied by an object due to the gravitational acceleration, and is calculated from:

F = ma

where a = g (the force of acceleration due to gravity, about 9.8 m/s^2), m is the mass of the object and F is the force applied.

Importantly, if there is no atmosphere and two objects (irrespective of the size, shape or mass of the objects) are dropped from the same hight they will accelerate at the same rate towards the ground and hit the ground at the same time.

Now, include an atmosphere and something interesting happens. Firstly, lets consider objects of different size and shape (one is a small ball, one is a big cube) but EQUAL MASS. If you include an atmosphere and drop them from the same height the small ball hits the floor first. Why? Because the force if the air resistance (a reactive friction-style force) acts upwards on both objects. It is creater on the larger object because the larger object has a larger surface area.

Now, as both objects have the same mass, the force downwards due to gravity is the same (F = mg is the same). The overall downwards force is more for the smaller object because the upwards reactive force from the air resistance is less. This is why the smaller object falls faster, the downwards force (and hence terminal velocity) is greater. Yes, they accelerate the same but the smaller object stops accelerating later, so ends up moving faster.

Now, lets consider two different masses of the same size and shape. This is the one that people often get wrong!

The same equation holds true (F = mg) for the downwards force, so the two objects experience a different downwards force. The upwards force from the air resistance, however, depends only on the size and shape of an object. Notice that, as both objects are the same size and shape, this reactive force will be the same for both.

This means that, overall, the force downwards is greater for the heavier object, so its terminal velocity will be greater. Yes, the two objects will accelerate at the same rate (at first, because the reactive force of air-resistance will be negligable at first), but as the two objects get faster, the force of air resistance will increase and will, eventually, balance the force downwards (so the object reaches terminal velocity and stops accelerating). This will occur sooner for the lighter object because the force downwards is lower, so the reactive force does not need to be as great.

Do you see how this works? It is a common misconception that two identical sized objects of different mass dropped from an aeroplane high up will hit the ground at the same time but they wont! The heavier object will hit the ground first because, overall, it will travel faster.

I hope this makes more sence to you.

NOTE:

moreacidthanalkaline and DJ have both got this question wrong. scythian1950 and novangelis have both got this question right. If you are confused by my answer, just read thiers (they are more concise than mine!)

Answer 3

They will hit at the same time. They will accelerate at the same speed, and reach the same max speed. If they shapes of the objects are different, one being more aerodynamic than the other, 1 of them would hit before the other. Aerodyamics in this instance refers to how well an object counteracts the resistance of the air around it. The weight of the object is irrelevant, except for the sizes of the hole that both of the objects would leave in the ground upon impact.

Answer 4

The acceleration due to gravity is the same for all objects. The force due to gravity will be proportional to their masses (their weights). As for falling, the force of air resistance is proportional to velocity squared. As the velocity increases, the air resistance increases, but the difference between weight and air resistance will always be greater for the heavier object, so it will fall faster.

Answer 5

Gravity affects all things equally - any variation in falling speed is due to air resistance, not differing gravitational pulls.

Objects of different mass but identical size and shape will fall at identical speeds.

Answer 6

If you drop 2 bowling balls off of a roof at the exact same time. Each ball the same size and shape, but one ball weighs 10 lbs. and the other ball weighs 20 lbs. Both balls will strike the ground at the same time. The heavier object will not fall faster, they will fall at the same velocity.

As for air friction, I may be making this up but my guess is from one of Newton's laws of motion which states that every action has an equal and opposite reaction. Meaning, if the 10 lb. ball is falling down against the air with 10 lbs of downward force, then the air is pressing up against the ball with 10 lbs of upward force.

hope this helps