hello

when i drop two objects of different masses which object should reach the ground first , why? and why do some objects(even though they are of different masses) reach the ground at the same rate .

If we consider galileo's explanation: "all objects accelerate at the same rate (ignoring air resistance)".

im really confused!
plz help!

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Reply 1

shawn_o1

air resistance of course

Reply 2

me2*

i know that , but what does air resistance do to a heavier object compared to a lighter object,
why does a heavier object reach the ground first(when there is an air resistance)?

Reply 3

Stonebridge

Original post by me2*

i know that , but what does air resistance do to a heavier object compared to a lighter object,
why does a heavier object reach the ground first(when there is an air resistance)?

If the heavier and lighter objects are roughly the same size then the air resistance force on them will be roughly the same.
So let's imagine the heavier object is 1000N and the lighter object 100N in weight. (Weight (mg) is a force, remember. 1st object mass 100kg and second object mass 10kg and g=10m/s/s)
Let's also imagine as they fall the resistive force at some point is the same on both, as they are both roughly the same shape and size. (You have to compare like with like for it to be meaningful.) Let's say the air resistance force is 50N

So the resultant downwards force on the heavier object is
1000N - 50N (weight down minus friction opposing)
=950N

The resultant downwards force on the lighter object is
100N - 50N
=50N

So, using F=ma to find the downwards acceleration a=F/m
Object 1
a = 950N/100kg
Object 2
a = 50N/10kg

Which of the two, taking the air resistance into account, has the greater downwards acceleration.

Reply 4

Krushems

It depends on their surface areas - how aerodynamic they are

Reply 5

me2*

Original post by Stonebridge

object A right?

Reply 6

Stonebridge

Original post by me2*

object A right?

Yes, because, in simpler terms, if the air resistance is roughly the same for both, it has less of an effect (proportionally) on a heavier object than a lighter one. The lighter object's downwards acceleration is reduced more than the heavier.
Without air resistance, they both have the same downwards acceleration. (Try putting the resistance force = zero in my example)

Reply 7

me2*

Original post by Stonebridge

youre assuming they are falling at terminal velocity so that means that at terminal velocity the friction/drag for both objects is equal? am i right?

Reply 8

SK7866

Quite a eye catching title.

Hello ------- Physics

Reply 9

Stonebridge

Original post by me2*

youre assuming they are falling at terminal velocity so that means that at terminal velocity the friction/drag for both objects is equal? am i right?

No I didn't assume that. I said that the forces were those "at some point".
I was talking about acceleration and F=ma. It was at some point where the weight of the object is still greater than the resistive force and there is a resultant downwards force and acceleration.
At terminal velocity the resistive force has grown so large (it increases with the speed of the falling object) that it now equals the weight.
In this case the resultant force is zero and there is no acceleration. The object falls at constant speed. Terminal velocity.