Eli5: falling down

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So i know when an object is falling down to earth its 9.8m/s, well say a person is falling for 15 seconds and the person weighs 150 pounds would the person weight add to the speed that the person would achieve while falling to earth?

In: Physics

4 Answers

Anonymous 0 Comments

> So i know when an object is falling down to earth its 9.8m/s

That is incorrect. A falling object accelerates by 9.8m/s^2 if you ignore air resistance.

So after t seconde are t*9.8 so you get. The average speed is half the current speed so the distance you have fallen is d=t*t*9.8/2

* 1s* 9.8m/s^2 = 9.8m/s d=4.9m
* 2s* 9.8m/s^2= 19.6m/s d=19.6m
* 3s* 9.8m/s^2= 29.4m/s d=44.1m
* 4s* 9.8m/s^2= 39.2m/s d=78.4m
* 5s* 9.8m/s^2= 49m/s d=122.5m
* 6s* 9.8m/s^2= 58.8m/s d=176.4m
* …
* 15s* 9.8m/s^2= 147m/s d=1102.5m

In practice, air resistance is relevant and is proportional to the square of the speed. So a parachutist on the stomach with arms out only reaches 56m/s and head down with arms in you can reach 89m/s.
On the belly it it takes 12s to reach a terminal velocity of 56m/s and you have fallen around 450m

So a person falling for 15 s will be at or close to the terminal velocity and travel at less the 90m/s

The weight is irrelevant if you ignore air resistance so in a vacuum chamber a [feather and a bowling ball will reach the ground at the same time.](https://www.youtube.com/watch?v=E43-CfukEgs) But there is a clear difference in air.

For a human the body size scale with weight too so you have similar terminals velocity.

If you instead drop a bowling ball versus an inflated plastic ball with the same diameter the air resistance is identical but the wight differs a lot so the bowling ball have higher terminal velocity.

Anonymous 0 Comments

So, the acceleration due to gravity actually 9.8 meters per second *squared* — that is, something’s velocity increases by 9.8 meters per second every second (up to its terminal velocity).

To answer the direct question: no, a person’s weight will not significantly influence that terminal velocity. It has a lot more to do with shape and mass distribution than it does sheer mass.

Anonymous 0 Comments

>would the person weight add to the speed that the person would achieve while falling to earth?

It would probably increase his terminal velocity. That is a function of the falling object’s wind resistance and weight. If two objects fell in a vacuum so there was no wind resistance, they would fall at the same speed regardless of weight.

For the ELI5 version of why objects fall in a vacuum at the same speed, I will recount this debate as best I can in which Galileo and a rival debated over if objects of different weight fall at the same speed.

G: So you say lighter objects fall at different speed than heavier objects.

R: Most certainly so!

G: So if cracked a rock into two fragments, a big heavy one and a small light one, the heavy one will fall faster than the light one?

R: Indeed.

G: If the smaller one falls slower than the big one, what would happen to the bigger one’s fall speed if I attached the smaller one to it with a rope? Would the slower fall speed of the small one pull up on and slow the decent of the bigger rock?

R: It must be so!

G: Would these rocks tied together fall at the same speed as the rock before being split?

R: No, for both rocks are smaller than the original rock, and the smallest rock slows down the speed of the rock it is attached to.

G: Aha! but what is the difference between the two rocks tied together and the whole rock before I split it into two pieces? Aren’t all rocks collections of potentially smaller rocks held together by what bonds them? If it fell at one speed when whole, there is no reason it should fall at a different speed having been split then then tied together to make whole again. All things fall at the same speed if not for wind resistance.

Anonymous 0 Comments

The person’s weight will not affect their velocity in a vacuum. It does affect the force with which they are falling.

F = mxa = 150lbs (use metric you monster) x 9,81m/s^2.

This force will help them overcome air resistance.

This force will also affect the size of the hole that they leav eon the ground.