How stuff works--4

[ws23rt]

Since there are way too many chargers laying around rusting away I thought a couple may be put to good use.

An imaginary experiment for thinking about an old law about gravity.

So two chargers are hanging suspended lets say 100ft up.  The difference between the two is the drive train is missing from one of them.

We know that when they are cut loose they will strike the ground at the same time.

The question is why?  The one that has the engine and trans is hundreds of pounds heaver than the other.  The pull of gravity pulls harder on it by that amount.

BTW if one of them was a daytona it would hit the ground first.  So the air is not part of this. 

[XH29N0G]

Think I need a whiskey to help me think about this 

[ws23rt]

It may help---

[XH29N0G]

It may help---

Thanks for posting this.  It is not something I  ever thought about, but I think I learned something.

I'll stick around sipping to see if it is right or wrong. 

[Ram07]

Isn't that like asking what's gonna hit the ground first....a ton of feathers, or a tone of bricks?

[ws23rt]

A ton of feathers and a ton of bricks weigh the same.  Ignoring the influence of air they are the same thing.

In this case the weights are different but they still hit the ground at the same time.

[Ram07]

once in free fall...isn't everything the same?

[ws23rt]

once in free fall...isn't everything the same?

The question is why do different weights fall at the same rate?

[Ram07]

wouldn't it depend on what height they were falling from?

[ws23rt]

No

[Ram07]

 ...dammit....I almost remember this....guess using the google machine is cheating, right?

[XH29N0G]

I find all this talk about dropping chargers a little disturbing.  Why not leave the chargers out of it and save em for  .  Couldn't we instead drop a ricer and dump truck?   

[ws23rt]

Hey---just trying to include chargers that are rusting away.
BTW all the wrinkles can be fixed. And in our minds it is cheap.

[Fred]

once in free fall...isn't everything the same?

The question is why do different weights fall at the same rate?

I'm guessing there's a severe down draught.   

[Chargerguy74]

The acceleration due to gravity is a constant 9.81 meters per second per second. So lets say in a void, excluding all drag, wind resistance etc. both cars would accelerate towards the earth at the same rate from a speed (or velocity if you will, since we have direction) of zero at the time of release and would impact the earth at the same time. The difference in mass of the objects will have no bearing on the acceleration imparted by the Earth's gravity. Obviously the car with the greater mass will have more kinetic energy at impact and hit the earth with more force since force is mass x acceleration.

[XH29N0G]

I think ws23RT was asking why weight/mass causes no change with acceleration due to gravity, but it sure has a lot to do with acceleration when we use the wheels of our cars.

I'm also waiting for the answer.  I have an idea that I want to check, but I don't want to spoil the fun it if it is right.

[ws23rt]

You have described what is taking place in the example and it is indeed true.
Both cars will accelerate toward the ground at the same rate.
It is true that the difference in the mass of the objects will not make a difference and that is why they hit the ground at the same time.
The question is why do they both accelerate at the same rate---

As XH pointed out---When we accelerate our cars there is a real difference in the amount of energy required to move a heavy car vs a light car

[Chargerguy74]

So basically, you're asking why gravity behaves the way it does?

[ws23rt]

No ---This is just an exercise in how the world we live in works.  We all know the answer because we live with these forces our whole lives.  ( I should say our instincts feel the answer.)  The language of physics is just a way to talk about stuff we know already.

Not unlike observing bad behavior  ---We all know it when we see it but a term or explanation just just describes what we already know

It may seem to be a kind of trick question but it is not.

[Chargerguy74]

Acceleration is just the change in velocity per given time. It really has zero to do with the mass of an object, as it is only the rate of change of velocity. Acceleration due to gravity is a constant 9.81 m/s/s or 32.2 ft/s/s. No where in those units do you see lbs, kg, etc as mass has no influence on the acceleration by gravity. Why doesn't it? Why would it? The gravitational force of attraction between the mass of an object and the mass of the earth is like I said F=ma. So the force of attraction will be greater between the Earth and the car with greater mass, but the acceleration is still a constant (the earth's mass is constant) as it's only the rate of change of velocity. I know this still isn't a satisfying answer, and I don't think I can give you one.

[Chargerguy74]

I don't see it as a trick question. I've spent enough time with Applied Mechanics and Newton's laws of motion to see how these things work. "Why" is a totally different animal. Why is there a force of attraction between objects?

[ws23rt]

You are correct in your description of what is happening.

And the reason the acceleration rate is the same is?

[ws23rt]

Your question about ---why is there a force of attraction between objects?----

That is one that I have wondered about since I first fell down

It is IMHO the ---at the same time---- most predictable and least understood of the forces we live with.
Even magnetism is better understood.

[Chargerguy74]

You didn't really expect to get an answer here for why gravity works the way it does did you? I mean, is it even fully understood today among physicists? I was mistaken when I read the title of the thread "How stuff works" it's more of a "why things work the way they do". And for that, I do not have an answer 

[ws23rt]

You didn't really expect to get an answer here for why gravity works the way it does did you? I mean, is it even fully understood today among physicists? I was mistaken when I read the title of the thread "How stuff works" it's more of a "why things work the way they do". And for that, I do not have an answer.

No not at all.  That is not what I meant when I went on about how gravity is little understood.  It was a side comment about gravity.


Ok  here is a hint about the answer to the question---  The heaver car will not accelerate faster because it is heaver---