Sort of scientific question (not really).

Obfleur · Post by **Obfleur** » Tue Mar 27, 2007 1:36 pm

Lets say I am standing on a piece of rock that is hanging 500 meters above the ground.
The rock weighs 200 kg.
The rock starts falling - with me still standing on it.
I will probably die when the rock hits the ground.

But what happens if I jump straight up in the air when the rock is one meter above the ground?

Aaron Hong · Post by **Aaron Hong** » Tue Mar 27, 2007 1:52 pm

Most likely the rock would fall faster than you. You could cling to it and then jump at the last second but you'd need ninja timing to do that.

Personally I'd try jumping forward instead, tuck-and-roll, and hope it works out.

Obfleur · Post by **Obfleur** » Tue Mar 27, 2007 1:55 pm

[composite word including 'f*ck'] realism!
Lets say the rock and me fall at the same speed - and that I have ninja timing.

Brendocon · Post by **Brendocon** » Tue Mar 27, 2007 1:57 pm

Ultimately... not a lot. You jumping up would force the rock down with a bit more force and slow your descent a tad... most likely you'd just land on the rock and break yourself a fraction of a second later.

Unless, as Hong says, you jump forward. But in order to really pull that off you'd need to be a ninja or James Bond. Or Batman.

Obfleur · Post by **Obfleur** » Tue Mar 27, 2007 2:08 pm

So I can force the rock down even though it weighs more than me?
Would I be able to force down a two ton rock as well?

Aaron Hong · Post by **Aaron Hong** » Tue Mar 27, 2007 2:14 pm

Obfleur wrote:So I can force the rock down even though it weighs more than me?
Would I be able to force down a two ton rock as well?

Possibly, but at some point (the rock being somewhere between five tons and the size of a small moon) it'll become impossible.

Brendocon · Post by **Brendocon** » Tue Mar 27, 2007 2:14 pm

Well, if you're stood on top of it, the only way you can jump up is to exert pressure downwards (when you bend your knees and push up, you're creating a downward motion at the same time).

If the rock is descending through the air, then there's nothing below it to get in the way of that downward motion. The fact that it weighs shitloads doesn't come into it - you're pushing on something that's already moving in the direction you're sending it in. You may not make a noticeable difference, but the action will have at least some effect.

Most you can do is give gravity a pat on the back. Your jump will take you up a tiny bit (though you're already falling, so it may not be much), but gravity'll just turn round and say "where do you think you're going?" and pull you back down again. Seeing as the thing you're using to launch yourself upwards from is already moving in the direction you need to send it in order to lift yourself.

Physics to the rescue!

*waits for Rebis to arrive and contradict EVERYTHING I've said*

Obfleur · Post by **Obfleur** » Tue Mar 27, 2007 2:28 pm

Oooooh, okey.

Impactor returns 2.0 · Post by **Impactor returns 2.0** » Tue Mar 27, 2007 3:17 pm

Force = Mass x accelration.

And newtons 3 laws will solve this question.

there comes a point where the force u apply to the rock will move it.

This force will be equal to the mass of the object and its current accelration - which due to falling is 9.81 m/s squared but as u both falling at the same speed, it cancels out.

For example, if u are falling, u could throw a ball away from yourself but lets imagine your standing on a building sized object, falling through the air, u cannot push the object away because u cannot equal its mass, and thus u cannot create enough force.

So depdening on the weight of your rock, there is a point at which u can jump up from the rock, or u simply push the rock away.

If the both object were in total equal mass - then I belive u just displace the objects.

hmm, havent done projectiles since last year, ask me somthing based upon bending objects, heating them up, spinning them arround or other such enginering principles and im fine!

Guest · Post by **Guest** » Tue Mar 27, 2007 10:38 pm

The rock will fall at the same rate as you, as you are both experiencing the same gravitational attraction.

Conservation of Momentum shows us that the initial momentum of a system is equal to the final momentum of a system. Jumping from a falling rock will slow your descent, and speed up the rock's. As the rock is more massive, its descent is speeded up by less than yours is slowed.

Unfortunately, as you are jumping off at 1 metre to impact, you've got almost all the speed you'll get before impact, so jumping up at that point makes no difference, except you hit the ground a little later.

Out of interest, a fall of 500m generates an impact velocity of very nearly 100m/s, while a vertical jump equalling the high jump world record of 2.45m only generates an upwards velocity of 7m/s.

In any money that's basically a negligible change.

Oh, and for the record, no matter how massive the rock is, jumping off of it will alter its velocity, just by a lot less.

Even jumping up and down on the ground moves the Earth by an infinitessimal amount.

Obfleur · Post by **Obfleur** » Wed Mar 28, 2007 6:43 am

Interesting stuff!

Post by **Best First** » Wed Mar 28, 2007 7:36 am

yay Rebis.

Brendocon · Post by **Brendocon** » Wed Mar 28, 2007 7:44 am

Pfft. He just said what I said. He just used different words.

Eline · Post by **Eline** » Wed Mar 28, 2007 11:33 am

But how can you jump up from a non-steady surface?

Impactor returns 2.0 · Post by **Impactor returns 2.0** » Wed Mar 28, 2007 11:51 am

Like I was saying, I guess your mass would have to be less than the object you jump from.

Its like me jumping up from the earth, the earth moves a tiny bit in relation to the ratio of mass between me and the earth, which is, loads:1

Brendocon · Post by **Brendocon** » Wed Mar 28, 2007 12:11 pm

Eline wrote:But how can you jump up from a non-steady surface?

A trampoline is a non-steady surface.

Impactor returns 2.0 · Post by **Impactor returns 2.0** » Wed Mar 28, 2007 1:57 pm

but the elastic nature of the surface stores the energy you create.

Eline · Post by **Eline** » Wed Mar 28, 2007 3:14 pm

Brendocon wrote:
Eline wrote:But how can you jump up from a non-steady surface?
A trampoline is a non-steady surface.

trampolines make you happy

Guest · Post by **Guest** » Wed Mar 28, 2007 6:14 pm

Impactor returns 2.0 wrote:Like I was saying, I guess your mass would have to be less than the object you jump from.

Not necessarily. If the object has a much smaller mass, you'd just refer to your action as a kick instead.

Oh and to satisfy Brend, if you're falling with a rock, and you jump up from the rock, you'll still be moving down the whole time. You'll just appear to be moving up relative to the rock.

Brendocon · Post by **Brendocon** » Wed Mar 28, 2007 6:41 pm

Yes, you're just slowing your own descent.

Mechanics was the only bit of A-Level Maths I actually enjoyed.

Yaya · Post by **Yaya** » Wed Mar 28, 2007 6:42 pm

Rebis wrote: Unfortunately, as you are jumping off at 1 metre to impact, you've got almost all the speed you'll get before impact, so jumping up at that point makes no difference, except you hit the ground a little later.

Yeah, you'd get crushed regardless.

Post by **Best First** » Thu Mar 29, 2007 8:31 am

Phew! Jaja has confiremd that Rebis was correct. Praise be!

Post by **snarl** » Thu Mar 29, 2007 10:32 am

sorry, but this is all complete dog****.

If you jump off the rock 1 second before it lands, of course you will survive. Everybody knows this.

You sheep [composite word including 'f*ck'] dont know nothing about nothing, go watch some Wyle E Coyote cartoons you *****!

Guest · Post by **Guest** » Thu Mar 29, 2007 9:59 pm

Toontown physics is much better than flat earthers and their pre-Gallilean fallacies.

Impactor returns 2.0 · Post by **Impactor returns 2.0** » Thu Mar 29, 2007 10:12 pm

I just brought this up in physics.

Well funny chat.