# The Naked Scientists Forum

### Author Topic: skydivers and their rate of fall.  (Read 6661 times)

#### paul.fr

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##### skydivers and their rate of fall.
« on: 23/11/2008 20:42:15 »
Two skydivers jump out of a plane, at the same time, and have forgotten their parachutes. One of them throws out the contents of his pockets, one by one. First the anvil, then the tennis ball and lastly his last £1 coin. In what order do they all hit the ground (men and objects)?

Edit:
both skydivers weigh the same...say 15 stone.
« Last Edit: 23/11/2008 20:43:46 by Paul. »

#### lyner

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##### skydivers and their rate of fall.
« Reply #1 on: 23/11/2008 23:13:17 »
Anvil first - least drag for a given weight.
Tennis ball last.
Man with full pockets before man with empty pockets
Throw me a lot of pound coins and I'll do the experiment. I'm not sure of the drag for a coin.

#### DoctorBeaver

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##### skydivers and their rate of fall.
« Reply #2 on: 23/11/2008 23:15:39 »

Throw me a lot of pound coins and I'll do the experiment. I'm not sure of the drag for a coin.

#### Bikerman

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##### skydivers and their rate of fall.
« Reply #3 on: 24/11/2008 01:55:36 »
Drag for a coin very great indeed - terminal velocity around 70kph.
Otherwise I agree with the previous analysis - anvil first and tennis ball last. Two skydivers will hit the ground around the same time (mass is not important - only drag).

PS - edit - dumb of me to say mass is not important  I meant to say ratio of mass/drag is important
« Last Edit: 24/11/2008 14:06:39 by Bikerman »

#### syhprum

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##### skydivers and their rate of fall.
« Reply #4 on: 24/11/2008 07:44:58 »
I disagree about both skydivers hitting the ground about the same time, the one whose pockets still contain an anvil although his drag will be increased by the bulge thereof will certainly get down first.

#### lyner

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##### skydivers and their rate of fall.
« Reply #5 on: 24/11/2008 09:19:49 »
terminal speed is set when drag equals weight

#### Bikerman

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##### skydivers and their rate of fall.
« Reply #6 on: 24/11/2008 13:54:28 »
Well, assuming no 'buoyancy' effect, we have:
Vt=√(2.m.g/(ρ.A.C))
Where Vt is terminal velocity, m = mass, g = gravity (9.81 ish), ρ = density of air, A is area of object, C is coefficient of drag

Obviously the important factors for our 2 skydivers will be mass and coefficient of drag (given all other factors should be roughly equal).
The question is, therefore, does the increased mass 'overpower' the loss of streamlining and subsequent increase in C? Simple answer is I don't know
« Last Edit: 24/11/2008 14:04:37 by Bikerman »

#### lyner

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##### skydivers and their rate of fall.
« Reply #7 on: 24/11/2008 15:14:28 »
I admit it's a matter of degree but 'anvil' implies a similar weight of steel to the weight of the jumper and a small increase in volume (anvils tend to be compact - see loony tunes!). In that case, the outcome is fairly predictable.

#### Bikerman

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##### skydivers and their rate of fall.
« Reply #8 on: 24/11/2008 15:17:21 »
I admit it's a matter of degree but 'anvil' implies a similar weight of steel to the weight of the jumper and a small increase in volume (anvils tend to be compact - see loony tunes!). In that case, the outcome is fairly predictable.
Agreed, but the possibility of someone walking around with an anvil in their pocket struck me as rather remote and I therefore assumed we might be talking about something rather less massive

#### lyner

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##### skydivers and their rate of fall.
« Reply #9 on: 24/11/2008 17:55:38 »
I suppose I would be wrong to refer you to the original post.
Sorry :-)
(Big pockets)

#### Bikerman

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##### skydivers and their rate of fall.
« Reply #10 on: 24/11/2008 18:01:16 »
Well, the OP might have meant a really tiny anvil used to shoe ants

#### lyner

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##### skydivers and their rate of fall.
« Reply #11 on: 25/11/2008 17:16:05 »
Or an anvil of change? (Say it)

#### Bored chemist

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##### skydivers and their rate of fall.
« Reply #12 on: 25/11/2008 20:32:15 »
Or an anvil of change? (Say it)

****!

#### lyner

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##### skydivers and their rate of fall.
« Reply #13 on: 25/11/2008 22:25:29 »
It's the way I tell em.

#### paul.fr

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##### skydivers and their rate of fall.
« Reply #14 on: 27/11/2008 23:15:21 »
(anvils tend to be compact - see loony tunes!)

You noticed the "clever" way i substituted Wile E. Coyote for two skydivers.

Agreed, but the possibility of someone walking around with an anvil in their pocket struck me as rather remote and I therefore assumed we might be talking about something rather less massive
Never imagine there to be any thought behind the question.

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##### skydivers and their rate of fall.
« Reply #15 on: 27/11/2008 23:30:52 »
The sky divers are obviously time lords as they have TARDIS pockets.

I disagree about both skydivers hitting the ground about the same time, the one whose pockets still contain an anvil although his drag will be increased by the bulge thereof will certainly get down first.

I think the bulge might be to do with fear! Is that an anvil in your pocket or are you just pleased to see me?

I think if the anvil sticks out enough then this WILL slow the man down. If he is a time lord and the anvil doesn't spoil the crease of his trousers then he will hit the floor at the same time as the other guy, unless of course, someone puts an acme roll out hole under said man.

#### The Naked Scientists Forum

##### skydivers and their rate of fall.
« Reply #15 on: 27/11/2008 23:30:52 »