Maths bods - a question please

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GordonG Jul 2016 12:55pm, 5 Jul 2016 6,894 posts	0 GordonG Hi all Youngest GordonG and I were discussing his journey to school the other day, in the pouring rain. He wanted to cycle to school but I thought that he would get more wet on a bike than walking. I’ve been thinking about it since, but my Grade E GCE maths brain can’t quite cope. I’ve kinda got some of it figured out but would appreciate your thoughts. My bottom line question is: would my son get wetter walking or cycling to school? My bonus question is that if someone is clever enough to come up with a formula for this, that would be great. So here’s the scenario: Youngest GordonG can cycle to school in 5 mins. He can walk it in 20. If it’s raining (and let’s assume that the rain is falling at a constant rate throughout) it seems obvious that if he’s out in the rain 4 times longer walking than cycling then he’ll get 4 times wetter walking. And the basic formula for how much water would fall on him would be something like: Minutes spent in rain x the amount of rain that falls per minute – is this correct? But – and here’s the bit I’m struggling with – he’ll also be going faster on a bike. In my mind, if two people are standing still but the rain is falling four times heavier on one person than the other, the person under the heavy rain will get wetter. So as he’s going four times faster on a bike than when walking (5 mins to cycle vs 20 mins to walk) is this like getting hit by rain four times heavier? But as he is going to be out in the rain for only one quarter of the time do the two things cancel each other out and maybe he’ll get equally wet regardless of the mode of transport? Any thoughts? ta PS getting a bus isn't an option!
Duchess Jul 2016 1:00pm, 5 Jul 2016 6,965 posts	0 Duchess Why would the rain be falling heavier on him whilst cycling than walking?
GregP Jul 2016 1:02pm, 5 Jul 2016 83,132 posts	0 GregP This sounds like one for the Excel wire ('SpreadEveryone'). We love a bit of applied maths over there. Okay if I cut and paste?
fetcheveryone Jul 2016 1:03pm, 5 Jul 2016 17,365 posts	0 fetcheveryone As far as my understanding goes, it's all about surface area and time. If you assume that the rain is falling in a uniform way, then each square metre of ground will receive the same amount each second. Likewise, the top of your sons head will receive the same amount per second, irrespective of where it happens to be. However, if he's leaning forward when pedalling, he's increasing his area to include his back and possibly his legs, so he will get more rain because of that.
ChrisThePuma Jul 2016 1:03pm, 5 Jul 2016 3,412 posts	0 ChrisThePuma Does this help: physlink.com
fetcheveryone Jul 2016 1:04pm, 5 Jul 2016 17,366 posts	0 fetcheveryone He needs a cycle helmet with a good guttering system.
sinj999 Jul 2016 1:04pm, 5 Jul 2016 394 posts	0 sinj999 What angle is the rain coming down at? If straight down then he would only get wet on top of head and shoulders when walking. When cycling he would get more frontal coverage due to travelling at a faster speed into the rain presenting a greater surface area.
GregP Jul 2016 1:07pm, 5 Jul 2016 83,134 posts	0 GregP I've seen this before on a triathlon forum somewhere (not the Hotel - so probably Slowtwitch - it's beyond the intellectual capacity of the Tri Talk lot ;)). I think Fetch is right, but I've got a sneaking suspicion that the thing I read 'proved' otherwise. ~wanders of to reat CtheP's link~
JJ Flash Jul 2016 1:07pm, 5 Jul 2016 5,241 posts	0 JJ Flash FFS, just buy the boy a coat!
Rosehip Jul 2016 1:07pm, 5 Jul 2016 7,538 posts	0 Rosehip walking vs running was done on both mythbusters discovery.com (and brainiac - but I can't find that link) cba to watch and see what the outcome was and no idea if it applies to cycling my thought is he'd get more splashed by cars on bike than walking