Question about footprints!!

[Gregnat73]

Ok, so this question has nothing to do with astronomy but the other day a 6 year old at the school I work at asked me "why do wet feet leave footprints?" I said that the water on your shoe just sticks to the ground when you walk on it but then she said "why doesn't the water stay stuck to your shoe?" And I couldn't think of a good answer.... And ever since it's been driving me mad!! It seems like it should be simple (and I'm just being thick) but is there a proper scientific explanation?

[Mike Hawtin]

Well some of it does, but after each step less is left on the shoe until eventually there is none left.

[Paulhenry85]

Because the surface you are stepping on is absorbent.

[allcart]

Not Necessarily. you will still leave a wet footprint on a non absorbant surface. I'm sure it is just simply transferring water molecules with each step.

[Paulhenry85]

Not Necessarily. you will still leave a wet footprint on a non absorbant surface. I'm sure it is just simply transferring water molecules with each step.

Your question was "why doesn't the water stay stuck to your shoe?" The sciencitfic answer would be Cohesion, but I'm sure a six year would accept the surface being absorbant

[Paulhenry85]

Because the surface you are stepping on is absorbent.

Scientifically it's called Cohesive attraction or Cohesive force

[Knight of Clear Skies]

Ok, so this question has nothing to do with astronomy but the other day a 6 year old at the school I work at asked me "why do wet feet leave footprints?" I said that the water on your shoe just sticks to the ground when you walk on it but then she said "why doesn't the water stay stuck to your shoe?"

Children do ask some tricky questions! For a six-year old, I'd try the following explanation: water is sticky - it sticks to the ground and leaves footprints in exactly the same way that it sticks to your shoe in the first place.

[Gregnat73]

Thanks for the replies!! I did end up using the "water's sticky" explanation but she wasn't entirely convinced (kids eh?) I think we might need to do some investigations next week to prove it!!

Cheers

[Tiki]

This is a good "Why?" question.

...then she said "why doesn't the water stay stuck to your shoe?" And I couldn't think of a good answer.... And ever since it's been driving me mad!! It seems like it should be simple (and I'm just being thick) but is there a proper scientific explanation?

Answer: Some does. Not all of the water comes off on the first footprint.

Question: Why doesn't it all come off?

Partial answer: It is rather complicated and depends on a whole bunch of factors: gravity, shape and chemical composition of sole, shape and chemical composition of floor. It is the subtle interplay of these factors with surface tension and the pressures associated with footfall that account for the pattern of footprints.

Question: But why?

Answer: I don't know, i'm not sure if anyone really knows. Perhaps it is a question that science has not yet pursued.