Why Does Water Move on a Hot Surface Instead of Evaporating Immediately?

  • Context: High School 
  • Thread starter Thread starter The_Z_Factor
  • Start date Start date
  • Tags Tags
    Heat Water
Click For Summary

Discussion Overview

The discussion revolves around the behavior of water droplets on a hot surface, specifically why they move around instead of evaporating immediately. This includes exploration of physical phenomena such as surface tension and the Leidenfrost effect, with a focus on the interaction between heat and water at the molecular level.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • The initial observation describes a water droplet moving on a hot stove without immediate evaporation.
  • Some participants suggest that surface tension keeps the droplet intact while it is boiling.
  • One explanation posits that the droplet rides on a cushion of steam, which forms upon contact with the hot surface, preventing direct contact and allowing it to remain for several seconds.
  • There is a question raised about the duration of the droplet's behavior, specifically whether it can last for 15 to 20 seconds.
  • Another participant confirms the possibility of the droplet surviving for that duration due to low thermal conductivity of steam or air, and notes the droplet's jumping motion as steam expands.
  • A reference to the Leidenfrost effect is made, which is relevant to the observed behavior of the droplet.

Areas of Agreement / Disagreement

Participants generally agree on the mechanisms at play, such as the role of steam and surface tension, but there is some uncertainty regarding the specific duration and conditions under which the droplet behaves as described. The discussion does not reach a definitive consensus on all aspects.

Contextual Notes

Some assumptions about the conditions of the experiment, such as the exact temperature of the stove and the properties of the water droplet, remain unspecified. The discussion also does not resolve the nuances of the Leidenfrost effect in this context.

The_Z_Factor
Messages
70
Reaction score
0
I was boiling some water the other day in a pot and the stove was already hot, and a drop of water dripped from the pot onto the stove and it didnt evaporate or anything it just moved around all over the place until eventually about maybe 15-20 seconds later it "rolled" off the hot part of the stove and just evaporated or disappeared I am not exactly sure what happened.

So why does this happen? I mean, why does the water move the way it does over a hot surface, does something happen to those atoms in it so that when it comes in contact with heat they all just go crazy?
 
Science news on Phys.org
Surface tension holds it in a single dropplet while it is boiling away. And the heat and boiling makes it move around as it is boiling.
 
If I understand the OP's scenario correctly, then what's happening is that the droplet is riding on a cushion of steam that forms as soon as the drop touches the overheated surface. The tiny layer of steam prevents direct contact between the droplet and the stove, keeping the droplet "alive" for several seconds. Sooner or later, the droplet loses balance (or the steam dissipates) and falls off the steam cushion, hits the surface, and boils away.
 
Last edited:
could this really happen for 15 to 20 seconds
 
Apparently so.
 
I've witnessed this a few times, but never thought to ask why it happened. Thanks for the input.
 
I think the explanation of Gokul is correct. Steam or air has very low thermal conductivity so the droplet can survive quite a time. You can also see it jumping, because steam is created and expands suddenly making the droplet hover off the oven surface
 
By the way, it's known as the http://en.wikipedia.org/wiki/Leidenfrost_effect" effect.
 
Last edited by a moderator:
Ahh thank you everybody, and thanks cesiumfrog for the link, that pretty much sums it up.
 

Similar threads

  • · Replies 66 ·
3
Replies
66
Views
5K
  • · Replies 32 ·
2
Replies
32
Views
4K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 16 ·
Replies
16
Views
7K
  • · Replies 9 ·
Replies
9
Views
15K
  • · Replies 20 ·
Replies
20
Views
35K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K