Featured Research

from universities, journals, and other organizations

Droplets That Roll Uphill

Date:
September 26, 2007
Source:
American Physical Society
Summary:
Physicist have shown that liquid drops can defy gravity. Droplets of liquid on an inclined plate that is shaken up and down can travel uphill rather than sliding down. In fact, if the plate vibrates at the right rate, the droplets will always travel counter-intuitively up the incline.

Droplets of a glycerol-water mixture defy gravity to climb up hill, provided the surface under them is shaken in the right way. The discovery may lead to new methods to manipulate microscopic amounts of fluids.
Credit: P. Brunet, J. Eggers, and R.D. Deegan

We are all familiar with raindrops on our wind screens. The small ones stay in place while the big ones roll down the window. This is because surface tension holds the small drops onto the screen until they get to a size where the force of gravity is greater than the surface tension.

But mathematicians at the University of Bristol have shown that the small drops can defy gravity and travel up hill – even on an incline as steep as 85 degrees – if the surface vibrates up and down sufficiently strongly.

A recent experiment conducted by physicists at University of Bristol in the United Kingdom has shown that liquid drops can indeed defy gravity. Droplets of liquid on an inclined plate that is shaken up and down can travel uphill rather than sliding down. In fact, if the plate vibrates at the right rate, the droplets will always travel counter-intuitively up the incline.

The reason has to do with pushing and pulling. As the plate rises, it pushes the droplet upward, and as it falls, it pulls the droplet down. Inertia would have the droplet slide down as the plate moved upward. Similarly, the droplet would climb up the incline as the plate drops, resisting the rapid downward acceleration.

However, the forces that hold the droplet to the plate are stronger as the plate rises. During the time that the droplet would be moving downhill, it is stuck more firmly to the plate. Therefore, the droplet gains more ground moving up the incline as the plate falls than it loses as the plate rises. Overall, the droplets travel uphill.

If the vibration doesn't apply enough force to the droplet, it will just sit still on the inclined plate. As the force increases, the droplet will begin to slide. Increasing the forces further, the droplet sits still again. Turn up the force on the droplet a little more, and it starts to climb.

Since the droplet must withstand a fair amount of force, alternately pushing and pulling, the fluid has to be somewhat thick or viscous. Pure water droplets will break apart before the forces are strong enough to cause them to climb. On the other end, the drops move very slowly if the fluid is too thick. Nevertheless, this method for moving droplets using vibrations may prove useful in the manipulation of microscopic fluids.

Dr Philippe Brunet of the University of Bristol said, “Moving small droplets – such as thousands of spots of DNA arranged on a solid surface (a DNA microarray) – is very difficult as their small size causes them to stick to the surface. So improving our understanding of what causes droplets to move on surfaces will help with this and similar problems.”

The authors of the research to be published in a forthcoming issue of Physical Review Letters are P. Brunet, J. Eggers, and R.D. Deegan.


Story Source:

The above story is based on materials provided by American Physical Society. Note: Materials may be edited for content and length.


Cite This Page:

American Physical Society. "Droplets That Roll Uphill." ScienceDaily. ScienceDaily, 26 September 2007. <www.sciencedaily.com/releases/2007/09/070924143342.htm>.
American Physical Society. (2007, September 26). Droplets That Roll Uphill. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2007/09/070924143342.htm
American Physical Society. "Droplets That Roll Uphill." ScienceDaily. www.sciencedaily.com/releases/2007/09/070924143342.htm (accessed July 28, 2014).

Share This




More Matter & Energy News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins