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 September 17, 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 September 17, 2014).

Share This



More Matter & Energy News

Wednesday, September 17, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Space Race Pits Bezos Vs Musk

Space Race Pits Bezos Vs Musk

Reuters - Business Video Online (Sep. 16, 2014) Amazon CEO Jeff Bezos' startup will team up with Boeing and Lockheed to develop rocket engines as Elon Musk races to have his rockets certified. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
MIT's Robot Cheetah Unleashed — Can Now Run, Jump Freely

MIT's Robot Cheetah Unleashed — Can Now Run, Jump Freely

Newsy (Sep. 16, 2014) MIT developed a robot modeled after a cheetah. It can run up to speeds of 10 mph, though researchers estimate it will eventually reach 30 mph. Video provided by Newsy
Powered by NewsLook.com
Manufacturer Prints 3-D Car In Record Time

Manufacturer Prints 3-D Car In Record Time

Newsy (Sep. 15, 2014) Automobile manufacturer Local Motors created a drivable electric car using a 3-D printer. Printing the body only took 44 hours. Video provided by Newsy
Powered by NewsLook.com
Refurbished New York Subway Tunnel Unveiled After Sandy Damage

Refurbished New York Subway Tunnel Unveiled After Sandy Damage

Reuters - US Online Video (Sep. 15, 2014) New York officials unveil subway tunnels that were refurbished after Superstorm Sandy. Nathan Frandino reports. Video provided by Reuters
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