How Does Bathwater Give Off Steam? - Scientific American

July 28, 2009

1 min read

Add Us On GoogleAdd SciAm

How does bathwater give off steam?

Herman Merte, a professor emeritus of mechanical engineering at the University of Michigan at Ann Arbor, explains

By Herman Merte

Join Our Community of Science Lovers!

Sign Up for Our Free Daily NewsletterEnter your emailI agree my information will be processed in accordance with the Scientific American and Springer Nature Limited Privacy Policy. We leverage third party services to both verify and deliver email. By providing your email address, you also consent to having the email address shared with third parties for those purposes.Sign Up

Herman Merte, a professor emeritus of mechanical engineering at the University of Michigan at Ann Arbor, explains:

What one sees drifting above a hot bath—often called “steam”—is in fact tiny drops of liquid water that have coalesced out of the gaseous mixture of air and water vapor above the fluid’s surface. The vapor, itself an invisible gas, arises from evaporation, whereby water molecules escape from a liquid. Evaporation is a slower process than boiling but is accelerated when water heats up (gaining increased energy).

The conditions under which invisible water vapor condenses into visible mist depend on the ambient temperature and the amount of water vapor in the air. Compared with cold air, warm air can hold more water vapor before becoming so saturated that condensation occurs. This property explains why a bath—or a cup of tea—emits more visible steam on a cold winter morning than on a hot summer afternoon.

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Note: This article was originally printed with the title, "How does bathwater well below the boiling point give off steam?"

It’s Time to Stand Up for Science

If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.

I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.

If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.

In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.

There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.

Thank you,

David M. Ewalt, Editor in Chief, Scientific American

Subscribe

Subscribe to Scientific American to learn and share the most exciting discoveries, innovations and ideas shaping our world today.

Subscription PlansGive a Gift Subscription