Categories: Guide to Space

First Law of Thermodynamics

[/caption]

Ever wonder how heat really works? Well, not too long ago, scientists, looking to make their steam engines more efficient, sought to do just that. Their efforts to understand the interrelationship between energy conversion, heat and mechanical work (and subsequently the larger variables of temperature, volume and pressure) came to be known as thermodynamics, taken from the Greek word “thermo” (meaning “heat”) and “dynamis” (meaning force). Like most fields of scientific study, thermodynamics is governed by a series of laws that were realized thanks to ongoing observations and experiments. The first law of thermodynamics, arguably the most important, is an expression of the principle of conservation of energy.

Consistent with this principle, the first law expresses that energy can be transformed (i.e. changed from one form to another), but cannot be created or destroyed. It is usually formulated by stating that the change in the internal energy (ie. the total energy) contained within a system is equal to the amount of heat supplied to that system, minus the amount of work performed by the system on its surroundings. Work and heat are due to processes which add or subtract energy, while internal energy is a particular form of energy associated with the system – a property of the system, whereas work done and heat supplied are not. A significant result of this distinction is that a given internal energy change can be achieved by many combinations of heat and work.

This law was first expressed by Rudolf Clausius in 1850 when he said: “There is a state function E, called ‘energy’, whose differential equals the work exchanged with the surroundings during an adiabatic process.” However, it was Germain Hess (via Hess’s Law), and later by Julius Robert von Mayer who first formulated the law, however informally. It can be expressed through the simple equation E2 – E1 = Q – W, whereas E represents the change in internal energy, Q represents the heat transfer, and W, the work done. Another common expression of this law, found in science textbooks, is ?U=Q+W, where ? represents change and U, heat.

An important concept in thermodynamics is the “thermodynamic system”, a precisely defined region of the universe under study. Everything in the universe except the system is known as the surroundings, and is separated from the system by a boundary which may be notional or real, but which by convention delimits a finite volume. Exchanges of work, heat, or matter between the system and the surroundings take place across this boundary. Thermodynamics deals only with the large scale response of a system which we can observe and measure in experiments (such as steam engines, for which the study was first developed).

We have written many articles about the First Law of Thermodynamics for Universe Today. Here’s an article about entropy, and here’s an article about Hooke’s Law.

If you’d like more info on the First Law of Thermodynamics, check out NASA’s Glenn Research Center, and here’s a link to Hyperphysics.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:
http://en.wikipedia.org/wiki/First_law_of_thermodynamics
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/firlaw.html
http://en.wikipedia.org/wiki/Internal_energy
http://www.grc.nasa.gov/WWW/K-12/airplane/thermo1.html
http://en.wikipedia.org/wiki/Thermodynamics
http://en.wikipedia.org/wiki/Laws_of_thermodynamics

Matt Williams

Matt Williams is a space journalist and science communicator for Universe Today and Interesting Engineering. He's also a science fiction author, podcaster (Stories from Space), and Taekwon-Do instructor who lives on Vancouver Island with his wife and family.

Recent Posts

China Creates a High-Resolution Atlas of the Moon

Multiple space agencies are looking to send crewed missions to the Moon's southern polar region…

15 hours ago

Dinkinesh's Moonlet is Only 2-3 Million Years Old

Last November, NASA's Lucy mission conducted a flyby of the asteroid Dinkinish, one of the…

2 days ago

The Universe Could Be Filled With Ultralight Black Holes That Can't Die

Steven Hawking famously calculated that black holes should evaporate, converting into particles and energy over…

2 days ago

Starlink on Mars? NASA Is Paying SpaceX to Look Into the Idea

NASA has given the go-ahead for SpaceX to work out a plan to adapt its…

2 days ago

Did You Hear Webb Found Life on an Exoplanet? Not so Fast…

The JWST is astronomers' best tool for probing exoplanet atmospheres. Its capable instruments can dissect…

3 days ago

Vera Rubin’s Primary Mirror Gets its First Reflective Coating

First light for the Vera Rubin Observatory (VRO) is quickly approaching and the telescope is…

3 days ago