The physical bodies (a living being, the Sun, the atmospheric air...) can be classified according to whether the body can exchange matter and/or energy or not:
| Exchange E | Exchange M | Examples | |
|---|---|---|---|
| Open systems | Yes | Yes | Any living being: a plant, for example, takes in solar energy, takes in matter (nutrients from the soil and the air), releases energy (heat) and releases matter (O2, seeds, leaves, etc.). |
| Closed systems | Yes | No | The Earth is said to be very much like a closed system, as it exchanges energy (receiving solar radiation and giving off heat) but almost no matter; but think for example of a meteoroid falling down to the Earh or an astronaut losing a screwdriver in outer space... these are exchanges of matter. |
| Isolated systems | No | No | They just don't exist in Nature: it is difficult to think of any object that never receives any kind of radiation from any star some light years away. |



Topic 1
Last updated: 06 May 2008
Printed: 13 May 2008
