Read more about solids, liquids and gases in our study guide about states of matter. In a system, the energy of the particles, which can be atoms or molecules, is known as the internal energy.

The rest of the universe appears to be made of a mysterious, invisible substance called dark matter (25 percent) and a force that repels gravity known as dark energy (70 percent). Scientists have ...

Read more about the states of matter in our study guide about temperature changes and energy. In a system, the energy of the particles, which can be atoms or molecules, is known as the internal ...

Dark energy and dark matter refers to the unseen energy and matter components of the Universe. Dark matter is invisible, non-baryonic matter hypothesized to explain phenomena including ...