Liquids in the Universe Liquids on Earth What makes a liquid? Viscosity

Liquids are probably the second most familiar state of matter to most people. We use oil in our cars and kitchens. We drink water, wash with it, swim in it and sail on it. Our own bodies are primarily composed of liquid - we are 80% water!

Liquids in the Universe
Liquid is probably the rarest state in the Universe, with the only discovered, naturally occurring liquids being the Earth's surface water and our liquid metal core. Some astronomists believe that there may be water on a few of the moons in the outer Solar System and that water may have once existed on Mars due to its extensive canyons.

Liquids on Earth
Although most of the outer part of our planet is solid, this solid mantle sits on a liquid outer core and is two thirds covered in liquid water. By mass, liquids are the most common state on and in the Earth.

What makes a liquid?
Typically, liquids occupy a set volume and have the ability to change shape. Liquids change shape to occupy the bottom of their container until their volume is achieved. If they are not held in a container, they will flow under the influence of gravity. Small amounts of liquid will form drops, held together by attractive forces between the particles.

Substances which are liquids under normal conditions (25°C and 1 atmosphere pressure) are usually made of medium to heavy atoms or molecules, which are tightly bonded together. The particles in a liquid may vibrate and spin with kinetic energy like a solid, but they will also have enough motion to move about, always staying in contact with other particles in the liquid.

Particles in a liquid.

Viscosity
The most obvious physical feature that can be observed in liquids is how "runny" they are (viscosity). For example, honey and treacle flow very slowly, while petrol and mercury flow easily. Honey and treacle are described as having high viscosity, while petrol and mercury have low viscosity.

Viscosity.

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