Fluids

Fluids

What is it?

Fluids are substances whose molecules can flow past each other without causing cracks in the substance.

Give me an example!

When water is in a liquid state, it is a fluid. However, when it freezes and becomes a solid (or ice), it no longer flows. Fluids that flow very slowly (such as pancake syrup) are said to have a high viscosity.

Rotational and Irrotational Flow

Rotational and Irrotational Flow

What is it?

Rotational flow is when the particles of fluids are all rotating about their own axis in addition to their other movement. Irrotational flow is when the individual particles are not rotating around their axis.

Give me an example!

Water flows down a drain in a counterclockwise direction in the northern hemisphere, and in a clockwise direction in the southern hemisphere. That is because of the rotation of the individual water molecules combined with the acceleration due to gravity. By contrast, an example of irrotational flow would be the flow of water over a dam, in which the water flows straight down and rotation doesn't have an effect.

Continuum

Continuum

What is it?

A continuum is a line that traces the progress of something through space and time.

Give me an example!

Scientists often refer vaguely to the space/time continuum. This imaginary line traces the evolution of everything back to the beginning of time in one direction, and on until the end of time in the other direction. The "space" part of it means that all these things exist in space.