Cells and atoms.
Volume and mass.
Size and shape.
Weight and gravity.
Are vague and non-scientific.
Are measurable and reproducible.
All of these
Conversion of solid directly into gas
Conversion of gas into liquid
Conversion of gas directly into solid
Conversion of liquid into solid
Temperature against mass
Temperature against kinetic energy
Available space against kinetic energy
Temperature against time
The force that causes a fluid to stick to something.
The thickness of a fluid.
The speed of a fluid.
A measure of the speed of a fluid.
The thickness of a fluid
The weight of a fluid.
Here's an interesting quiz for you.