Physical Quantities

Many measures can be related to length $l$, time $t$, and mass $m$. Here are some common ones in astronomy:

speed is length per time, $l/t$

acceleration is speed per time, $l/t^2$

force is mass times acceleration, $ml/t^2$

energy is force times distance, $ml^2/t^2$

mass density is mass over volume, $m/l^3$

number density is number over volume, $1/l^3$

power (or luminosity) is energy per time, $ml^2/t^3$ (like wattage)

temperature is different, being given in degrees Celsius $C$ or Kelvin $K$

area is length squared, $l^2$

volume is length cubed, $l^3$

perimeter of a circle is circumference $c=2\pi r$

area of a circle of radius $r$ is $A = \pi\,r^2$

volume of a sphere of radius $r$ is $V= \frac{4\pi}{3}\,r^3$