Question

Question #6e113

Answer 1

Sometimes, the basic equations just have to be memorized and used before they become familiar.

Explanation:

If you understand the concepts you can use that to work out many of the equations. For example, density is the ratio of mass to volume. So, you need a mass and volume term to calculate it. Or, you can use it and one of the others to calculate the third term.

Similarly, energy is usually a combination of components, like frequency and wavelength. `E = h xx nu`

That is identical in form to the Distance equation:
`"Distance" = "Rate" xx "Time"`

So, if you think of energy as the distance (the result), then 'wavelength' may correspond to the 'rate' (how long is the unit) and 'frequency' to the time - how fast it moves.

Other conversions between units can be done best with "Dimensional Analysis", which means that you set up the terms to properly define the final units before you put any numbers into an equation. Then at least you know what other terms or factors you need to derive the desired answer.

For example, if I want `"kg"/m^3` and I am given pounds and cubic feet `"lbs"/"ft"^3`, I need to have conversions of kilograms to pounds and cubic meters to cubic feet in order to derive the correct final value.
`cancel"lbs"/cancel"ft"^3 xx "kg"/cancel"lbs" xx cancel"ft"^3/m^3 = "kg"/m^3`