Know how long you can store certain foods in the fridge/freezer. It happens to many of us: storing foods in our freezer for who knows how long and then taking it out only to find its rotten or disgusting.

This handy guide from the U.S. Food and Drug Administration for Food Safety charts the length of time food should be kept in the refrigerator or freezer. These short but safe time limits will help keep refrigerated and frozen food from spoiling or becoming dangerous. After looking at the chart, I will definitely throw out some of my food.

Energy density is the amount of energy stored in a given system or region of space per unit volume, or per unit mass, depending on the context. In some cases it is obvious from context which quantity is most useful: for example, in rocketry, energy per unit mass is the most important parameter, but when studying pressurized gas or magnetohydrodynamics the energy per unit volume is more appropriate. In a few applications (comparing, for example, the effectiveness of hydrogen fuel to gasoline) both figures are appropriate and should be called out explicitly. (Hydrogen has a higher energy density per unit mass than does gasoline, but a much lower energy density per unit volume in most applications.)Energy density per unit volume has the same physical units as pressure, and in many circumstances is an exact synonym: for example, the energy density of the magnetic field may be expressed as (and behaves as) a physical pressure, and the energy required to compress a gas may be determined by multiplying the pressure of the compressed gas times its change in volume.