Definitions


Density - In science terms, it is the ratio of mass to volume. In normal people terms, it's how much stuff is stuffed into a given space. For example, a rock is more dense than a feather. In other words, if a rock and feather are the same size, the rock weighs more and is therefore, more dense.


Gravity - In science terms, it is the downward force exerted on an object. In normal people terms, it's what keeps people "grounded" (Naughty force) It also keeps the planets where they are in space. It would be bad to collide with Jupiter.


Troposphere - From the Greek, "tropo" meaning mixing and "sphere" meaning globe. In English, the layer in our atmosphere that is home to weather.


Cross Section - A vertical slice of the atmosphere.  If we take a cross section of an orange, it looks like a CD with out the hole, with pieces, and great flavor.


Gradient - The rate of change of a given quantity.  For example, if the pressure changes rapidly over a short distance, then there will be a strong "gradient" of pressure.