Ais a standard amount like a kilometer or gallon when used to communicate different quantities

I think the missing word you're looking for here is 'unit'. The examples such as kilogram and gallons are all units of measurement. These are standard amounts used for mass, volume, and length. It is especially important to be consistent with this units especially when doing dimensional analysis.

Answer;

hot magma rises and pushes up toward the lithosphere, and as it cools it cycles back down toward the core to be heated again.

explanation; convection currents are the circular pathways taken by a fluid that enhances heat transfer by the process known as convection which occurs in fluids.convection currents transfer heat from one place to another by mass motion of a fluid. earth mantle is in a semi-liquid state and behaves like any other fluid, rising up from the bottom of the mantle after becoming hotter and less dense from heat of the earth's core, as the rock loses heat into the earth's crust it becomes cooler and more dense, then sinking back down to the core, then repeating the cycle.

Projectile motion is a form of motion experienced by an object or projectile that is thrown near the earth's surface and moves along a curve path under the action of gravity.