The diagram above is a soil profile. it represents different soil layers and the parent material from which the soil forms. the topsoil layer is at or near the surface, and the parent material can be several meters below the surface.

porosity is one of many characteristics that varies in soil. porosity is a measure of how much empty space a soil sample has between its particles—the more empty space there is, the greater the porosity.

given that particles deeper underground tend to pack more closely together due to gravity, place the soil layers in order of increasing porosity.

a. c horizon → subsoil → topsoil

b. topsoil → c horizon → subsoil

c. topsoil → subsoil → c horizon

Learning goal: to understand newton's 1st law. newton's principia states this first law of motion: an object subject to no net force maintains its state of motion, either at rest or at constant speed in a right line. this law may be restated as follows: if the sum of all forces acting on an object is zero, then the acceleration of that object is zero. mathematically this is just a special case of the 2nd law of motion, f⃗ =ma⃗ , when f⃗ =0. when studying newtonian mechanics, it is best to remember the 1st law in two ways: if the net force (i. e., sum of all forces) acting on an object is zero, the object will keep moving with constant velocity (which may be zero). if an object is moving with constant velocity, that is, with zero acceleration, then the net force acting on that object must be zero. complete the following sentences to see if you can apply these ideas. part a if a car is moving to the left with constant velocity, one can conclude that