Lever & location This is regarding all types but is mainly geared towards Class 1 and Class 2 levers.

With the Class 1 lever picture above for example.
What factors would cause the entire lever system (crowbar, fulcrum, and the rock), when the crowbar is halfway pressed down and the rock is off the ground, to move backwards or forwards from there original starting location?
In other words, say the crowbar, fulcrum, and the rock were all one solid piece. The crowbar is pressed down resulting in the rock lifting up. Now, when the rock is lowered to the ground, the rock is about $5\; in$ (I'm just putting in a number here) away (forwards or backwards, you pick the direction), from where the rock was before it was picked up. Since the whole thing is one piece the entire piece has moved 5 inches. In this example, there are absolutely no pushing forward or pulling backwards forces on the entire piece.
(For a visual idea of what I am referring to picture kids on a seesaw. Every time the kids go up and down; the entire seesaw moves forwards or backwards a little.)
I would like to know what factors would cause the whole lever system to move while the lever is being used?
 A: Consider the class 1 lever in the figure, such that the crowbar and fulcrum are affixed at a pivot (by, say, a pin) to each other. There are four external forces acting on the mechanism, namely,

*

*the effort force applied to the left end crowbar directed vertically downwards,

*the reaction force acted by the load on the right end of the crowbar (equal and opposite to the action force acted by the right end of the crowbar on the load),

*the reaction force directed vertically upwards, by the ground on the mechanism and

*the friction force directed horizontally, by the ground on the mechanism.

The direction in which the crowbar applies the contact force on the load (rock in this case) is not vertical, so that neither is the angle at which the reaction force (to the action force) (#2) is applied by the load on the crowbar. At the same time, the effort force (#1) applied to the mechanism and the reaction force ($3) by the ground on the mechanism are typically directed close to vertical. Therefore, the crowbar-fulcrum mechanism is subjected to a net external horizontal force which is directed leftwards in the specific example illustrated in the figure. This force can cause the mechanism to move leftwards if the static friction force (#4) acting on it is significantly lower than the horizontal reaction force acted by the load on it.
In short, the difference between the horizontal force component of the force # 2 and force # 4, which is non-vanishing and directed leftwards in general in this example, are the forces which cause the crowbar-fulcrum lever mechanism to move leftwards.
A similar qualitative analysis can be easily presented for the class 2 levers.
