What are 3 different forces that act on objects on the earth ωvω

A force is a push or pull acting upon an object as a result of its interaction with another object. There are a variety of types of forces. a variety of force types were placed into two broad category headings on the basis of whether the force resulted from the contact or non-contact of the two interacting objects.

Contact Forces

Action-at-a-Distance Forces

Frictional Force
Gravitational Force
Tensional Force
Electrical Force
Normal Force
Magnetic Force
Air Resistance Force
Applied Force
Spring Force

These are types of individual forces

Applied Force
Gravitational Force
Normal Force
Frictional Force
Air Resistance Force
Tensional Force
Spring Force

The independent variable would be the fertilizer as it is what the dependent variable (the growth of grass) depends on.