Explain the effect of earts gravity on objects on the
surface of earth

There's a pair (2) of equal and opposite forces of gravity between every two objects.  The strength of the forces depends on the mass of the objects.

The Earth's mass is so huge that, when an object is on or near the Earth's surface, we actually notice the force of gravity pulling the object toward the center of the Earth. We call that force the "weight" of the object.

Nobody ever talks about the force of gravity pulling the Earth toward the object, but it's equal.

Your weight on the Earth is EQUAL to the Earth's weight on YOU !

the area between the graph and the t axis