How do non contact forces differ from contact forces?

To differentiate between non-contact forces and contact forces, let's evaluate the statements you've presented:

(A) Non-contact forces are always present - This statement is not entirely accurate. While non-contact forces (like gravity and electromagnetic forces) can act at a distance, they are not "always present" in the sense that they don't always exert force on an object unless certain conditions are met.

(B) Non-contact forces can only be attractive - This statement is also incorrect. While gravity is an attractive force, electromagnetic forces can be both attractive and repulsive, depending on the charges involved.

(C) Contact forces behave differently in space - This statement is misleading. Contact forces (like friction, tension, and normal force) require physical interaction between objects, which do not exist in the vacuum of space. Thus, there is no "contact force" in the traditional sense in space where no physical touch occurs.

(D) Contact forces can be exerted through objects - This statement is accurate, as contact forces like tension and normal force occur due to direct physical interaction between objects.

Given the context and accuracy of the statements, (D) is the best answer that reflects a key difference between contact forces and non-contact forces.