Which statement correctly distinguishes contact and non-contact forces?

Which statement correctly distinguishes contact and non-contact forces?

• A. Contact forces require physical contact; non-contact forces act at a distance.
• B. Non-contact forces act at a distance; contact forces require physical contact.
• C. There is no difference between them.
• D. Both contact and non-contact forces always require motion in the same direction.

Answer: (A)

The main idea is whether interaction between objects requires them to touch. Contact forces come from direct physical contact—friction between surfaces, the normal force from a surface, and the force transmitted through a rope or pushing on an object. Non-contact forces act without touching, via fields that reach across space—gravity pulling on you from Earth, or magnetic and electrostatic forces between objects that aren’t in contact. So the statement that contact forces require physical contact and non-contact forces act at a distance captures this essential distinction. For contrast, the other options mix up the roles (non-contact forces don’t always have to act at a distance, and contact forces don’t always involve motion in the same direction), which isn’t how these forces are defined.

The main idea is whether interaction between objects requires them to touch. Contact forces come from direct physical contact—friction between surfaces, the normal force from a surface, and the force transmitted through a rope or pushing on an object. Non-contact forces act without touching, via fields that reach across space—gravity pulling on you from Earth, or magnetic and electrostatic forces between objects that aren’t in contact.

So the statement that contact forces require physical contact and non-contact forces act at a distance captures this essential distinction. For contrast, the other options mix up the roles (non-contact forces don’t always have to act at a distance, and contact forces don’t always involve motion in the same direction), which isn’t how these forces are defined.