Here's why:
* Work is defined as the force applied to an object multiplied by the distance the object moves in the direction of the force.
* Contact forces are forces that occur when two objects are in direct contact with each other. Examples include:
* Friction: The force that opposes motion between two surfaces in contact.
* Normal force: The force exerted by a surface on an object in contact with it.
* Tension: The force transmitted through a rope, string, or cable when it is pulled taut.
* Applied force: A force directly applied to an object by a person or another object.
Non-contact forces (like gravity or magnetism) can also affect the motion of an object, but they don't do work unless the object actually moves in the direction of the force.
Think of it this way:
* You can push a box across the floor (applying a contact force) and do work because the box moves in the direction you pushed.
* Gravity pulls on a book on a table, but the book doesn't move unless you pick it up (doing work by applying a contact force).
Let me know if you'd like more details on any of these forces!
