Resultant force

• Often several forces act on one body.
• Their vector sum is the resultant (net) force, written ΣF (read "sigma F").
• Forces in the same line are added with signs (+ in one direction, − in the opposite one).

Example 1. A box on the floor is pulled to the right by 30 N and to the left by 10 N (friction). ΣF = 30 − 10 = 20 N to the right.

Example 2. The same box is pulled by 30 N to the right and 30 N to the left. ΣF = 0: the forces are balanced and the box keeps its state of motion.