Here's why:
* Force is a vector: This means it has both magnitude (how strong it is) and direction.
* The negative sign: Indicates the direction of the force. In a one-dimensional system, a negative sign usually indicates the force is acting in the opposite direction to the positive direction.
Example:
If you define "up" as the positive direction, a -3 Newton force vector would represent a force of 3 Newtons pushing downwards.
It's important to remember: The choice of what direction is considered positive is arbitrary. You could define "down" as positive, in which case a -3 Newton force vector would represent a force of 3 Newtons pushing upwards.
