Forces as Vectors

A force is an interaction between two objects that can cause a change in motion. Forces have both strength and direction, making them vector quantities.

Forces arise in two ways. Contact forces require objects to touch, like pushing a book or friction between surfaces. Long-range forces act over a distance without contact, such as gravity, magnetism, or electric forces.

In the SI system, force is measured in newtons (symbol: $\text{N}$). One newton is the force needed to accelerate a one-kilogram mass at one meter per second squared: $1~\text{N} = 1~\text{kg}\cdot\text{m/s}^2$. We will discuss this in more detail in future lessons on Newton's Laws.

Since forces are vectors, we represent them with arrows. The arrow's length shows the magnitude or strength of the force, and its orientation shows the direction the force is applied in.