Forces are described by their strength and direction. The strength of a force is measured in units of newtons (N).

Force diagrams use arrows to represent forces, with arrow length indicating relative strength. Force diagrams should also include a speed arrow to show in which direction it is moving.

When two objects interact, they exert equal and opposite forces on each other.

The effect on an object's motion is the result of combined forces, not just the strongest.

Balanced forces result in no motion change; unbalanced forces lead to changes in speed and direction.

A non-zero net force on a stationary object initiates motion.

Net force in the direction of motion increases speed; opposite direction decreases speed.

Friction, an opposing force, can eventually stop and reverse motion.

A balanced combination of forces maintains an object's state: at rest or in constant motion.

Net force strength correlates with the rate of change in speed.

Mass influences the rate inversely (inertia).

A force from the side changes an object's path.

Moving through the air subjects an object to air resistance or drag.

Drag strength depends on object speed and surface area.