VCE Physics

## Force as a vector A force is a push or a pull on an object, measured in newtons (N), and it has both size and direction, so it is a vector. Forces are drawn as arrows on a free-body diagram, which shows one object alone with every force acting on it and nothing else. Each arrow starts on the object and points the way the force acts. A force is always exerted by something, so if you cannot name what is exerting an arrow, it should not be there. In particular, there is no "force of motion" in the direction an object is travelling: velocity needs no force to keep going, only to change. The forces met most often are listed below. | Force | Symbol | Direction | Comment | |---|---|---|---| | Weight (gravity) | $F_g$ or $mg$ | Towards the centre of Earth | Near the surface $F_g = mg$, with $g = 9.8\,\mathrm{m\,s^{-2}}$ | | Normal force | $N$ | Perpendicular to the surface, away from it | Adjusts to whatever value stops the object sinking into the surface | | Tension | $T$ | Along the rope or string, pulling on the object | Same size along a light rope over a smooth pulley | | Friction | $f$ | Parallel to the surface, opposing sliding or the tendency to slide | Static friction adjusts up to a maximum; kinetic friction acts once sliding | | Air resistance or drag | $F_{drag}$ | Opposite to the velocity | Grows with speed | | Thrust or applied force | $F$ | As applied | Engine, person, rocket | Mass is the amount of matter and is measured in kilograms and does not change with…