Forces and Motion

Motion can be described using several key measurements. Speed is how fast something moves (a scalar quantity), while velocity includes both speed and direction (a vector quantity). Objects move at different speeds in everyday life—walking is about 1.5m/s, while a jet plane travels at 200m/s!

When an object's velocity changes, it's accelerating. This happens when it speeds up, slows down, or changes direction. Interestingly, objects moving in a circle (like a satellite orbiting Earth) maintain constant speed but are still accelerating because their direction is constantly changing.

Newton's Laws govern how objects move. The First Law states objects continue in the same state of motion unless acted on by a force (inertia). The Second Law shows force equals mass times acceleration $F=ma$. The Third Law tells us that for every action, there's an equal and opposite reaction.

Did you know? When objects fall, they accelerate at 9.8m/s² due to gravity, but air resistance eventually balances this force, causing them to reach terminal velocity where they stop accelerating.

Stopping distances for vehicles combine thinking distance (while the driver reacts) and braking distance (while the brakes slow the car). Many factors affect this, including weather conditions, tyre quality, and whether the driver has consumed alcohol. When braking, kinetic energy decreases as the temperature of the brakes increases due to friction.

Momentum $p=mv$ is another important vector quantity in physics. In collisions, momentum changes over time, creating force. That's why cars have crumple zones—they extend the time of impact, reducing the force and potential damage.