Distance

Distance travelled is the total length of the path an object covers as it moves, measured in metres, kilometres, or any other unit of length. When something moves at a steady speed, the distance it covers grows in direct proportion to how long the journey lasts and how fast it goes: double the time or double the speed, and you double the distance. Unlike displacement, distance ignores direction entirely and never decreases, so a car that drives out and returns home has travelled a real distance even though its net change in position is zero. It is one of the most intuitive quantities in physics because we experience it every day, from a walk to the shops to a flight across a continent.

We rely on distance constantly in practical life: planning a road trip and estimating fuel, reading the odometer in a vehicle, tracking steps or kilometres on a fitness watch, or working out arrival times for deliveries and travel. Engineers and navigators use the same simple relationship between speed and time to design timetables, calibrate speedometers, and calculate stopping distances for safety. Because it is so easy to grasp and measure, distance is often the first step in understanding motion before adding the complexity of direction, acceleration, or changing speed.