01Distance and displacement
Distance is the total path length an object travels. It only has a size (a number) — for example, 400 m.
Displacement is different: it is how far an object is from its start point, in a straight line, and in which direction. A quantity with both size and direction is called a vector.
02Speed and velocity
Speed tells us how fast something moves. It only needs distance and time.
Velocity is speed in a stated direction. Two cars can have the same speed but different velocities if they travel different ways.
03Acceleration
Acceleration is how quickly velocity changes. An object accelerates if it speeds up, slows down (this is sometimes called deceleration), or changes direction.
04Reading motion graphs
On a distance–time graph, the steepness (gradient) of the line shows speed. A flat line means the object is not moving.
On a speed–time graph, the gradient shows acceleration, and the area under the line shows the distance travelled.
- Steep upward line = fast speed / large acceleration
- Flat horizontal line = constant speed, OR zero acceleration
- Downward line on a speed–time graph = slowing down
| Term | 한국어 | Meaning |
|---|---|---|
| distance | 거리 | Total path length travelled |
| displacement | 변위 | Straight-line distance and direction from the start |
| speed | 속력 | Distance moved per second |
| velocity | 속도 | Speed in a stated direction |
| acceleration | 가속도 | How fast velocity changes |
| gradient | 기울기 | The steepness of a line on a graph |