Two friends leave the same school door, each walking at a steady 2 m/s. Ten minutes later they are 2400 m apart. Knowing exactly how fast each friend walked, you still could not have said where either one ended up.
In earlier grades you saw speed: how fast something moves. A speed of 2 m/s says the walker covers 2 meters each second. It says nothing else.
The missing piece is direction. One friend walked east at 2 m/s; the other walked west at 2 m/s. In 600 s that is 1200 m each way, and 2400 m apart. Same speed, opposite journeys.
A description that tells you both, how fast an object moves and in which direction, is called a velocity. 2 m/s east is a velocity.
A description that tells you only how fast is a speed. 8 m/s by itself is a speed.
Statement 1: 'The train moved at 20 m/s.' Statement 2: 'The train moved at 20 m/s toward the coast.' Classify each statement as giving a speed or a velocity.
Run the test on a boat crossing a lake at 6 m/s toward the north shore. The description tells how fast the boat moves: 6 m/s. It also names a direction: toward the north shore. How fast plus a direction is a velocity.
Four students describe the motion of the same kite. Which description states a velocity?
Now a hardware-store label: the saw's chain moves at 18 m/s. The description tells how fast the chain moves, and no direction is named. How fast alone is a speed.
A diver's wrist computer logs '0.5 m/s, downward.' Her teammate radios the surface: '0.5 m/s.' Classify each report as giving a speed or a velocity.
A ship's captain radios the harbor: 'engines steady, making 10 m/s.' The harbormaster replies that she still cannot chart where the ship will be in one hour. What is the report missing?
Two airliners each fly at a steady 250 m/s. Must the two airliners have the same velocity?
A hot-air balloon drifts at 3 m/s toward a radio mast. A student writes: 'the balloon's speed is 3 m/s toward the mast.' What is wrong with the student's sentence?