Four students describe the motion of the same kite. Which description states a velocity?
A car holds its speedometer needle rock-steady at 30 km/h all the way around a bend. Nothing about its motion changed. Or did it?
You've already seen that a velocity has two parts: a speed and a direction. Keep both parts in view. Either one can change on its own.
Take the panels one at a time. The truck in the first panel gets faster each moment. Its speed is changing, so its velocity is changing.
The same truck braking gets slower each moment. Its speed is changing again, so its velocity is changing.
The train runs dead straight at a steady 30 km/h. Its speed holds and its direction holds. Its velocity is constant.
Now the car on the bend. It also holds a steady 30 km/h, but its direction is swinging the whole way around. Same steady 30 km/h as the train: only the direction behaves differently.
So the bend settles the opening question. The speedometer holds steady, yet the car's velocity is changing. Because velocity includes direction, a change in direction is a change in velocity even when speed stays constant.
Motion 1: a gondola climbs its straight cable at a steady 4 m/s. Motion 2: a scooter weaves side to side while holding a steady 4 m/s. Classify each velocity as constant or changing.
Try the test on a runner holding a perfectly steady pace around the curved end of a track. Her speed holds steady, but her direction swings around the curve. Because velocity includes direction, a change in direction is a change in velocity even when speed stays constant. Her velocity is changing.
Now an escalator carrying a passenger up its straight slope at a steady 0.5 m/s. The speed holds steady, and the straight slope keeps the direction fixed. Neither part changes, so the passenger's velocity is constant.
Motion 1: a cyclist braking along a straight lane. Motion 2: a cyclist circling a roundabout at a steady 5 m/s. Classify each velocity as changing or constant.
A car's cruise control holds exactly 25 m/s while the highway sweeps through a long curve. A passenger claims the car's velocity is not changing. Which verdict is right?
A delivery drone flies three legs: (1) it rises straight up at a steady 2 m/s; (2) it turns a corner while holding 2 m/s; (3) it speeds up along a straight path. In how many of the three legs is its velocity changing?
A bus holds a steady 30 km/h for its entire route. Under what condition is its velocity constant over the route?