Golda's car circles a roundabout at a steady 20 mph. Her speedometer needle sits parked on the 20 the whole way around.
Her speed is not changing. Is her velocity changing?
Velocity is speed with a direction.
Follow the car around. At one moment it heads north. A quarter of the circle later, it heads east.
The speed never moved off 20 mph. The direction never stopped moving.
So an object in uniform circular motion has a changing velocity at every instant, even though its speed is constant.
A delivery truck drives a circular loop road at a steady 30 mph. Is its velocity changing?
It is tempting to call the velocity constant because the speedometer is steady. The speedometer reads only the speed.
The direction is the half of velocity that the speedometer cannot see, and on a circle that half changes without rest.
Constant speed and constant velocity are two different claims. On a circle, the first holds and the second fails.
A jogger rounds a circular park path at a perfectly steady pace, and her velocity is changing the whole time. Why?
Golda's car holds 20 mph around the roundabout. At one marked moment it heads north; a quarter-circle later it heads east. Has its velocity changed between the two moments?
At the first moment the velocity is 20 mph, north.
At the second moment the velocity is 20 mph, east.
The speeds match, and the directions do not.
A velocity is a speed with a direction, so the two velocities are different.
Yes. The velocity has changed, from 20 mph north to 20 mph east.
A toy boat circles a pond fountain at a steady 0.5 m/s, viewed as drawn on the page. At the circle's 12 o'clock position it moves left; at the 6 o'clock position it moves right. Compare the two velocities.
At the 12 o'clock position the velocity is 0.5 m/s, leftward.
At the 6 o'clock position the velocity is 0.5 m/s, rightward.
The speeds match, and the directions are opposite.
The two velocities are different: equal speeds, opposite directions.
Elif says: 'A gondola riding a Ferris wheel at the ride's steady rate has a changing velocity.' Is Elif correct?
A go-kart holds a steady speed around a circular course. Which statement about its motion is correct?
A model train runs a circular track at a steady speed. Which quantity stays constant the whole way around?
Viewed as drawn on the page, a skater glides counterclockwise around a circular rink boundary at a steady 4.0 m/s. At the boundary's 12 o'clock position she moves left; at the 6 o'clock position she moves right. How do her two velocities compare?