A physics worksheet shows a toy car on a circular track, drawn from above, moving at a steady speed. Two arrows sit on the car: one labeled velocity, one labeled acceleration. One of the two arrows is drawn wrong.
Which arrow is wrong, and how can you tell?
A circular-motion diagram makes two claims, and each claim can be checked.
Check the velocity arrow first. The velocity lies on the tangent, the line that just touches the circle at the object's position, and it points the way the object travels.
So a velocity arrow that points toward the center, away from the center, or against the stated direction of travel is wrong.
Check the acceleration arrow next. The acceleration points from the object toward the center of the circle, at every point.
So an acceleration arrow that points away from the center is wrong, however tidy the diagram looks.
The worksheet's car: its velocity arrow lies on the tangent and points the way the car travels, so it passes. Its acceleration arrow points away from the center, so that arrow is the wrong one.
The diagram shows a drone flying a circle at a steady speed, clockwise as drawn on the page. One arrow is drawn: the acceleration. Is the acceleration arrow drawn correctly?
The diagram shows a marble rolling in a circular groove at a steady speed, counterclockwise as drawn on the page. One arrow is drawn: the velocity. Is the velocity arrow drawn correctly?
The diagram shows a cyclist riding a circle at a steady speed, clockwise as drawn on the page. Kaia says: the velocity arrow is wrong, because the velocity lies on the tangent, and only the acceleration points toward the center. Is she correct?
A diagram shows a scooter at the lowest point of a circle, moving counterclockwise as drawn on the page, at a steady speed. The velocity arrow points to the right. The acceleration arrow points straight up. Judge both arrows.
At the lowest point of a counterclockwise circle, the tangent runs left to right, and the travel is to the right. The velocity arrow points right, so it passes.
The center of the circle sits straight up from the lowest point. The acceleration arrow points straight up, toward the center, so it passes.
Both arrows are drawn correctly.
The diagram shows a toy train on a circular track at a steady speed, clockwise as drawn on the page. Which arrow, if any, is drawn incorrectly?
The diagram shows a skater circling a rink marker at a steady speed, counterclockwise as drawn on the page. Which arrow, if any, is drawn incorrectly?
The diagram shows a go-kart on a flat circular course at a steady speed, clockwise as drawn on the page. The course owner asks whether the diagram can go on a poster as drawn. Which arrow, if any, is drawn incorrectly?