Fergus sketches his slot-car track from above: a circle. His car sits at the top of the drawing. He wants to add the velocity arrow, but the sketch does not yet say which way around the car runs.
Two words settle it. Which way is clockwise, and which way is counterclockwise?
Viewed as drawn on the page, a clock's hands sweep from the 12 position to the 3, down to the 6, over to the 9, and back to the 12. Motion that way around is called clockwise.
Motion the opposite way around, from the 12 position to the 9 to the 6 to the 3, is called counterclockwise.
The two words come with a viewpoint: as drawn on the page. Seen from the other side, the senses swap, so we always read the drawing as shown.
A ride drawing shows a car passing the 12 o'clock position, then the 3 o'clock position, then the 6 o'clock position. Viewed as drawn on the page, which way around is the car running?
With the sense named, drawing the velocity arrow at a point is a routine.
Step 1: draw the radius from the center to the point.
Step 2: draw the tangent at the point: the line perpendicular to that radius.
Step 3: point the arrow along the tangent, the way the stated sense carries the object through that point.
At the top of a counterclockwise circle, the object is heading from the 12 position toward the 9. The arrow points left.
Fergus's slot car runs counterclockwise, and it is at the top of the drawn circle (the 12 o'clock position). Draw its velocity arrow.
Draw the radius: from the center straight up to the 12 o'clock point.
Draw the tangent: perpendicular to that radius, so horizontal.
Counterclockwise carries the car from the 12 position toward the 9, the left side of the drawing.
Point the arrow left along the tangent.
The arrow sits on the horizontal tangent at the top, pointing left.
A different run: the car now runs clockwise, and it is at the 3 o'clock position. Draw its velocity arrow.
Draw the radius: from the center out to the right, to the 3 o'clock point.
Draw the tangent: perpendicular to that radius, so vertical.
Clockwise carries the car from the 3 position toward the 6, the bottom of the drawing.
Point the arrow down along the tangent.
The arrow sits on the vertical tangent at the 3 o'clock point, pointing down.
The bead runs counterclockwise, viewed as drawn on the page, and it is at the 6 o'clock position. Which way does its velocity arrow point?
The cart runs clockwise, viewed as drawn on the page, and it is at the 9 o'clock position. Which way does its velocity arrow point?
The skater travels counterclockwise, viewed as drawn on the page, and she is at the 3 o'clock position. Which way does her velocity arrow point?
The carousel turns clockwise, viewed as drawn on the page, and the pony is at the 6 o'clock position. Which way does the pony's velocity arrow point?
The drone flies clockwise, viewed as drawn on the page, and it is at the 12 o'clock position. Which description gives its correct velocity arrow?