To freeze it · sharp enough
1/200s
The setting on the dial. The maths says 1/170s, and this is the next one up.
To blur it · clearly moving
1/8s
Track the subject through the frame and fire — it stays sharp, everything behind it runs. Continuous drive, and keep turning after the shutter closes.
Viewfinder
The slow shutter with the camera held still: the subject moves while the shutter is open, and comes out smeared.
A photo collects light for as long as the shutter is open. If the subject moves in that time, it is recorded at every point along the way, so it comes out smeared. A faster shutter gives it less time to move. Follow it with the camera instead, and the subject holds still in the frame while everything behind it smears.
Where the subject is
To scaleThe whole width of the picture, measured where the subject is, and how far the subject moves while the shutter is open. Inside the dashed mark it still looks sharp.
picture 5.1 m wide at 5 m
moves 18 cm in 1/8s · sharp allows 8.2 mm