A camera's shutter speed controls exposure, but it's also a powerful creative tools.
It can convey freeze action, motion, isolate subjects and smooth water, and much more.
This tutorial explain how to create these different effects.
A photo represents an average of light over time.
"shutter speed" is used to describe this duration.
When a scene contains moving subjects, The choice of shutter speed determines which of these subjects will appear frozen and which will appear as a blur.
However, one cannot change the shutter speed in isolation without also affecting the exposure or image quality
The combinations of ISO speed and f-number (aperture) enable a broad range of shutter speeds.
More light enables faster shutter speeds, whereas less light permits slower shutter speeds.
Achieving the intended amount of blur can be challenging. For a certain shutter speed, three* subject traits determine how blurred they will appear:
Speed. Subjects which are moving faster will appear more blurred.
Direction of Motion. Subjects which are moving forward or backward from the camera usually won't become as blurred as those moving left to right
Magnification. A subject will appear blurred if they occupy a greater portion of your frame. Longer focal lengths (zoom) result in more magnification for a given subjects distance, but this also increases the likelihood of blur due to camera shake.
A common application of using shutter speed to convey motion is with moving water.
Shutter speeds of around 1/2 a second or longer can make waterfalls appear silky.
Freezing the motion of splashing water required a shutter speed of 1/400 of a second.
You can also use a slow shutter speed to emphasize a stationary subject amongst movement, such as a person standing still with a moving trains as a background when the shutter speed is as slow as about 1/10 to 1/2 a second.