Have you wondered how people have photos of waterfalls that look smooth and give the illusion of motion or direction of flow? Maybe you are more concerned with why your wildlife photos aren't crisp, or why a baseball pitch looks blurry? It all comes down to shutter speed and motion blur. Shutter speed is given in increments of seconds, generally a whole 1 is 1 second and any fraction thereafter will be faster than a second (1, 1/250, 1/2000, 1/4000). I have some photos of birds to illustrate the general idea of what the difference in shutter speed might look like.
All of these were captured with the D810 - I have listed the lenses that were being used at the time. Please note that as shutter speed is adjusted, often the ISO is adjusted as well. This goes back to my first blog about the relationship between shutter speed, aperture and ISO. Camera settings also vary depending on how much sunlight is available at the time of the photo.
Let me know what you think in the comments section.