My girls and I rooted on Dana Vollmer of the US as she set the world record in the 100-m butterfly with a time of 55.98 s. My younger daughter, age 6, said during the race, "They don't seem to be going that fast." Perspective is everything! To fully appreciate those elite athletes in action, cameras move with the swimmers so that we have an idea what the stroke action is like. Moving along in someone's reference frame obviously makes it difficult to appreciate how fast that person moves with respect to the Earth's surface.
I asked my daughter if she could walk faster than Vollmer was swimming. My daughter said, "Yes!" Maybe, but then again, maybe not. Average walking speed is roughly 5.0 km/hr (1.4 m/s or 3.1 mph). Very young children and older people walk within 0.5 km/hr or so slower than that; fit teenagers and adults within 0.5 km/hr or so faster than that.
How fast was Vollmer? Without getting too technical and analyzing the details of the entire race, simply calculate her average speed. Covering 100 m in a time of 55.98 s gives an average speed of 1.786 m/s, which is 6.431 km/hr or 3.996 mph. That speed is actually a bit slower than power walking, which is around 8.0 km/hr (2.2 m/s or 5.0 mph). My 6-year-old daughter is not likely to keep up with Vollmer's record-setting butterfly pace -- unless she started to jog.
Don't be fooled by cameras moving along with elite swimmers. Those athletes can fly!