Creating movement in flat, still artwork has been explored heavily since the invention of photography and motion pictures (which are just many, many flat, still images being shown in a very rapid sequence).
Artists have implied motion in art in a variety of ways- blurring of detail, using multiple frames, repetition of lines and shapes, overlapping, directional lines, and changes in value.
This painting by Giacomo Balla demonstrates a number of these elements. There is a repetition of the moving body parts and shapes. There is a lot of overlapping. I point out to the students that you can make something look fast by repeating it many times, or slow by repeating it only a few times. Students identify what is the fastest thing and slowest thing in the painting.
There is a change in value throughout the moving parts. Particularly in the woman's lead foot. You can see how the value is dark at one end of the repetition and light on the other end. This implies a beginning of the action and an end to it. Past and present.
Another example of these elements is Duchamp's Nude Descending a Staircase. Repetition. Check. Overlapping. Check. Value change? Check. Even though this is a more abstract example, there is obvious implied motion in the painting.
When students do their images showing motion they must repeat a shape at least 3 times and use at least 3 steps of color value change. The subject matter is up to them. I show them examples I have done, but I emphasize the importance of applying these elements in an original way. I have students brainstorm and write a short list of things that could move and then make small sketches of 2 of those ideas. They then pick the best one to execute on watercolor paper.
Students have used watercolors to complete this project. By the time they do this project with me they have already created tints with colored pencils and crayons, so it gives them practice in creating tints by adding more water to a color to make it lighter and lighter.