Describe the most favorable horizontal and vertical forces. In cross-country skiing, the skier slides forward first on one ski and then on the other. The ski bottoms are coated with special waxes so they exhibit large static frictional forces on snow but small dynamic frictional forces. Modern tracks are often constructed out of recycled rubber tires. The track surface is very resilient, deforming slightly when you push down on it and then bouncing back when you stop pushing.
Bicyclists now use aerodynamically designed bicycles and clothing to minimize air drag.
Use physics to explain why a tail wind gives a runner a time advantage. You are consulting for a screenwriter who is working on a science-fiction movie about the crew of a large, intergalactic spaceship. She wants the script to be realistic from a scientific perspective so she has asked you to check her work so far. You read through the script, which includes descriptions of special effects, and quickly find several problems with it. Here are some of the scenes that have flaws.