The document discusses several key mechanical principles: - Resistance can help or hinder movement depending on the situation. Air resistance slows runners at the end of a sprint. - Transferring weight is important for generating power and distance in activities like badminton and discus throw. - Propulsion in water sports like swimming involves using arms and legs as levers to push against the water. - Force and friction can both help and hinder depending on the situation. Friction from studs helps footballers but ice skaters try to reduce friction.