Friction is the resistance between contacting surfaces when they move. It provides traction needed for walking without slipping. About 20% of automobile engine power is consumed overcoming frictional forces
Contact mechanics studies deformation of solids touching at one or more points. Normal stress acts perpendicular to surfaces, shear stress acts tangentially. Normal contact mechanics focuses on frictionless contact and adhesion. Frictional contact mechanics emphasizes effects of friction forces
Friction opposes relative motion between systems in contact. Friction is parallel to contact surfaces and always opposes motion. Friction is proportional to normal force but not contact area
There are six types of spin in table tennis: backspin, topspin, sidespin, mixed spin, cork spin, and no-spin. Backspin is easiest to create and travels slowly, making it ideal for choppers. Topspin is favorite spin, causing Magnus effect, making it land more on table. Sidespin is used in serve, creating difficult returns and curved shots. Mixed spin combines different types, requiring different racket angles
Magnus Effect creates pressure difference between spinning and non-spinning objects. Named after German physicist Gustav Magnus, who first investigated it. Isaac Newton discovered its cause while watching tennis matches
Power screws convert rotary motion into linear motion and transmit power. Consists of threaded shaft and matching nut with different materials. Can be made from carbon, alloy, or stainless steel