why do ping pong paddles have two different sides
Table tennis racket Table tennis regulations approved by the International Table Tennis Federation (ITTF) allow different surfaces on each side of the paddle for various amounts of spin (including nullifying it) or speed.[1] For example, a player may have a spin-heavy rubber on one side of his paddle, and no spin on the other side. The player can flip the racket in play for different types of returns. To help a player distinguish between different types of rubber used by his opponent, regulations specify that one side of a paddle must be red while the other must be black, allowing a player to see what side of a paddle hits the ball mid-play. The player has the right to inspect his opponent's racquet before a match to see the type and color. Current rules state that, unless damaged in play, the paddle cannot be exchanged for another at any time during a match.[2]
Rudder On an aircraft, the rudder is a directional control surface along with the rudder-like elevator (usually attached to the horizontal tail structure, if not a slab elevator) and ailerons (attached to the wings) that control pitch and roll, respectively. The rudder is usually attached to the fin (or vertical stabilizer), which allows the pilot to control yaw about the vertical axis, i.e., change the horizontal direction in which the nose is pointing. The rudder's direction in aircraft since the "Golden Age" of flight between the two World Wars into the 21st century has been manipulated with the movement of a pair of counter-moving foot pedals by the pilot, while during the pre-1919 era rudder control was most often operated with by a center-pivoted, solid "rudder bar" which usually had pedal and/or stirrup-like hardware on its ends to allow the pilot's feet to stay close to the ends of the bar's rear surface.