Question

Which of the following statements about lift are false? Check all that apply. Correct answers will increase your score. Incorrect answers will decrease our score. Lift and drag forces are always perpendicular Wing shape is not important for generating lift. Surface roughness doesn't impact the lift force generated by rotating/spinning objects. The area used in the definition of the lift coefficient is usually the planform area of the object (e.g, wings).

Answer 1

(2nd and 3rd statements are false) because wing shape is important for generating lift and surface roughness impact the lift force generated by rotating/spinning objects. For example giving a spin to a tennis ball or making a drop shot on a tennis or ping-pong ball by giving a fore spin in order to alter the lift characteristics and cause the ball to produce a more desirable trajectory and bounce of the shot. Golf, soccer, and baseball players also utilize spin in their games. For a table tennis ball, the distanaces are very short, and the balls never reach the speeds in the turbulent range. Therefore,the surfaces of table tennis balls are made smooth.