Chapter 7, Problem 44A

Hold your hand like a flat wing outside the window of a moving vehicle. Then tilt it slightly upward and your hand will rise. Explain this in terms of Newton’s third law.

To determine

To explain:The given situation in terms of Newton’s third law.

Explanation of Solution

Introduction:

Force is exerting on body when fluid is flowing around the body. When passenger keep his hand horizontally outside the window of car, the force due to air exert on it. There are two component of that force namely lift and drag force. The component of force perpendicular to the oncoming fluid direction is lift force while parallel to the direction of fluid is drag force.

If passenger hold his hand outside the window of car horizontally, drag force acts on hand is large as compared to lift force. But when he slightly tilts his hand, lift force is in large extent. Passengers’ hand generates lift by pushing air in downward direction. According to Newton’s 3^rd law of motion, air exert equal amount of force in the opposite direction to that of hand, and this force is nothing but the lift force. Due to this lift force, when passenger tilts the hand, it moves upward.

Conclusion:

Lift force in the upward direction is responsible for the moving of hand in the upward direction.