fluid mechanics - prepared answers

Question 1

describe what happens when a top spin is applied to a ball (6 points)

Answer 1

1. application of an off centre + eccentric force = creates spin
2. Bernoulli’s principle indicates pressure is inversely proportional to velocity
3. The Magnus effect applies Bernoulli’s principle to explain the effect spin has on the trajectory or flight path of an object
4. top spin = the boundary layer of air on top of the ball clashes with oncoming air particles = creating an area of low velocity and high pressure
5. Underneath the ball, the boundary layer of air is traveling in the same direction as oncoming air particles = creating an area of high velocity and low pressure
6. Objects move from an area of high pressure to low pressure = the ball will be forced downwards. This is a lift force that is known as the Magnus Effect.

Question 2

explain the biomechanics behind how the curveball moves away from a right-handed hitter. (8 marks)

Answer 2

• applies an off- centre or eccentric force to the ball
• magnus force changes the flight path of the ball due to spin while moving through the air
• airflow around the spinning ball (boundary layer) going in same direction as oncoming air creates high velocity
• areas of high velocity form a low pressure system
• airflow around the spinning ball (boundary layer) going in the opposite direction as oncoming air creates low velocity
• areas of low velocity form a high-pressure system
• air moving from hgih to low pressure causes ball to move in same direction
• identifies that the movement of air creates a lift/magnus force

Question 3

explain how Bernoulli’s principle assists in keeping the frisbee in the air longer and thus enhancing the distance it travels (5 marks)

Answer 3

• Bernoulli’s principle states the velocity of fluid flow determines the pressure system ( objects moving through a fluid - fast velocity = low pressure > slow velocity = high pressure)
• high-pressure systems move to the low-pressure systems causing a lift force on the frisbee
• the shape of the frisbee allows low velocity and high pressure to be created underneath and high velocity and low pressure on top
• the angle of attack is required to create lift