When a body is placed in a liquid in the state of rest, it experience a upthrust and it is called static lift. If the resultant force is experienced a body in a fluid obviously in the state of motion then it is called dynamic lift.
Dynamic lift is the force that acts on a body, such as airplane wing, a hydrofoil or a spinning ball, by virtue of its motion through a fluid. In many games such as cricket, tennis, baseball, or golf, we notice that a spinning ball deviates from its parabolic trajectory as it moves through air. This deviation can be partly explained on the basis of Bernoulli’s principle.This can be explained under three different conditions as shown below.
1. Ball moving without spin: The figure a shows the streamlines around a non spinning ball moving relative to a fluid. From the symmetry of streamlines it is clear that the velocity of fluid (air) above and below the ball at corresponding points is the same resulting in zero pressure difference. The air therefore, exerts no upward or downward force on the ball.
2. Ball moving with spin: A ball which is spinning drags air along with it. If the surface is rough more air will be dragged. Figure b shows the streamlines of air for a ball which is moving and spinning at the same time. The ball is moving forward and relative to it the air is moving backwards. Therefore, the velocity of air above the ball relative to it is larger and below it is smaller. The stream lines thus get crowded above and rarified below.
This difference in the velocities of air results in the pressure difference between the lower and upper faces and their is a net upward force on the ball. This dynamic lift due to spinning is called Magnus effect.
Aerofoil or lift on aircraft wing: Figure c shows an aerofoil, which is a solid piece shaped to provide an upward dynamic lift when it moves horizontally through air. The cross section of the wings of an aeroplane looks somewhat like the aerofoil shown in figure c with streamlines around it. When the aerofoil moves against the wind, the orientation of the wing relative to flow direction causes the streamlines to crowd together above the wing more than those below it. The flow speed on top is higher than that below it. There is an upward force resulting in a dynamic lift of the wings and this balances the weight of the plane.
Hydrostatics topics :
Torricelli's theorem
Blood flow and heart attack
Stream line flow
What is pressure ?
Pressure variation with depth
Pascal's Law
Dynamic lift is the force that acts on a body, such as airplane wing, a hydrofoil or a spinning ball, by virtue of its motion through a fluid. In many games such as cricket, tennis, baseball, or golf, we notice that a spinning ball deviates from its parabolic trajectory as it moves through air. This deviation can be partly explained on the basis of Bernoulli’s principle.This can be explained under three different conditions as shown below.
1. Ball moving without spin: The figure a shows the streamlines around a non spinning ball moving relative to a fluid. From the symmetry of streamlines it is clear that the velocity of fluid (air) above and below the ball at corresponding points is the same resulting in zero pressure difference. The air therefore, exerts no upward or downward force on the ball.
2. Ball moving with spin: A ball which is spinning drags air along with it. If the surface is rough more air will be dragged. Figure b shows the streamlines of air for a ball which is moving and spinning at the same time. The ball is moving forward and relative to it the air is moving backwards. Therefore, the velocity of air above the ball relative to it is larger and below it is smaller. The stream lines thus get crowded above and rarified below.
This difference in the velocities of air results in the pressure difference between the lower and upper faces and their is a net upward force on the ball. This dynamic lift due to spinning is called Magnus effect.
Aerofoil or lift on aircraft wing: Figure c shows an aerofoil, which is a solid piece shaped to provide an upward dynamic lift when it moves horizontally through air. The cross section of the wings of an aeroplane looks somewhat like the aerofoil shown in figure c with streamlines around it. When the aerofoil moves against the wind, the orientation of the wing relative to flow direction causes the streamlines to crowd together above the wing more than those below it. The flow speed on top is higher than that below it. There is an upward force resulting in a dynamic lift of the wings and this balances the weight of the plane.
Hydrostatics topics :
Problems on Bernoulli's theorem and Its Applications
Venturi meterTorricelli's theorem
Blood flow and heart attack
Stream line flow
What is pressure ?
Pressure variation with depth
Pascal's Law
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