What is Magnus Effect?
We all love to play with a ball, so when we throw a ball, it deviates from its original path instead of making a projectile motion. So, the deviation of this ball is called the Magnus Effect.
The Magnus Effect is an observational phenomenon that is closely related to spinning objects traveling via air or a fluid.
When we see an airplane flying in the sky, a question comes to our mind: how do wings take a lift? Is there something that lifts the wings up? Yes, there’s a force that lifts the wings of a plane.
How Wings Take Lift?
The two examples we discussed above are Dynamic Lift and Magnus Effect applications, and now we will discuss these in detail.
Airfoil technologies have drastically changed the way we live. This technology drives gas turbines, flying wind turbines, and hydraulic machines.
An airfoil is a shape that has revolutionized the world of Engineering Physics. An airfoil is a shape that produces a lift when fluid is forced over it. So, what is the source of this lift?
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According to Bernoulli’s principle, the particles at the upper surface should travel more distance than those at the lower surface.
Since the particles at both the surfaces need to reach the end-point simultaneously; therefore, the velocity of upper particles should also be greater than the lower one, as it has to cover a greater distance; this means that the pressure at the top is lesser and at the bottom is high. This pressure difference generates lift.
The argument we discussed above is called the Equal-time argument. However, this was proved wrong, as the particles on the upper and the lower surface can’t reach simultaneously; also the path wasn’t streamlined.
We can see that the high pressure brings the curvature in the fluid flow, as we can see in Fig. So, the more is the curvature, the more is the lift.
Now, we will apply Newton’s third law to understand How Wings Take Lift?
We can see that airfoil pushes the fluid downward, so according to Newton’s third law, the air also generates an equal and opposite reaction force on the airfoil, which results in the lift.
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What is a Dynamic Lift?
We understood how wings take the lift. Now we will study the science behind it.
While seeing an airplane, we ask ourselves why the wings of a plane are at a certain angle; for that, let’s take a look at a new figure:
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The wing of a plane is at a slight angle, and this causes the air streamlines at the upper surface group together, as shown below:
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We can see that the area between the streamlines has reduced a bit. So, by Bernoulli’s Principle, the mathematical expression for the same will be:
A1V1 = A2V2……..(1)
This equation is called the continuity equation.
Here,
A1 is the area between the streamlines at the upper surface
V1 = Flow velocity of the streamline at the upper surface
A2 = area between the streamlines at the lower surface
V2 = Flow velocity of the streamlines at the lower surface
What happens here is, as the space or gap between the streamlines reduces, the velocity increases. From expression (1), we can understand that the area is inversely proportional to the streamline’s velocity, i.e., high velocity, low pressure and low velocity, high pressure.
Now, considering the direction of the wings and the air molecules. If the wings are traveling in the positive x-direction, and the air molecules are rushing past to the wings.
So, if we take the reference frame of the wing, then we are going to have streamlines of air that will rush in the direction of air molecules along the x-axis.
Since the direction of the wing is along the direction of motion, along the x-axis and also they are bent by some angle, that’s why the streamlines at the upper surface come close to each other and are separated at the bottom surface of the airfoil.
So, from equation (1), we understood that the pressure difference creates an invisible force, which acts along the y-direction, and that force is nothing but the lift. This lift is known as the Dynamic Lift.
Mathematically, we can express the Dynamic Lift as:
F = ΔPA…..(2)
So, what is Dynamic Lift? It is a force that lifts our wing, and therefore, lets our plane continue flying in the air.
Summary
We understood from the above explanation that area reduction between the streamlines increases the velocity, and from the continuity equation, when the area decreases, the volume increases; this, in turn, increases the flow velocity of the streamline at the upper surface. Since the velocity at the upper surface is higher, that’s why the pressure will be lower, while at the lower portion, it will be higher.
As the difference arises, there is a force that lifts the wings and helps the plane continue its flight.
FAQs on Dynamic Lift
1. What is dynamic lift in Physics?
Dynamic lift is the force that acts on a body, such as an aeroplane wing or a spinning ball, in a direction perpendicular to the flow of the fluid around it. This lift is generated because of a pressure difference between the different surfaces of the object, which is caused by the fluid moving at varying speeds.
2. How does Bernoulli's principle explain the lift of an aeroplane's wing?
According to Bernoulli's principle, where the speed of a fluid is higher, its pressure is lower. An aeroplane's wing, also called an aerofoil, is designed so that air travels faster over its curved top surface than its flatter bottom surface. This creates lower pressure above the wing and higher pressure below it, resulting in a net upward force, which we call dynamic lift.
3. What is the main difference between lift and drag?
Lift and drag are both aerodynamic forces, but they act in different directions relative to the object's motion through a fluid like air.
- Lift is the force that acts perpendicular to the direction of motion, keeping an object airborne.
- Drag is the resistance force that acts parallel to and opposite the direction of motion, slowing the object down.
4. Can you give some real-world examples of dynamic lift?
Yes, dynamic lift occurs in many everyday situations beyond just aeroplanes. Some common examples include:
- The 'swing' or curve of a spinning cricket or baseball.
- The sharp dip or curve of a spinning tennis ball, known as the Magnus effect.
- The upward force generated by the rotating blades of a helicopter.
- The way a simple kite flies by deflecting wind downwards.
5. Why is the top surface of an aeroplane wing curved?
The top surface of a wing is curved to make air travel a longer distance in roughly the same amount of time as the air travelling along the flatter bottom surface. To cover this longer path, the air on top must move faster. This increased speed leads to lower pressure on the top surface, which is the fundamental reason why lift is generated.
6. How does a spinning ball experience a sideways lift, also known as the Magnus Effect?
When a ball spins, it drags a thin layer of air with it. On one side, this dragged air moves in the same direction as the airflow, increasing its overall speed. On the opposite side, it moves against the airflow, slowing it down. This speed difference creates a pressure imbalance, resulting in a net sideways force (a form of dynamic lift) that causes the ball to curve in flight.
7. What are the four main forces that act on an aeroplane during flight?
The four primary forces acting on an aeroplane are:
- Lift: The upward force that opposes gravity and keeps the plane in the air.
- Weight: The downward force of gravity acting on the plane's mass.
- Thrust: The forward force generated by the engines to move the plane.
- Drag: The backward force of air resistance that opposes thrust.
8. What is the general formula used to calculate the force of lift?
The general formula for calculating the lift force (L) is given by the lift equation: L = ½ × ρ × v² × A × CL. In this formula:
- ρ (rho) stands for the density of the fluid (air).
- v is the velocity of the object.
- A is the surface area of the wing.
- CL is the coefficient of lift, which depends on the object's shape (the aerofoil) and its angle of attack.
