When a ball spins to left, shouldn't it curve right?(hurricane vise)

[rcgldr]

There is an alternate and probably more accurate explanation of Magnus Effect. As I mentioned previously, there is only a very thin layer of air that spins with the ball. I had explained that this spinning air contributed to a pressure differential because of reactions at the front of the ball, but the following article in the link below states that it's a more a reaction at the rear of the ball, (although the included drawing shows deflection starting from in front of the ball), in that the thin layer of spinning air just disrupts the air flow past the ball, causing the flow to detach on the forward spinning surface sooner than the backwards spinning surface, and the result is that the air flow is deflected (accelerated) in the same direction as surface movement at the back half of the ball (back spin would cause downwards acceleration), and the air reacts with an opposing force. The picture in this article gives a much better idea of what is happening than the Wiki article, since it clearly shows (although exagerated) the deflection of air flow.

Magnus Effect .htm

It's my belief that the Magnus effect is a combination of what I described previously and the separation of air flow as mentioned in the article linked to in this post. Since the layer of spinning air around the ball is very small, probably most of the Magnus Effect is due to the air flow separation occurring earlier on the forwards spinning surface and staying "attached" longer on the backwards spinning surface.

 

[Skhandelwal]

"If the ball has backspin, then the bottom surface of the ball is moving forwards faster, and the top surface of the ball is moving forwards slower"

How can one part of the surface be moving faster than another? To me it is similar to the analogy of 2 cars traveling at the same speed but one approaches the red light first b/c it was ahead to begin w/.

"The bottom surface of the ball accelerates the air forwards a bit more than the non-spinning case, and top surface of the ball is accelerating air forwards less than the non-spinning case."

how? I like to look at this as an analogy of a ball spinning underwater...if it is spinning fast enough...it will create a whirlpool...but why would it create a whirlpool-I don't know.

"in the case of backspin). The greater the acceleration, the higher the pressure because of the air's momentum and resistance to acceleration. So the differential in acceleration of air corresponds to a differential in reactive pressure, higher pressure below, and lower pressure above. Air can't flow through the ball, so there's a net downwards acceleration of the air because of the pressure differential, and the air reacts with an opposing upwards force on the ball, "lift"."

In backspin, the ball "drops", in topspin, the ball "lifts" so may be you got it mixed up here...or is it me?

"Air "attaches" to the ball because of friction between the air and the ball. This boundary is not infinitly thin, because of "friction" within the air itself, called viscousity. The result is a small amount of air that spins in the same direction as the ball, diminishing with distance from the surface of the ball."

"Are you talking about the negligable air molecules that fall into the little uneven holes on the surface of the ball and keep bouncing from one side to another, till they bounce up and escape? Wouldn't those be extremely temporary?"

These are from the previous post of yours...let me try to understand that basic funda...then I'll move onto the full Magnus Effect explanation.

 

[rcgldr]

"If the ball has backspin, then the bottom surface of the ball is moving forwards faster, and the top surface of the ball is moving forwards slower"

How can one part of the surface be moving faster than another? To me it is similar to the analogy of 2 cars traveling at the same speed

How about the tires of a car? The bottom part of the tire isn't moving with respect to the road, but the top part is moving at twice the speed that the car is, with respect to the road.

"The bottom surface of the ball accelerates the air forwards a bit more than the non-spinning case, and top surface of the ball is accelerating air forwards less than the non-spinning case." how? I like to look at this as an analogy of a ball spinning underwater...if it is spinning fast enough...it will create a whirlpool...but why would it create a whirlpool-I don't know.

It's called Coanda effect, friction between the surface of the ball and air, and within the air itself (called viscosity), cause a thin layer of air to spin with the ball, diminishing quickly with distance from the surface of the ball.

In backspin, the ball "drops", in topspin, the ball "lifts"

It's the other way around, backspin can cause a ping pong ball to rise if there's enough spin and speed, top spin causes the ball to drop. Top spin allows the ball to be struck for more forwards speed, because the ball will clear the net and still drop enough to contact the other side of the table. Note how the ball drops and curves from the top spin shots in this short video clip:

tt2.wmv

"Air "attaches" to the ball because of friction between the air and the ball." Are you talking about the negligable air molecules that fall into the little uneven holes

The effect is not negligable. Actually, significantly sized holes can help reduce this effect, which is why golf balls have dimples, to reduce the curvature of the path.

These are from the previous post of yours...let me try to understand that basic funda...then I'll move onto the full Magnus Effect explanation.

The Magnus effect article I linked to states that it's the difference in disruption and detachment of the air stream on either side of a spinning ball that results in a curved path. I'm thinking it's that it's a bit of both, that the thin spinning layer of air both contributes directly to pressure differential at the front of the ball as well as causing a differential in air stream detachment as the ball travels through the air.

The diagram, although exagerrated, has it right, ultimately, the air is deflected perpendicular to the path of the ball because of the balls spin and forwards speed. Using Newton's laws to describe the process, the ball exerts some of it's force on the air perpendicular to the ball's path, and the air responds to this perpendicular component of force with an equal and opposite reaction force as the air is accelerated, causing lift (by definition).

 

[Skhandelwal]

"How about the tires of a car? The bottom part of the tire isn't moving with respect to the road, but the top part is moving at twice the speed that the car is, with respect to the road."

The analogy doesn't help...IDK how the car tires do it either.

"he effect is not negligable. Actually, significantly sized holes can help reduce this effect, which is why golf balls have dimples, to reduce the curvature of the path."

Just out of the blue...is it possible to make a type of ball by putting holes or whatever on it which will make it impossible to curve in air?

I believe the Magnus effect relies on the principles questioned above. So once I understand those...I'll understand the effect too. Btw, I can't thank you enough for doing this...you have changed me in such a way that from now on, I will take pleasure in helping others rather than seeing it as a duty which I try to avoid.

 

[rcgldr]

is it possible to make a type of ball by putting holes or whatever on it which will make it impossible to curve in air?

A very heavy ball, like a shot put won't curve much because of the mass to surface area ratio. It's possible that a perforated wiffle ball, one with holes all around allowing air to flow through would also experience minimum curvature, but I don't think it's possible to eliminate curve in air completely.

 

[beatenbob]

Russ,

First of all, the baseball curves b/c its surface is uneven.
I am talking about a table tennis ball.(high quality ones have internal seam so they are perfectly smooth)

Also, from the article, how come the air hitting the top of the wings of the airplane is faster?

You might have to take look in this article http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html

 

[rcgldr]

You might have to take look in this article http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html

In the first pair of diagrams in that article note that it's a closed system. If the pipe in the first diagram has holes in it then the fluid will flow out of the pipe at higher pressure areas, and into the pipe at lower pressure areas, and the amount of mass flowing across any point in the pipe will vary, requiring a dramatic change to the equations involved.

Regarding faster moving air streams corresponding to lower pressures on a aircraft, note that slower civilian aircraft, like a Cessna, have a hole in the side of the fuselage, which experiences a crossflow equal to the true air speed of the aircraft, yet the pressure at the hole is basically the same as the pressure at the surrounding static air. This hole is called a "static" port, and it's connected to an internal chamber. The pressure of the internal chamber is used to indicate the current altitude, and works regardless of the airspeed (within the range of the air speeds a Cessna experiences (0 to about 150mph).

Read the section regarding static ports, air speed and Bernoulli from this link.

http://home.comcast.net/~clipper-108/lift.htm

The article is a bit confusing since it mentions effects very close to the wing surface such as Coanda effect, but then goes on to show the more accurate description of a wing a an "air scoop" with an effectively very large scoop effect.

 

[Skhandelwal]

Hey Jeff, could you please answer my questions above? Thanks a lot.

 

[Roy Dale]

By definition, the reaction force in the direction that the ball moves, slowing it down, is called drag. The reaction force perpendicular to the direction the ball moves, causing it to curve, is called lift.[/QUOTE]

If there were a reaction force in the direction that the ball moves it would not slow it down it would speed it up. Drag is the aerodynamic force in the direction of the relative airflow that caused it and lift is perpendicular to the relative airflow that caused it. You cannot accurately define lift in relation to the motion of the ball because lift does not require the motion of the ball. And any way you are not determining lift by the direction the ball moves you are determining it by the balls motion through the air, this maybe why you think the ball is generating lift. The ball is generating a relative airflow by its motion through the air and its motion while in the air (rotation). Drag not only opposes the motion of the ball through the air it also opposes its rotation, that’s a lot of directions. If the friction drag (reflected in a torque force that opposes rotation) around a spinning ball were to become greater on one side than the other this force will start to become more linear just like a tire pushed into the ground. The spinning ball is pushed into the air by its forward motion. This effect is not as dramatic as a tire but it is enough to make the ball curve. And because the curve is the result of friction drag any surface preparation that increases friction drag (dimples, fuzz, threads) will also increase the Magnus effect.