Scientific Questions

Nevermind, I got that question myself, release all our muscles meaning untightning it and giving all of my force a focus by simply following it through the muscle!(its ok if you don't get it...coz I do)

ffx-me wrote: side spin, same principle as why the ball drops with topspin.  When the ball travel through the air we can look at the ball as being still with the fluid, air, moving around it.  the faster a gas moves the lower the pressure.  if the ball travels and spins, one side spins with the air flow and there is no effect but on the otherside the ball spins in the opposite direction and grips a bit of air making the airflow slower on that side and therefore there is a lower pressure on the other side.  naturaly there is a force applied on the ball towards the lowest pressure and the ball curves.  Planes fly using the same principle.

Nice...fatt....I have been struggling to get this since months...and you make it sound so simple!(did you major in physics?)

gulca wrote: If the path of flight is the same as the axis of rotation, you do not see this effect.

SIDOFMILENIUM wrote: gulca wrote: If the path of flight is the same as the axis of rotation, you do not see this effect.   Can you give us an example?   Alright...I got another one for you guys....why does a slower blade spins the ball more?(since the spin depends on how much a blade is able to flex....the thick soft blade should be same as slim soft blade....may be even greater since it won't absorb the spinning pressure!)   Thanks.

You have to look at it like a collision, you apply a force on the ball and there is an impulsion (force in a collision changing the quantity of movement).  And, F=ma  so in order to get more spin the contact time needs to be longer because the acceleration will be longer and we will have a greater jump in velocity (of spin, i dont know the term in english)  Harder bats have shorter dwell times and brush the ball for a shorter time and therefore put less spin.  Of cource if the blade flexes the time will be greater.


Oh and an example of the spin that will not curve (doesnt oppose the movement) is topspin towards the side,

Hmm...I already visited those links...didn't help me...but your words did Anyways...seems like the thicker a softer blade is(faster and heavier)...the spinnier it is b/c the less torque it absorbs...tell me if I am right....Therefore, the saying that slower the wood, faster it is, that is just a myth.(true in some cases obviously)

fatt wrote: SIDOFMILENIUM wrote: Nice...fatt....I have been struggling to get this since months...and you make it sound so simple!(did you major in physics?)       If I had a physics degree you would not have understood my answer   I got answers from those 2 websites:   http://www.gregsttpages.com/articles/tt_physics_maths.html scroll down until you see the yello ball  after the question: "Why does spin behave the way it does?" it's from Greg Lett's website; you know that guy who's running tt about dot com. That website is not much moving since he took over about tt dot com. He moved the article though: http://tabletennis.about.com/od/basicconcepts/ss/spin_in_tt.htm http://tabletennis.about.com/od/beginnersguide/a/physics_mathsTT_2.htm   Also this is really cool: http://www.unc.edu/~sheng1/spin.htm

I'd just like to point out that the physics in the sections labeled "Why does spin behave the way it does?" and "Why a new ball is preferable to an old one" are completely wrong.  Actually, I just read the entire article again and, while there are a few correct ideas, most of that article is complete garbage as far as physics goes.

fatt wrote:  the slower the blade the spinnier it is: YES. I think it is the same idea than softer or harder sponge. When the sponge is softer, it's easier for the ball to sink into the sponge and the forearm moving while the ball is sinking into the sponge creates spin. Same idea with a slower blade:  the ball will stay with the blade and in the sponge a longer time instead of bouncing back right away so more spin is created.   By the way: you can still create a lot of spin with the faster blade; you just need to have a much higher arm speed to have the ball stay long enough with the paddle and in the sponge.

raptor3x wrote:   ...... I'd just like to point out that the physics in the sections labeled "Why does spin behave the way it does?" and "Why a new ball is preferable to an old one" are completely wrong.  Actually, I just read the entire article again and, while there are a few correct ideas, most of that article is complete garbage as far as physics goes.

Mithrra,

Your conservation of energies are explained incorrectly.

Comparing a ball with a plane doesn't make sense. Shape of the plane is design to have maximum efficiency flying forward. That doesn't mean that a sphere ball cannot share the same effect of lift.

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imagine a stationary ball in midair spinning without any gravity. How does one tell which side is up and which side is down? How do you apply force? Which side is faster? Slower? There is no difference if the ball isn't moving in some direction.

A ball traveling along it's spinning axis will have no Bernoulli effect. I believe it is a pure corkscrew spin traveling towards the opponent will give this effect (ignoring gravity).

magnus effect?

Mithrra,

You mixed up energies, force, velocity, spin and gravity. Please do not confuse others with your own confusion.

My description of a stationary ball spinning is just an example to show there is no top nor bottom left or right. You do have the axis of rotation. But other than that, you cannot say if the ball is spinning left or right, top or bottom, underspin or topspin. The ball needs to be moving in some direction.

Bring this up with any physics professor or any science major. They will sort you out.

But please, do not spread false scientific explanations to the less educated.

Mithrra
I'll let others have a say on your explanation.

I do agree learning your mistake is progress. However spreading confusion to others while you learn isn't nice.

I apologize if I seem to be attacking you. I am not.

Find some physics teacher and have them listen to your explanation. If they agree with you, then I must be the confused one.

As for other comments made, the law of conservation of energy and the law of conservation of momentum have been skewed as well.

with regards to conservation of energy:
 - gravitational potential energy (PE) is given by mass*force of gravity(9.8m/s^2 on Earth)*height. Symbolized mgh
 - Translational Kinetic energy = 1/2*mass*velocity squared. Symbolized 1/2mv^2
 - Rotational Kinetic energy will be more complicated to understand on paper but is derived from moment of inertia (like mass but has to do with how easy it is to start something spinning)*angular velocity squared. Symbolized I*omega^2 (sorry i don't have the greek symbol on my keypad)

If we account for work done from non conservative forces (things like friction, sound and heat where energy is dissipated) energy is conserved in a system which can be show by this equation:

PE before + KE(rotational) before + KE(translational) before + work before = PE after + KE(rotational) after + KE(translational) after + work after.

Stay with me now. This simply means that if you have a ball and drop it from a cliff, the potential energy that it had at the top of the cliff, given by mgh, is directly proportional to its kinetic energy and thus velocity (remember KE(translational)=1/2mv^2). Work would account for energy lost due to wind resistance and also explains terminal velocity)

This is a lot of info to try and explain in a couple words so it would probably be better to take a class or talk to a physics professor in person. The point I'm trying to make here is that when you put work into the system of the ball by hitting it with your paddle, it is translated into rotational kinetic energy, translational kinetic energy, and for lobbers, potential energy (which is actually insignificant because the mass of a ping pong ball is so small, PE=mgh)

You could also take into account the potential spring energy stored in the sponge and rubber of your paddle but is not really necessary in this explanation.

now that i think about it i don't really want to take the time to explain conservation of momentum (mass1*velocity1=mass2*velocity2), or newtons second law (Sum of the forces = mass*acceleration). I can't remember the specific points that were mentioned earlier and don't want to take the time to go back and read all the posts but if you have a question or something, go ahead and I'll do my best.

" To remain silent forever is a forever fool,

   To be humble & honest to ask is a wise man's deed"