frisbee...? Newton's third law..?

Question

before that, i need someone to explain how newton's third law can be applied to lift, since Bernoulli effect has a smaller influence. Since the aerofoil pushes against the air, so what? Wouldnt there simply be a drag force? Where does the lift come from?
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Ok, here's the question i need help with.
1. Why Frisbees fly (i guess i can do it nicely in terms of Bernoulli principle, but i want to know the Newton's way.)
2. Why do Frisbees fly in a more controlled manner when they are spinning.
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Here's a guess for 2. I read beforehand that if u hold the centre of a wheel of a bike and asked someone else to spin it, u will feel a mysterious force if u try to tilt it to anyway. I cant visualize it, but i can understand what they mean by tilting it is changing its direction and so the angular velocity changes, which constitutes a force. Hope there is some way u can help me in my understanding..=)
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(i know its a lot to deal with here, sorry...a good answer gets my ten points)

i understand what lenshure is saying, but that is the explanation for Bernoulli's effect, isnt it?

Answer 1

There is something to be said about the Frisbee lifting itself, but we can get into that later.

The most important thing about a frisbee's flight as anyone who has ever thrown a frisbee can tell you is its spin. The spin establishes the angular momentum of the frisbee which must be conserved throughout the entire flight (yes its rotation does slow down from atmospheric drag). Like a bicycle wheel, this is what keeps the frisbee flying flat and level (if that is how you threw it). Any perturbations in its angular momentum produces torques which act to cancel out that pertubation (just like as you lean into a turn on a bicycle, it attempts to stand you back up).

The frisbee (assuming an entirely round disk) is a rather inefficient airfoil (which by the way, the length of the two surfaces has no actual effect on the lift produced by an airfoil). But will still work the same basic way. The lift produced by an airfoil is caused by the air accelerating around the leading edge of the airfoil (or the rounded edge of the frisbee). As the air encounters the airfoil, it can't go through it so it must flow over it (or under it depending on your angle of attack). Imagine a particle of air approaching the airfoil. As the air particle approaches the airfoil, it can't go through it, so then it accelerates vertically over the airfoil BUT because there is air surrounding that particle, it can't slow down in the horizontal direction. This causes the air to have a net increase in velocity, which causes a decrease in pressure (Bernoulli's Principal).

I haven't actually dont any analysis on the fribee, but the best thing about engineering is the principal of superposition. Basically it states that if you combine any number of known motions, you will end up with the more complex motion (i.e, you know how fast a ball is moving to the left, and you know what it is doing vertically, so if you combine the two you know how it will react).

The rotating frisbee will cause a very slight vortex in the air, but this is nothing to really consider, because if it produced a much more powerful vortex, it would be dragged down and would stop rotating early in its flight, becoming unstable and falling. The important aspect of this is that the rotation will keep the frisbee oriented the same way.

The horizontal velocity of the frisbee, will remain relatively constant throughout its flight (ideally). As it does produce some lift, there will be drag on the disk, causing it to slow down. As it slows, the lift will decrease, causing the frisbee to drop rather slowly towards the end of its motion.

This leads to the next force acting on the firsbee, vertical drag. The bottom of a frisbee is shaped like a parachute, which will resist any motion downwards, and if there is any kind of updraft, will attenuate it.

The curved surface of the frisbee, if thrown at a slight angle upwards, will in addition to imparting extra verticle velocity, generate some lift similar to how an airfoil would. If it is thrown entirely level, most frisbees will still produce a little lift because the surface is cambered (curved).

The combination of these forces would account for the flight of a frisbee

Now if you wanted to look at Newtons third law with this, it would show that forces occur in pairs. If the frisbee is exerting lift, that force has to come from somewhere, which can be seen in the frisbee directing airflow downwards. The drag on the frisbee can be measured by figuring out how much air it is dragging after it. The rotation causing stabilitiy is relatively complex in 3 dimensions, as it is the cross product of its momentum, and the effective radius. This basically gives you a long equation which is the determinate of a matrix. I couldnt find it in the minute I was searching, but if you're not good at calculus, then it wont help you much anyway.

Answer 2

Each ball represents a different mass, which will be the varying factor in how far the ball moves when struck by a putter). Once each student has putted with the three types of balls, the instructor will ask why the students’ feel there was such a difference in how far the balls rolled. The main idea of the lesson is to explain Newton’s Three Laws of Motion. The First Law states that an object in motion remains in motion unless acted upon by an outside force. The Second Law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object. The Third Law states for every action, there is an equal and opposite reaction. The First Law is explained by the fact that the ball does not roll forever. Some of the children will not understand why the ball does not keep rolling. The force that stops the ball from moving is friction. The Second Law is demonstrated by the amount of force the ball is struck with and also the amount of mass in the certain type of ball. This is where the different types of balls will be used. The students will see the difference in how easy or difficult it is to strike the balls. The golf ball will roll very easily due to the fact that it has very little mass. The students will find out that it is more difficult to putt the softball because there is more mass in the softball. Finally, the students will barely be able to get the bowling ball to roll at all. Sometimes, the putter may simply bounce off of the bowling ball due to the fact that it has such a great amount of mass. Newton’s Third Law of motion will be explained when the putter strikes the certain type of ball, there is a reaction, the ball moving forward. In the case of the bowling ball, the putter may not have enough force to move the ball, and therefore, the putter will bounce back. That would be the reaction in that case. Showing how motion and acceleration relate to each other and also applying Newton’s Laws of Motion. Overall, the goal of this lesson is to explain a complex science lesson in an easy to understand lesson.

Answer 3

The aero foil pushes against the air, then as a reaction the air pushes the aero foil.
There is no drag in this case. The Frisbees are moving forward because of momentum and are not moving due to drag ( which is in the case of aeroplanes).
But there is a lift in the frisbee.

You have stated,

“Why Frisbees fly? (I guess I can do it nicely in terms of Bernoulli principle, but I want to know the Newton's way.)”

There is no difference in Bernoulli’s principle and Newton’s third law.

In air , lift is created when air is deflected downward by an airfoil or other body .

The force created by this deflection of the air creates an equal and opposite upward force according to "Newton's laws of motion"

Bernoulli's principle states that in fluid flow, an increase in velociy occurs simultaneously with decrease in pressure.

Or pressure difference corresponds to differnce in squares of velocities

In a fluid flow with no viscosity, and therefore one in which a pressure difference is the only accelerating force, it is equivalent to"Newton's laws of motion".

While applying the bernoullis principle to the lift, we are not bothered, “ why there is a force ( pressure difference)?”

But Newton’s third law tell that the accelerating force is due to the reaction of the deflection of air molecules by the air foil or other body.

About the stability of the Frisbees,
Any spinning object will always tend to keep the direction of axis of rotation unless a torque acts on it.

Answer 4

1. Bernoulli's theorem is in effect that when winds are constricted - pressure and wind speed increase - such as air flowing thought a break in a mountain chain.
In a Frisbee - the air flows faster over the top than the bottom - this creates an area of low pressure in the base of the Frisbee - and air pushes up in response to this low pressure
2. the spin is obviously like a bank that saves energy and slowly expends it as air close to the center bottom of the Frisbee is forced out and then down as it hits the inner edge of the Frisbee. As this air is pushed down near the edge - in the middle air pushes up and helps Bernoulli's theorem to work more effectively

Answer 5

The ' mystery force ' is centripetal force, caused by the inward acceleration of a spinning object.

The frisbee flies better when it spins because of the centripetal force as well as the air underneath it trapped by friction. This air around the frisbee is much smoother than the frisbee.

That is just a wild stab at it. Correct me if I am wrong.

Answer 6

The reason why an air foil works is the top surface of the foil is longer that the lower surface. As the foil moves though the air the air on top of it has to move farther that the air on the bottom. As a result there is a pressure differential between the top, which is lower pressure that the bottom. Thus a vacuum pulls the air foil up.

Answer 7

gyroscopic effect.