# Uniform frisbee motion

1. Apr 16, 2005

### T@P

Ive been wondering how frisbee's move around since like 3 hours ago, and heres my take:

frisbees move specially only becuase of air, i.e. they dont fly as well in a vacuum.

but as to how they move, this is what i think. the firsbee spins, so everywhere near the frisbee there is lower air pressure (one of bernoulis laws i think. or something like that). however there is lower pressure all around it so all the forces sort of negate each other and it just floats with little air resistance because of that. (therefore the initial push pushes it better all the way throughout). the fact that its curved i believe will trap some air there, (the lower pressure will keep the air coming there, essentially a pillow of air). thats why they float...

is any of this right? or is it all some drivel i concocted?

thanks for the help

oh and theres something similar in it to a gyroscope - thats why they dont tilt as much.

??

2. Apr 17, 2005

### Andrew Mason

They don't fly at all in a vacuum. They would drop with acceleration g.

The frisbee spin makes it stable. But its shape makes it fly. It has the shape of an airfoil so there is lower pressure on top than below. Just how that occurs is not simple and is subject of much debate. It is not a simple Bernoulli principle.
and this one

AM

3. Apr 17, 2005

### T@P

so theres no nice formula, like input the speed it rotates at, and the initial force on it and you can calculate where it went?

4. Apr 17, 2005

### Hurkyl

Staff Emeritus
I doubt it, especially with all the tricks one can do with frisbees -- for instance, you can throw it forward and have it land behind you, or throw it at a downward angle, and it will lift itself back up!

5. Apr 17, 2005

### Ryan H

I'm pretty sure it's mainly that the spinning causes lower pressure. Because, if you throw a frisbee upside down, it hits the ground very quickly.

6. Apr 17, 2005

### T@P

i tried it, and Ryan H is exactly right.

still, too bad. you can start a whole new area of physics, Uniform Frisbee Motion.

you can even expand it into hitting falling monkeys with frisbees, etc etc

lol

7. Apr 17, 2005

### Andrew Mason

Your logic is not very clear. Why do you think B (if you throw a frisbee upside down, it hits the ground very quickly) implies A (the spinning causes lower pressure)?

AM

8. Apr 17, 2005

### Hurkyl

Staff Emeritus
In my experience, frisbees thrown upside-down don't hit the ground "very quickly".

9. Apr 17, 2005

### OlderDan

"Lift" depends on the shape of an airfoil, but it also depends on the angle of attack. The only fair comparison would be to throw two frisbies perfectly horizontally in still air, one upright and one upside down. An upside down frisbie thrown at an upward angle would get some lift from the attack angle.

10. Apr 18, 2005

### T@P

It may be explained because i try to throw my frisbees horizontally... I never mastered the 'bounce' trick, where it goes down and then back up without hitting t he ground.