In: Physics
Why does a frisbee behave differently when thrown upside down?
Explanation :
There are two factors which influence the flight of a Frisbee, gravity and air. Gravity acts on all objects the same way, accelerating their mass towards the center of the Earth at 10 meters/second. Once in the air, lift and angular momentum act on the Frisbee giving it a ballet-type performance. Lift is generated by the Frisbee's shaped surfaces as it passes through the air. Maintaining a positive angle of attack, the air moving over the top of the Frisbee flows faster than the air moving underneath it.
Under the Bernoulli Principle, there is then a lower air
pressure on top of the Frisbee than beneath it. The difference in
pressure causes the Frisbee to rise or lift. This is the same
principle that allows planes to take off, fly and land. Another
significant factor in the Frisbee's lift is Newton's Third Law
which states that for every action there is an equal and opposite
reaction. The Frisbee forces air down (action) and the air forces
the Frisbee upward (reaction). The air is deflected downward by the
Frisbee's tilt, or angle of attack.
Spinning the Frisbee when it is thrown, or giving it angular
momentum (gyroscopic inertia), provides it with stability. Angular
momentum is a property of any spinning mass. Throwing a Frisbee
without any spin allows it to tumble to the ground. The momentum of
the spin also gives it orientational stability, allowing the
Frisbee to receive a steady lift from the air as it passes through
it. The faster the Frisbee spins, the greater its stability.
If your Frisbee was thrown upside down, the difference in speed of air between the top and bottom would be revered and instead of lift, the Frisbee would get pushed into the ground. As for the spin: if there wasn't any spin, the Frisbee would be so unstable that it would just crash and fail to cut through the air.