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This post is about an experiment of mine , which was for me, remarkably interesting!

Why do I post it here?

I'm interested in knowing the physics behind this.

MATERIALS USED

holding the pen A light weight sketchpen.

THE EXPERIMENT

I took a sketch pen, and held it by its tail. After some practice, I could manage to fling the pen up in the air while getting it to spin about the axis passing through its length.

So I had a spinning pen , going up in the air and moving through unusual paths.

I repeated the process many times to arrive at a conclusion. It seemed as if a force acted on the pen, perpendicular to its length, on the side which has a spin complementary to the direction of air flow.

So if I flung the pen up vertically, it would first accelerate towards one direction during the ascend, and then, accelerate in the opposite direction during the descend.

Now for the BEST PART:

I threw the pen, with its length parallel to the ground horizontally with spin in an anticlockwise direction w.r.t the ground. It hit the ground earlier than expected.

Next , tried the same with clockwise spin. As I expected, the pen stayed in the air for a longer than usual time.

I gradually increased the the spin to such an extent, that the pen appeared to float in the air ! Diagrammatic representation It had apparently no vertical acceleration! It just moved horizontally with a constant velocity, till it hit the side walls and landed.

It seemed magical to my family and friends !

Now I wonder what made the pen fly.

Whatever it is, I know that it depends on the spin velocity, spin direction and the air flow.

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1 Answer 1

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This is a well known Magnus Effect effect described by NASA here : Lift of rotating Cylinder. Hope this helps :)

enter image description here

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  • $\begingroup$ So, can't we make lightweight flying vehicles with rapidly spinning cylinders instead of tyres? $\endgroup$
    – AlphaLife
    Commented Sep 23, 2017 at 12:32
  • $\begingroup$ Yes, a chopper would be pretty straightforward, a plane a bit trickier. Neither would be more efficient than existing designs of course, but a small chopper with rotating cylinders would be a fun toy :) A two-propeller helicopter also should work, as there is no principle difference between propellers and rotating cylinders. Trickier with a plane as the cylinders would replace the wings and the angular momentum would need to be compensated from nosing the plane down. Plus something would need to propell the plane forward. It would be hard for it to take off. $\endgroup$
    – safesphere
    Commented Sep 23, 2017 at 18:05
  • $\begingroup$ Interesting. Infact, I found that there really does exist the magnus effect planes. See google.co.in/url?sa=t&source=web&rct=j&url=https://… $\endgroup$
    – AlphaLife
    Commented Sep 24, 2017 at 7:09
  • $\begingroup$ Like I expected, hard to take off. The guy had to throw it every time. A helicopter would be much cooler. Make one :) $\endgroup$
    – safesphere
    Commented Sep 24, 2017 at 7:58
  • $\begingroup$ I would like to, once I'm out of school!! $\endgroup$
    – AlphaLife
    Commented Sep 24, 2017 at 8:00

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