Hi guys,

Please could you help with with a puzzling question for a non physics person. I am sure it has a simple answer.

Today at the park, my kids and I discovered a strange physical phenomenon while playing with a tennis ball and a large stainless steel tube (the kind you crawl through).

Whizzing the ball around the inside of the tube at 90 degrees to the tube long axis, the ball goes round and round the inside circumference until it runs out of steam. This continues at 90 degrees, staying on the orginal plane. Good.

Firing the ball into the tube, while giving it some rotation too I expected it to spiral all the way to the other end. Along plus Round equals Corkscrew?

No.

If you fire the ball in at an angle, not only does it travel around the circumference but it tries to return to the thrower at a similar angle. This means that after a few rotations, the ball ends up travelling around the inside of the tube at 90 degrees to the long axis again.

It seems impossible to get the ball to corkscrew to the other end AND get a number of rotations around the tube - the ball always returns to the 90 angle of travel.

This behaviour must have a name. What can I look for to find out more?

Cheers

Rob

and two small children

Please could you help with with a puzzling question for a non physics person. I am sure it has a simple answer.

Today at the park, my kids and I discovered a strange physical phenomenon while playing with a tennis ball and a large stainless steel tube (the kind you crawl through).

Whizzing the ball around the inside of the tube at 90 degrees to the tube long axis, the ball goes round and round the inside circumference until it runs out of steam. This continues at 90 degrees, staying on the orginal plane. Good.

Firing the ball into the tube, while giving it some rotation too I expected it to spiral all the way to the other end. Along plus Round equals Corkscrew?

No.

If you fire the ball in at an angle, not only does it travel around the circumference but it tries to return to the thrower at a similar angle. This means that after a few rotations, the ball ends up travelling around the inside of the tube at 90 degrees to the long axis again.

It seems impossible to get the ball to corkscrew to the other end AND get a number of rotations around the tube - the ball always returns to the 90 angle of travel.

This behaviour must have a name. What can I look for to find out more?

Cheers

Rob

and two small children

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