Not sure if this is the right place to ask, but it is for a physics experiment.

I'm trying to find out how the internal diameter of a copper pipe affects the time it takes for a magnet to drop through. Dropping the magnet in the centre would allow me to ensure consistency for each drop.

  • $\begingroup$ How tight of a fit is it? $\endgroup$
    – Eric S
    May 20, 2021 at 13:37
  • $\begingroup$ Use a precise funnel $\endgroup$
    – jko
    May 20, 2021 at 13:51
  • 2
    $\begingroup$ Drop the magnet down a plastic tube held in the centre of the copper pipe. $\endgroup$
    – Transistor
    May 20, 2021 at 13:53
  • 4
    $\begingroup$ I had a university research job where we did these drop-tower like experiments that required 2mm ball bearings to collide in mid air and intersect at a repeatable height and with repeatable horizontal offset (controlling contact angle)... We held them from above with a vacuum suction (stiff metal hole), and used a solenoid valve to shut off the vacuum. Got good timing control and very clean release that way. $\endgroup$
    – Pete W
    May 20, 2021 at 14:46
  • $\begingroup$ @EricS I'm using a square magnet, cus I couldn't find a round one. Its dimensions are 1.2cm x 1cm x 1cm. The diameters I'm using are 2, 3, 4, 5, 6 cm $\endgroup$
    – prata
    May 21, 2021 at 2:57

1 Answer 1


Illustration following up from the comments

We used vacuum to hold the ball bearing being dropped, from above. The ball was hand placed up against the output port of a manifold. Around it was open air. The port holding the ball connected to COMMON port of a 3/2 solenoid valve. NC to vacuum regulator, NO vent to atmosphere. When valve vented the output, part went into free fall.

There wasn't much to it, really, although we had the benefit of symmetry, and the sphere-circle contact made great repeatability in horizontal position.


  • $\begingroup$ Align with a laser pistol site. Match parallax to target. $\endgroup$
    – Phil Sweet
    May 22, 2021 at 21:07

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