MIT Physics Demo -- Strobe of a Falling Ball

A ball is dropped in front of a meter stick and lit by a strobe light. A long exposure photograph captures the position of the ball at each evenly spaced flash of light. The acceleration of the ball can then be measured from the photo.

Note that the frame rate of the video capture (30fps) is quite close to the strobe rate (15Hz). This is why the strobe flashes in the slow motion video don't appear to be exactly evenly timed.

See the final image on Flickr - http://www.flickr.com/photos/physicsdemos/3174207211

See the original video on MIT TechTV - http://techtv.mit.edu/videos/831-strobe-of-a-falling-ball

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[salman06p0020]

So this proves that the ball is accelerating. Kids can easily watch and learn from this video. Pretty good. Keep it up.

[RababaInc]

Sometimes I just want to fucking SLAP my dick as hard as possible on my desk!

[lovelplants]

very good demo,,,

[LlamaLuver86]

I'm doing a science fair project like this. Can you tell me how far apart the flashes are (in seconds)?

[tty2020]

using very light balls will reach a terminal velocity, and this can be seen under the strobe light (reaching same distance intervals)

[SomeWeirdFreak]

@jawnlooi It actually varies as the 9.81 is based on a theoretical average of Earth's radius. You're presuming the reference point to be about 6.37E6 from Earth's center. In terms of most applications though, you are correct that it is about +-9.81m/s^2 for acceleration and deceleration respectively.

[danielinsporto]

not sure i understand the point of the strobe here

[viptutorialscom]

@thewolf2114 NOPE! :) In this experiment AIR RESISTANCE IS PRESENT, which can be tought as force pushing the ball in upwards direction (gravity = force pulling the ball downwards). Therefore, if you were to measure the accelation due to gravity using example in the video you would get a WRONG result (accelaration would be LESS then -9.81m/s^2, since force of friction extends the time the ball takes to reach the ground). Remeber a=change in velocity/change in time (t increases, a decreases).

[viptutorialscom]

@aprenderpontofinal Hehe, mass of the ball is irrelevant :)  Accelaration = change in velocity / change in time.

1g or 1kg ball will be accelarated by a=-9.81m/s^2 since there are no other forces acting on it (we have to presume there is no air resistance).

[alcosher]

@aprenderpontofinal they are quarter meters so he is only 1.25 meters