Question

http://www.youtube.com/watch?v=raurl4s0pjU

How does Walter Lewin do this? Can I do it on pencil and paper?

Answer 1

I can replicate it with a blackboard and chalk, although he's clearly more practiced at getting uniform dots/dashes than I am.

Having the motion of the chalk in a vertical plane is important; I can't make this work a horizontal plane with pencil and paper, as I can't get the bounce in the writing implement against the gravitational force.

Answer 2

He often jokes about it on facebook, he is the awesomest!

Answer 3

You can't do it on paper because graphite (essentially a lubricant) != chalk.

My theory is that he does it by pressing a little harder into the chalkboard with a constant force at an angle > 90 degrees with respect to the direction of the line he is drawing. This should cause the chalk to skip along the board. Again, it's just my theory...I don't have a chalk board to try it on :)

What's more interesting is how consistent his lines are...a skill which I'm sure took a while to perfect. Still, it's a funny video to watch.

Answer 4

Shall i mail him and request him to come here to answer this? Will he come?

Answer 5

What's even funnier is the thought that someone took the time to make the video :)

Answer 6

@stormfire1 , the lubricant/high friction comparison between the chalk and the graphite is really key. Nicely observed.

Honestly guys, if you want to understand it, try it! Experiment! That's what any good scientist would do.

Answer 7

it does depend a little on friction on the surface but mostly depends on using a sharp chalk tip(or some pointed portion in the surface) and there should be minimal point of contact between the board and the chalk
when u do it fast u leave dotted lines than when u press fully against the board

it is really fun doing that and professor makes use of these dotted lines to explain everything more clearly!
love his videos!

Answer 8

@stormfire1 Here's an even more amusing (and time consuming to make) dubstep version of the same video. http://www.youtube.com/watch?v=E-dUx9fgbW0

Answer 9

hilarious

Answer 10

Love his lectures. I just wish they'd recorded them in HD. Oh well.

Answer 11

In regards to doing this with a pencil. I've accidentally done it while using an old fashioned wooden pencil with cheaply made "lead" at the right angle and light pressure. Good luck replicating it with a Dixon Ticonderoga.

Answer 12

I agree. I wouldn't have passed Magnetism and Light without his lectures. His demonstrations, german accent, and sense of humor keep you glued.

Answer 13

Dutch, not German. I think he would insist I tell you that.