Comments on: Fun for a girl and a boy http://blog.richmond.edu/physicsbunn/2012/06/25/fun-for-a-girl-and-a-boy/ Department of Physics Fri, 17 May 2013 11:27:54 +0000 hourly 1 http://wordpress.org/?v= By: Cash For Cars NJ http://blog.richmond.edu/physicsbunn/2012/06/25/fun-for-a-girl-and-a-boy/comment-page-1/#comment-219123 Cash For Cars NJ Sun, 05 Aug 2012 20:59:28 +0000 http://blog.richmond.edu/physicsbunn/?p=485#comment-219123 Im going to check out the movie now! Interesting topic Ted Im going to check out the movie now! Interesting topic Ted

]]> By: Ted Bunn http://blog.richmond.edu/physicsbunn/2012/06/25/fun-for-a-girl-and-a-boy/comment-page-1/#comment-218362 Ted Bunn Sun, 15 Jul 2012 18:41:34 +0000 http://blog.richmond.edu/physicsbunn/?p=485#comment-218362 Sorry about that! This should be a link to the right movie: http://youtu.be/uiyMuHuCFo4 Sorry about that! This should be a link to the right movie: http://youtu.be/uiyMuHuCFo4

]]> By: Tam software http://blog.richmond.edu/physicsbunn/2012/06/25/fun-for-a-girl-and-a-boy/comment-page-1/#comment-218328 Tam software Sat, 14 Jul 2012 22:31:35 +0000 http://blog.richmond.edu/physicsbunn/?p=485#comment-218328 Great post, but from here the movie isn't about the slinky anymore but particles ... Great post, but from here the movie isn’t about the slinky anymore but particles …

]]> By: Ted Bunn http://blog.richmond.edu/physicsbunn/2012/06/25/fun-for-a-girl-and-a-boy/comment-page-1/#comment-216908 Ted Bunn Tue, 26 Jun 2012 18:26:31 +0000 http://blog.richmond.edu/physicsbunn/?p=485#comment-216908 In a followup post, I give an analysis based on Allen's idea but incorporating what I think is the correct density profile: http://blog.richmond.edu/physicsbunn/2012/06/26/more-on-the-slinky/ In a followup post, I give an analysis based on Allen’s idea but incorporating what I think is the correct density profile: http://blog.richmond.edu/physicsbunn/2012/06/26/more-on-the-slinky/

]]> By: Ted Bunn http://blog.richmond.edu/physicsbunn/2012/06/25/fun-for-a-girl-and-a-boy/comment-page-1/#comment-216900 Ted Bunn Tue, 26 Jun 2012 15:00:51 +0000 http://blog.richmond.edu/physicsbunn/?p=485#comment-216900 I don't think your analysis is quite right, although it's got some of the main features of the motion qualitatively right. The problem is that your center of mass calculation assumes that the linear mass density along the stretched slinky is uniform, but it's not. The slinky is much more stretched at the top (so has a lower mass per unit length) than at the bottom. This is, I think, a pretty big effect. I don’t think your analysis is quite right, although it’s got some of the main features of the motion qualitatively right. The problem is that your center of mass calculation assumes that the linear mass density along the stretched slinky is uniform, but it’s not. The slinky is much more stretched at the top (so has a lower mass per unit length) than at the bottom. This is, I think, a pretty big effect.

]]> By: Allen Downey http://blog.richmond.edu/physicsbunn/2012/06/25/fun-for-a-girl-and-a-boy/comment-page-1/#comment-216893 Allen Downey Mon, 25 Jun 2012 22:58:21 +0000 http://blog.richmond.edu/physicsbunn/?p=485#comment-216893 I think it is more interesting than you are giving it credit for. You explain qualitatively why there is a delay, but the interesting part is that (to my eye at least) the top of the slinky accelerates quickly and then moves at constant speed. I think I have an explanation: If I am right, then the slinky basically pancakes from top to bottom. So imagine that initially the top is at h=1 and the bottom at h=0. At some point, the top x units have collapsed, but the bottom 1-x are still standing. So the center of mass is x(1-x) + (1-x)(1-x)/2. But since the slinky is in freefall, the center of mass, as a function of time, is 1/2 - 1/2 g t^2. Set them equal, solve and get x = sqrt(g) t, valid until t = 1 / sqrt(g) and x=1. So I think that's why the top falls at constant speed. What do you think? I think it is more interesting than you are giving it credit for. You explain qualitatively why there is a delay, but the interesting part is that (to my eye at least) the top of the slinky accelerates quickly and then moves at constant speed. I think I have an explanation:

If I am right, then the slinky basically pancakes from top to bottom. So imagine that initially the top is at h=1 and the bottom at h=0. At some point, the top x units have collapsed, but the bottom 1-x are still standing. So the center of mass is x(1-x) + (1-x)(1-x)/2. But since the slinky is in freefall, the center of mass, as a function of time, is 1/2 – 1/2 g t^2.

Set them equal, solve and get x = sqrt(g) t, valid until t = 1 / sqrt(g) and x=1. So I think that’s why the top falls at constant speed.

What do you think?

]]> By: Raymond http://blog.richmond.edu/physicsbunn/2012/06/25/fun-for-a-girl-and-a-boy/comment-page-1/#comment-216892 Raymond Mon, 25 Jun 2012 22:37:57 +0000 http://blog.richmond.edu/physicsbunn/?p=485#comment-216892 This implies that a slinky dropped on the moon may exhibit a different type of behavior. This clearly requires additional experimental verification. This implies that a slinky dropped on the moon may exhibit a different type of behavior. This clearly requires additional experimental verification.

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