# Newton's Third Law with Skimboarding?

1. Nov 11, 2008

### gibxam

Hello PFers,

I've been reading these forums for a little while, and now that I have my own question I thought I would register to the site :).

My question is about pumping and Skimboarding. I understand that many of you (if not all) have no idea what skimboarding and pumping even is. Please watch http://www.youtube.com/watch?v=D5osvrbTyF4" and skip to 4:18 for a perfect example of what I am talking about.
NOTE: I have posted the video below but if you go to the link you can use the option to watch in high quality which makes the video much more clear.

To clear up what I mean by pumping, and what you should be seeing in the video; it is when you stomp your front foot up and down on the top of the board, this makes you travel faster and farther across the water before you sink.

I have been curious for a long time why pumping has this effect and recently while doing some physics homework reading I think I may have found the answer! I was doing reading on Newton's Third Law about equal and opposite reaction for every action. I came to the conclusion that because the skimboarder is pushing down (action) on the water the water is pushing back (reaction) with equal and opposite force thus keeping the board floating/above the water for longer. This would be a similar effect to a bird flying. Is this correct? If not what is the reason for pumping helping in skimboarding? Also if there is another part of this I am missing please elaborate.

Thank you for your time, I am looking forward to hearing about the answer to this question as well as becoming part of the forums :).

-Max

Last edited by a moderator: May 3, 2017
2. Nov 12, 2008

### Danger

Welcome to PF, Gibxam.
In this case, I'd be more inclined to think of the 'pumping' action as actually being a pumping action. It would appear that you are altering the waveform of the water beneath the board, and forcing it rearward in a jet-like manner.

3. Nov 12, 2008

### gibxam

Hey Danger,
Thanks for the response but I'm still a little bit confused. How does altering the waveform force it rearward in a jet-like manner? Does this mean the the reason pumping works does not have to do with Newton's Third Law? Also could you elaborate on what you mean by a jet-like manner? Do you mean that because board is pushing the water backwards the water molecules are pushing the board forward? In this case it would be NTL.

4. Nov 12, 2008

### Danger

That's pretty much what I'm thinking. It looks to me as if the board is... not sure how to say it... redistributing the water from its original waveform to one with a much higher frequency and channeling it rearward.
This really is not something that I know anything about, though, so you should wait for someone else to weigh in.

5. Nov 12, 2008

### gibxam

Alright thanks for the input anyways Danger :)

6. Nov 12, 2008

### Danger

No worries, mate. There are a few dudes around here with awesome knowledge of fluid dynamics. They can tune you in to what's really going on, but sometimes it takes a couple of days for one to chirp up.

7. Nov 14, 2008

### gibxam

Comon guys 91 views no answers? I'm going to do some more research on fluid dynamics and post about it but I'd really like to here at least where to start I did some reading and its difficult to know where exactly I should be looking.

8. Nov 17, 2008

### Danger

If nobody else has answered after viewing this, it might be that even the experts don't know what's going on. In that case, you can assume that they're researching the matter in order to properly inform you.

9. Nov 17, 2008

### gibxam

My apologies for coming off as rude Danger I will be more patient :)

10. Nov 17, 2008

### Danger

Oh, I wasn't interpreting your comment as rude. I know how frustrating it can be to wait for help when it appears on the surface that you are being ignored.
You have to be around PF quite a while before you 'tune in' to how the various individuals approach things. I'm one of the very few 'old-timers' who will just lay an idea on you that might or might not be correct. The professionals make sure of their facts first.

11. Dec 10, 2008

### gibxam

I'm trying to bring this thread back to life as I am still curious about the answer.

12. Jun 30, 2009

### postdiluvium

This answer may be a little late, but I found this thread searching skimboard sites on Google. It actually is not making the person faster. Watch and you will see that the person is slowing down. Skimboarding is basically hydroplaning. Skimboards are smaller than surfboards, so they do not have the surface area to stay afloat like surfboards. So what is happening there is the guy is slowing down, which will eventually lead him to sinking into the water as the forward force is decreasing enough to allow gravity to take effect more.

To delay the inevitable, he is actually rocking the board back and forth. Its called "pumping", but its actually rocking. Skimboards are made with a slight curvature towards the nose of the board. So rocking the board back and forth is just a way to reestablish the board's rest on top of the water by creating a little burst of forward momentum that swings the board up and out of the water to land on the water. Doing it rapidly, as seen in the video, is just the board sinking into the water and hopping back to the surface over and over again.

13. Jun 30, 2009

### postdiluvium

If you catch the parts of the video where they are actually skimming on the waves and the camera is scrolling across the wave giving you a side view of the skimmer, you will notice they are also "pumping" their boards to stay afloat.