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Help me with my physics paper: PLEASE READ!

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wizpig
Posts: 67 - Karma: 10
Here is the assignment:

I. Physics of Sports

This project focuses on how things in sports/movement work and your understanding of the physics involved based only our current knowledge of physics augmented by the research you do over the summer. You may pick your favorite sport or another approved activity such as dance for example.

Consider this project and instructional document that could be used to improve a player's performance or improve equipment design. You could play the role of the coach (dance instructor) or the design engineer of a major sports equipment supplier. The following elements must be included in your proposal for your players or corporation.

1. Choose at least 2 aspects of the movement to breakdown and explain, equations may be useful here (numerical support is not necessary but if it helps in your discussion, use it)

2. Explain the physics of the movement using correct terminology and your own words and understanding of the concepts. Plagiarism will not be tolerated and will result in no credit for this assignment.

3. Diagrams must be included along with your text, they can be hand drawn, computer generated or cut and pasted from the internet as long as the source is cited.

4. Cite your sources in proper MLA or aPA format. Wikipedia cannot be used as a source.

I've decided I want to try and do the project on skiing, because it would be unique and enjoyable for me. Keep in mind, I only have basic physics knowledge because I've only taken a semesters worth, and i'll be going into junior year of high school for AP physics. I'm posting this because I would like you guys to share some ideas you have for me (please give reasonable answers, and only if you have the correct knowledge of the subject). If i'm a bit unclear in this post, please follow up with me on the issue and I will clarify.

Thanks!


Aug 10 2010 12:19PM
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ChrisSkisChronic
Posts: 1128 - Karma: 230
Do something about acceleration and the pull gravity. Have an example like "a skier drops a 13m cliff with an initial velocity of 7m/s, determine his final speed using the gravitational constant G=9.8 m/s/s" Solve your problem, use diagrams and show all your work/formulas 
Aug 10 2010 12:43PM
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loganimlach
Posts: 5132 - Karma: 14,061
one way to get around the whole "designing equipment" part would be talking about how to develop faster skis by finding a material that reduces the static and kinetic coefficients of friction between the bases and the snow. lord knows that ski companies have damn near as good as it gets in that dept., and that wax is truly all that matters, but its a start. plus the calc's on that will be super easy to illustrate.
Aug 10 2010 12:51PM
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airic
Posts: 720 - Karma: 16
Here are some ideas:

(1) How the pressure exerted by the skis causes the freezing point of the snow underneath to be lowered, thereby causing some of the snow to melt, creating a kind of lubricant that helps the skis to slide more smoothly (you can easily find info on the physics of water that explains why it expands upon freezing)

(2) What angle to have a jump take off with respect to the ground in order to maximize the total time in the air when the jump is on a steep slope of some fixed angle.








Aug 10 2010 1:15PM
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loganimlach
Posts: 5132 - Karma: 14,061
(1) it takes a lot more that pressure impulse to melt the snow beneath your skis, especially when the surrounding temp is fighting that effect.

(2) maximization of your time in the air is a 45 degree angle, which is most definitely not optimum for skiing because of the compression involved.
Aug 10 2010 1:22PM
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Mike.Records
Posts: 1311 - Karma: 756
Actually I'm pretty sure that 45 degrees maximizes your distance traveled on flat ground. Time in the air would be maximized on a flat surface by going straight up(quarter pipe), and is dependent on the slope for going of a jump down a hill.


Some other ideas:

1) Terminal Velocity: How fast can you go on a 30 degree slope? 40? Should be pretty easy by assuming that the human body is a square or rectangle then you should be able to pull a drag coefficient out of your physics book for that shape. You could either add in the force of friction between your skis and the snow or ignore it.

2) Height jumped vs angle of jump at a certain speed. How high do you go off a quarter pipe vs a park jump at the same speed.?

3) A variation on ChrisSkisChronic's idea: You go off a cliff with a given horizontal velocity. How far down the slope/away from the cliff do you land given a certain landing slope.

4) Rotational Motion: You could do something with a skier doing a backflip at a certain rotational velocity and how much they need to tuck to speed up their flip by a certain rate. Assume the skier is a column/rectangle shape and the moment of inertia calc won't be too hard.

Don't really know what kinda physics knowledge you have. Let me know if these are too boring and I can come up with some harder ones.




Aug 10 2010 2:47PM
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wizpig
Posts: 67 - Karma: 10
My knowledge is VERY basic. We didn't even cover terminal velocity or rotational motion last year. I appreciate all this work you guys are putting into this! Keep the ideas coming, but remember, BASIC stuff

thanks
Aug 10 2010 2:58PM
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CAPSLOCK*
Posts: 345 - Karma: 19

Make a chart to fix the speedcheck problem. Consider the angle of the booter, the flat lenght and possibly the height of the landing (step-down vs step-up vs ...). Example : For a 30 degree booter, travelling over a 60 foot flat and landing 2 meters below the kicker you need to be travelling at X km/h when leaving the edge of the booter. To make things more simple you'll need at least 2 hypothesis : zero wind and a standard weight for the skier (that's up to you).

I bet dumont would have liked one of these a few years back.

Aug 10 2010 3:25PM
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.peter
Posts: 1222 - Karma: 63
explain why Tanner Hall failed to make Chad's gap... (seriously) factor possible wind resistance, speed and deceleration and distance.
Aug 10 2010 3:42PM
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airic
Posts: 720 - Karma: 16

The pressure effect I described is probably significant when you are on an edge, since the pressure exerted becomes much higher (for ice skates it is major). I have no idea how important it is when you have your skis flat (the invesitgation would be part of the project I guess).


As someone above said, the 45 degree angle is to maximize HORIZONTAL distance, when going over flat, level ground, and ignoring air resistance.

My second idea for the project actually has a really simple result (the math may be wrong; i did it quickly):

Ignoring air resistance, for a jump of angle theta going off the top of a slope of angle phi, you get maximum air time when

theta = 90 degrees - phi

... so in other words, its just like finding the other angle of a right-angle triangle !

Aug 10 2010 5:20PM
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LC.
Posts: 5952 - Karma: 2,423
Do it all about ski technology. Width, rocker, soft/stiff and so on. Relate it to flotation, stability and ease of use. This is all physics and your teacher doesn't need to know that this sort of technology exists already.
Aug 10 2010 5:38PM
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Uncle.Badness
Posts: 2545 - Karma: 55
Do the angle of the takeoff of a jump in correlation with how big the jumps is to the knoll and how fast you have to be going to land in the sweet spot.
Aug 10 2010 5:40PM
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loganimlach
Posts: 5132 - Karma: 14,061
I agree that a 45 is for maximum horizontal distance, that was my bad. I just think that doing calc's for launch angles of jumps may violate the reality of compression in the transition when you over simplify them, ending up with 60 degree launch angles and such. plus, if he did want to get real, the compression calc's may be a little over the OP's basic physics knowledge (no offense meant whatsoever OP), because there you're getting into impulse dynamics.
Aug 10 2010 5:55PM
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wizpig
Posts: 67 - Karma: 10
bump! still need more help, thanks!
Aug 12 2010 11:07AM
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chardi
Posts: 5040 - Karma: 59
the one thing i always wanted to do was to make a forumula for the friction of different surfaces we ski on. snow, turf, metal, ect. it was an idea for summer setups, or any setup, to gauge speed. the idea was to calculate the coefficient of friction for all surfaces, and make a single formula (with spots to plug in height, surfaces, ect) and get a single simple answer as to how much speed you will have, how much you will need, and how much you will have leaving the end of the feature. all you would need would be a decently sized lenght of each surface, and a scale with a rope to measure the kinetic and static friction. then it would just be simple math. but i am much to lazy to do any of this. it would make a great project though.
Aug 12 2010 11:23AM
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SketchySwiss
Posts: 393 - Karma: 43
I had a problem this year that was :

"How deep must be the snow coat so a skier jumping-falling from X [m] don't break his tissues (explose or break his leg if you prefer)." (given the skis surface, height of the jump, human tissues resistance constants etc...). It was actually harder than it looks.

You could imagine some new material (FOR skis or boots) that would lower the force transmitted to the skier and thus protect him. Some kind of shock abosrber like in a car but on on skis.


Aug 12 2010 11:32AM
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loganimlach
Posts: 5132 - Karma: 14,061
this would be legit, just have a bunch of trial runs and back calc for your coefficient for friction, then do a comparative analysis on which surfaces are the best for different configurations. i think that would be a winner for you good sir! plus teachers always love to see that you've actually run experiments.
Aug 12 2010 12:16PM
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wizpig
Posts: 67 - Karma: 10
knowledge bump!
Aug 13 2010 9:21AM
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I_Am_Mod
Posts: 13214 - Karma: 3,753
i'm quite sure 45° takeoff is only ideal in theory
(if your aim is to bridge the longest horizontal distance....)

Considering airfriction/drag an you'll get a lower angle, 40° or maybe even 30° ....
Aug 13 2010 10:59AM
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wizpig
Posts: 67 - Karma: 10
bumpppp. for one aspect of the project, i want to break down the physics of a regular ski jump, so i figure i'd want to use the classic tanner hall chads gap example to makes things fun. because my physics knowledge is so basic, i sorta need some help creating and solving a physics model

Lets create an example, and hopefully you guys can help me out ( not real chads gap specs)

Tanner takes off at a 30 degree angle and begins to travel over the gap. The landing is 10 meters below the takeoff booter, and the gap is 80 meters wide. Find Tanner's minimum initial velocity to clear the gap.

I believe that is enough information to solve the problem. It's super basic physics, so please don't try going into great depth because i probably won't understand it. i'd appreciate it if you just broke down the problem and guided me to solving it correctly.

thanks a bunch


Aug 16 2010 1:37PM
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Tripplesixty
Posts: 835 - Karma: 148
http://www.sendspace.com/file/r1ybvx

Check the link its PDF with some instructions.. You'll need some basic algebra skills to solve this but the method should be self explanatory... basically once you get it to the final equation you can plug in different initial velocities and see what value you get for the distance of the gap.

Good luck...

Aug 16 2010 2:21PM
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Mike.Records
Posts: 1311 - Karma: 756
I know that you are probably just providing an example, so sorry if this is obvious, but I think that 80m is unrealistically large for chads gap. Probably more like 30m would be accurate. You would need to go soooo fast to clear a 80m jump! :) Also, considering that the speedgun that day I believe picked up a max speed of Tanner of 55 mph you could compare your predicted speed and the actual speed and discuss why there are differences like wind resistance etc.
Aug 16 2010 3:19PM
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AbeFroman
Posts: 1268 - Karma: -4
i had to do basically the same project we could do any sort of thing so i made a video it was pretty easy cuz a had a lot of footage from the season. if you want i could post it but its kinda basic i did it super quick
Aug 16 2010 3:48PM
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wizpig
Posts: 67 - Karma: 10
bump. need more ideas
Aug 17 2010 5:03PM
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Rob.
Posts: 189 - Karma: 16
Not exactly sure how much you know at this point, but I'm assuming you've touched on linear momentum (and impulse?) at least.

You could say a skier is going down a slope with a given slope angle and velocity down the slope, skis over a kicker for a certain time duration, and leaves the kicker travelling at a given angle (the end angle of the kicker) with a certain velocity. If you neglect friction/air resistance, find the average force exerted on the skier by the kicker. (Assume the skier is a point mass).

For many of the questions relating to a skier's motion during a jump, look up projectile motion (http://en.wikipedia.org/wiki/Projectile_motion).

Always neglect air friction for your purposes. You do not want to go down this path.

As for experimentally finding the coefficients of static/kinetic drag, there are many variables involved. You will have to simplify this down, and most likely keep it only theoretical.

If you do want to consider air resistance, you could simplify it in your problem to assume that it is only a function of the front-view projection area of the skier (approx. true for a skier's body). You could then branch this off into one of two questions. One: why does curling/crouching/going into a tucked position increase the maximum speed of a skier. Two: why are heavier skiers able to attain a higher maximum speed than a lighter skiers, all other factors considered equal (including the above-mentioned area).

Too bad you don't know any angular momentum. That takes spins/flips out of the question.
Aug 17 2010 7:30PM
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Yung_Gnarley
Posts: 9092 - Karma: 3,022
...probably the smartest superunkown winner ever.
Aug 17 2010 7:39PM
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FerrisBueller
Posts: 8280 - Karma: 5,173
my threads for physics class later this year.
Aug 17 2010 9:51PM
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tride
Posts: 1038 - Karma: 26
Actually..... lots of the time, the ski is melting the snow, until we get into really cold snow (15F/-10C and lower).

At temperatures above about 15F the skis are gliding on a thin film of water. This water is created by the friction of the ski melting the snow. This is wet friction. The different waxes try to manage the production of water to produce optimum glide. Too much water and you get suction and the ski slows down. Too little water (dry friction) and the ski slows down. Dry friction conditions are generally slower than wet friction conditions. At temperatures below 15F you can’t make enough friction to create any water. Under these conditions the smoother and harder the ski base the better the glide. That’s why we put on hard wax, have minimal structure and polish the bases when it’s very cold. So the simple rule is hard waxes for cold temps, soft waxes for warm temps. The extra water problems caused by warm or wet snow are handled by using fluoro waxes which repel water, similar to the way water beads up on a waxed car. By repelling water the suction is reduced. Ski structure is more important than wax when dealing with wet snow.


Aug 18 2010 2:40AM
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wizpig
Posts: 67 - Karma: 10
hahah unfortunately my knowledge is even more basic than that. i wouldn't be able to do that problem you set up right there..
Aug 18 2010 1:51PM
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Tripplesixty
Posts: 835 - Karma: 148
It wouldn't be that hard to do a double integral over a function of air resistance vs speed of a cylinder traveling through air... noway unless you have a computer sublimation to get any more complicated than that... however this mostly neglectable.. you could just as easily subtract 10% of the theoretical distance as a safety factor.
Aug 18 2010 2:00PM
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wizpig
Posts: 67 - Karma: 10
bump.. can anyone help me with the problem posted above? i'm still confused on projectile motion with an angle
Aug 20 2010 11:03AM
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Tripplesixty
Posts: 835 - Karma: 148
http://fs08n5.sendspace.com/dl/5fabc91c0923486d7675506cca5e11e1/4c6eb2f57e672180/r1ybvx/ski.pdf
Aug 20 2010 12:53PM
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creamypies
Posts: 143 - Karma: 11
yeah and then you can put once the skier lands he exerts X amount of pressure on the snow due to some fatty rocker skis or something
Aug 20 2010 12:58PM
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loganimlach
Posts: 5132 - Karma: 14,061
thank you, you learn something new every day haha.
Aug 20 2010 2:00PM
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Shreddysaurus
Posts: 2120 - Karma: 59
You keep saying your knowledge is basic. What the hell do you know? Then we can come up with a problem that will work for you.

Aug 20 2010 2:11PM
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loganimlach
Posts: 5132 - Karma: 14,061
Click for larger image
Aug 20 2010 3:05PM
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Tripplesixty
Posts: 835 - Karma: 148
ok good I'm glad we have two explanations on here now... no more asking how! If you don't get it consult a physics book your high school physics teacher...

And you may continue the theoretical debates of air and wind resistant
Aug 20 2010 3:09PM
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