UPSB v3
General Discussion / Physics of Pen Spinning
Science behind pen spinning?
-
Date: Thu, Apr 3 2008 15:54:10
I'm working on a physics project for school, and I decided that I'm going to use pen spinning as my topic.
Do you guys have any examples of physics in penspinning? Specifically, I'm having trouble showing Newton's 2nd Law [ force = mass x acceleration] and rolling friction.
Thanks for the help! (: -
Date: Thu, Apr 3 2008 16:19:41
Force(total amount of forces that used to push the pen)= mass(weight of pen) x acceleration(who knows, calculate by how much amount of force you have applied on the pen)
-
Date: Thu, Apr 3 2008 16:58:44QUOTE (Novastrike @ Apr 3 2008, 12:19 PM) <{POST_SNAPBACK}>Force(total amount of forces that used to push the pen)= mass(weight of pen) x acceleration(who knows, calculate by how much amount of force you have applied on the pen)
That will only work if acceleration is linear.
Pen spinning does not use JUST linear motion.
It moves useing X, Y and Z axis.
You're going to need to research rotaional spin and ANGULAR MOMENTUM. -
Date: Thu, Apr 3 2008 17:28:18QUOTE (jshoeeee @ Apr 3 2008, 11:54 AM) <{POST_SNAPBACK}>rolling friction
Talk about how its better to spin on top of carpet so when you drop your pen it doesn't roll as far away :D -
Date: Thu, Apr 3 2008 19:11:42
There was a site on the physics of pen spinning but it's down now.
2nd Law
1) Anyway, for the 2nd law, you can do a horizontal leigun. If you use a stopwatch, you can measure the time it takes for the pen to travel a certain distance.
2) Then,
v (avg) = d/t
a (avg) = v (avg)/t = d/(t^2)
F (avg) = m*a (avg) = md/(t^2)
Calculates the average force you applied to the pen.
Friction
1) For rolling friction, you can incline a textbook at some angle θ. But at the bottom of the ramp, experiment with different surfaces.
2) If you let the pen go from the top of the ramp, when it reaches the bottom of the ramp (assuming frictionless ramp and rolling motion without slipping):
F = m[a-ramp]
F = m(α-ramp * r)
mg sin(θ) = mr [(ω-bottom^2 - ω-top^2)/(2d)]
where α-ramp is the angular acceleration, r is the radius of the pen, ω is the angular velocity, and d is the distance the pen travels on the ramp.
3) But ω-top = 0.
So, g sin(θ) = r ω-bottom^2/(2d)
4) Rearranging: ω-bottom = root [2d g sin(θ) / r]
5) Now, the pen will start rolling with an initial angular velocity given by ω-bottom.
6) Friction will stop the pen by slowing the angular velocity to a final value ω-final = 0. It does this by causing a negative angular acceleration, α-surface.
α-surface = (ω-final^2 - ω-bottom^2)/2D
where D is the distance the pen travels on the ground before stopping.
7) But ω-final = 0.
So, α-surface = (- ω-bottom^2)/2D
[F(friction)]/ m = a-surface
[F(friction)]/ m = α-surface * r
[F(friction)]/ m = [(- ω-bottom^2)/2D] * r
[µ * mg]/ m = [(- ω-bottom^2)/2D] * r
µ = [(- ω-bottom^2)/2D] * r / g
where µ is the coefficient of friction.
8) Substituting part 3 into 7:
µ = [(- 2d g sin(θ) / 2Dr] * r / g
µ = - d g sin(θ) / D
Because d, g, and θ are constant, you can see that the coefficient of friction really only depends inversely on the distance the pen rolls on the surface, D. And you can physically prove this by doing the experiment with different surfaces.
I may have made a mistake somewhere in the derivation, but you get the point.
Cheers. -
Date: Thu, Apr 3 2008 23:44:25QUOTE (Tialys @ Apr 3 2008, 12:11 PM) <{POST_SNAPBACK}>snip
Wowowow, you're amazing.
Thank you! (:
I might not be able to incoporate some of that stuff into my project, because this is simply an 8th grade physics project, but I'll try to
D Thanks again!
And thanks to everyone else ^___^
I'll try to post up the final vid at the end... if I can... haha -
Date: Fri, Apr 4 2008 03:02:52
Really, you don't want to be doing the physics of pen spinning for an 8th grade project. I was going through it with my physics teacher last year (at age 18 final year physics before university level) and even he was having problems with it. I think he even mentioned there are competing theories on why a spinning object should stay on a surface, as for example in a thumbspin. i.e. Scientists at the top level don't even know all the detail yet!
Edit: Actually, Tialys' description of an experiment using Newton's second law looks easy enough.
You could also do momentum, which is very easy (and related).
Momentum = Mass * velocity
Then show how two different pens, of say masses 10 grams and 20 grams, would have a different momentum while travelling at the same velocity, of say, 3MS-1:
Pen 1: 0.010 * 3 = 0.03 KG MS-1
Pen 2: 0.020 * 3 = 0.06 KG MS-1
Then just say that the second pen, as it has a greater momentum, would take a greater force to stop. This means the pen will maintain its speed during tricks, as a greater friction force is required to stop the momentum the pen has. This causes the pen to be easier to spin. Maybe you could do a graph of various weights of pen and see if there is any trends or something like that? My physics teachers have always loved graphs and then deriving formulas from them.
And just do everything for leigun because you really do not want to be messing about with angular momentums. -
Date: Fri, Apr 4 2008 08:18:45
when do you usually start physics in high school? like grade 10?
-
Date: Fri, Apr 4 2008 08:23:48
8 over here.
-
Date: Fri, Apr 4 2008 11:25:40
you start physics in grade 8, i.e. when you are 13 or 14 years old? We start at age 11 here. -
Date: Fri, Apr 4 2008 15:46:42QUOTE (Mats @ Apr 4 2008, 04:25 AM) <{POST_SNAPBACK}> you start physics in grade 8, i.e. when you are 13 or 14 years old? We start at age 11 here.
Haha well over here, we get an introduction into physics in 8th grade. Then you can choose to take Physics Honors in 11th, or AP in 12th, it really depends on the person.
And thanks!
They're actually several terms that I have to incorporate into my project, and momentum was one of them. I did a backaround to show momentum.
Fortunately, we haven't reached angular momentum yet, so I won't have to incorporate that into the project.
But once again, thanks! (: -
Date: Fri, Apr 4 2008 17:32:49QUOTE (Tialys @ Apr 3 2008, 03:11 PM) <{POST_SNAPBACK}>
You can't do that for a Leigun.
A Leigun contains Horizonal Velocity AND Horizonal Spin.
That spin will affect the displacement, velocity, and time it takes to travel.
You would need to use multiple formulas, or a more relevant formula, since F = MA will not take into consideration the horizonal spin.
AND accelration isn't caused by the RAMP. It's caused by GRAVITY, or, -9.81 m/s^2. -
Date: Fri, Apr 4 2008 21:21:26QUOTE (Xero @ Apr 4 2008, 06:32 PM) <{POST_SNAPBACK}>You can't do that for a Leigun.
A Leigun contains Horizonal Velocity AND Horizonal Spin.
That spin will affect the displacement, velocity, and time it takes to travel.
You would need to use multiple formulas, or a more relevant formula, since F = MA will not take into consideration the horizonal spin.
AND accelration isn't caused by the RAMP. It's caused by GRAVITY, or, -9.81 m/s^2.
Bah, forget the horizonal spin, it won't affect the results very much.
-9.81 m/s^2
Maths was never a strong point of mine, but is it not -9.81ms-2?
i.e. -9.81 metres per second per second not -9.81 metres per (second * second)? -
Date: Sat, Apr 5 2008 00:12:30QUOTE (Mats @ Apr 4 2008, 04:21 PM) <{POST_SNAPBACK}>Bah, forget the horizonal spin, it won't affect the results very much.
-9.81 m/s^2
Maths was never a strong point of mine, but is it not -9.81ms-2?
i.e. -9.81 metres per second per second not -9.81 metres per (second * second)?
this is sooooo getting of the topic of pen spinning lol......
.....what do u actually have to do for your project? is it incorporate actual formulas in a poster or sumithin, or is it just showing examples of laws of physics? -
Date: Wed, Dec 23 2009 17:41:20
I'm doing a senior seminar for university for pen spinning. Does anyone know any good journal articles on the subject?
/Forest -
Date: Wed, Dec 23 2009 23:26:07
Dunno if it still matters anymore, but you could also include Torque in it.
T=Ia
Since T= Fx and I of a thin rod = (mL^2)/2 , then with a few timings and such you could determine forces acting on the pen during a Thumbspin or something
EDIT: wow, i should look at dates huh? xD -
Date: Thu, Dec 24 2009 00:13:24
@ forest
i'm not sure there are ANY good journals on penspinnig, they might have some in japanese but i'm not sure.
also, you can check the UPSB wiki for the online magazine -
Date: Thu, Dec 24 2009 01:49:45
A few Topics
Angular Momentum in 3 dimensions
Torque in 3 dimensions
Equilibrium in 3 dimensions
Acceleration in the 3rd dimension
Free body diagrams Motion-powered LED pens like these http://penwish.com/product_info.php?products_id=755
[tl;dr'd some parts of the thread]
Here we do dumb physics in 8th grade, serious physics in grade 11 and 12.
AP Physics B then C // IB Physics SL then HL.
@above there may be journals on robots doing penspinning, that's a rather difficult AI/robot functioning problem iirc