Keeping a pencil standing on your hand What physics topics should I research?

In summary, the conversation discusses a scenario where a pencil is standing on a hand and will fall or stand depending on how the hand is moved. The variables involved are the acceleration of the hand, the mass and volume of the pencil, and the change in angle between the pencil and the hand. The question is what topic should be researched to relate the acceleration to the angle changes. Suggestions include the Heisenberg Uncertainty Principle, Newtonian rigid body mechanics, and chaos theory. One person suggests looking into statics and dynamics, while another provides a link to a webpage with a similar scenario.
  • #1
lgmcben
3
0
"Keeping a pencil standing on your hand" What physics topics should I research?

Hi.

My English is not perfect but I'll try my best. This is not a homework. It's a programming question for my simulator project.

Scenario:
- A pencil standing in your hand. It will fall or stand depending on how you move your hand.
- Let's assume that the hand is just an ideal 'plane'.
- Let's assume that a pencil is just a simple, ideal rectangular rigid body object.
- *** Let's assume that a pencil will NOT fall on y-axis. Or in English: It will only fall to the left or right.Variables I have:
- Real-time 'Acceleration' of my hand in x axis. (in m/s/s)
- 'Mass' and 'Volume' of a pencil.

Variables I need:
- The change of 'theta'(angle) between the pencil and my hand(in x-axis) in each time slice. Or you could say d(theta) by d(t)

Questions:
What topic should I research for to relate the acceleration to the angle changes? note:
*** Actually I want to do x,y and z axis but I think if I know how to solve one, I should be able to solve other too.

Thank you in advance! Please let me know if I didn't provide enough information to the problem.
 
Last edited:
Physics news on Phys.org
  • #2


If the pencil were perfectly balanced on its point on an ideal stationary plane (no vibration) and there was absolutely no air motion, the pencil would still fall over in a few seconds, due to the Heisenberg Uncertainty Principle. The combination of Δp (momentum) and Δx (position) in

Δp Δx ≥ h-bar/2 means that if the initial (angular) position is fixed, the uncertainty in (angular) momentum will cause the pencil to fall over.

Bob S
 
  • #3


Bob S is technically correct. However, if you consider a SMALL amount of friction between the pencil and the pivot, then Heisenberg's Uncertainty Principal can be neglected.

First, you must tell us the mass-space distribution of the pencil.
 
  • #4


Either basic Newtonian rigid body mechanics, or chaos theory. Not sure which one you're getting at here.
 
  • #5


you need to explain the situation more in depth
 
  • #6


lgm..
What topic should I research for to relate the acceleration to the angle changes?

the above replies seem focused on the initial instability...but

you do have enough information to develop a formula for the movement of a pencil once it begins.

Likely any introductory college course in statics and (you want this) DYNAMICS would discuss such a falling lever scenario. You'll want to relate the acceleration of the center of mass of the pencil downward from a formula like F = Ma to the movement about the base of the pencil...the vertical (y) movement is obtained from an equation such as d=1/2at2 and I think, but am not sure, that the falling motion of the center of mass is independent of the one pencil end being "anchored"...it's been too many years since I did those kind of problems...

anyway, the above should get you started. good luck.
 
  • #7


Bob S said:
If the pencil were perfectly balanced on its point on an ideal stationary plane (no vibration) and there was absolutely no air motion, the pencil would still fall over in a few seconds, due to the Heisenberg Uncertainty Principle.
...

Bob S

That problem was given in Sakurai, but I got 6 minutes for "reasonable" measures of icepick.
Did you estimate that or did you actually did the math?
 
  • #8

What is the center of mass and how does it relate to keeping a pencil standing on your hand?

The center of mass is the point where an object's mass is evenly distributed. In order to keep a pencil standing on your hand, you must position your hand directly under the center of mass of the pencil. This ensures that the weight of the pencil is evenly distributed and can be supported by your hand.

What role do forces, such as gravity, play in keeping a pencil standing on your hand?

Gravity is the force that pulls objects towards the center of the Earth. In the case of keeping a pencil standing on your hand, gravity is the force that pulls the pencil downward. By balancing the force of gravity with the support of your hand, you can keep the pencil standing upright.

How does the surface area of your hand affect your ability to keep a pencil standing?

The surface area of your hand can affect your ability to keep a pencil standing because it determines the amount of contact between your hand and the pencil. The more surface area in contact with the pencil, the more support it will provide. Therefore, having a larger hand or using the palm of your hand instead of just your fingers can make it easier to keep the pencil standing.

What other factors, besides physics, can impact your ability to keep a pencil standing on your hand?

Other factors that can impact your ability to keep a pencil standing on your hand include the shape and weight distribution of the pencil, as well as any external forces such as wind or vibrations. Additionally, the steadiness and coordination of your hand movements can also affect your success in keeping the pencil standing.

Are there any real-world applications for understanding the physics behind keeping a pencil standing on your hand?

Understanding the physics behind keeping a pencil standing on your hand can have real-world applications in fields such as engineering and architecture. It can also help with tasks that require precision and stability, such as performing delicate surgeries or balancing objects on moving vehicles. Additionally, it can be a fun and impressive party trick!

Similar threads

Replies
13
Views
896
  • STEM Career Guidance
Replies
6
Views
1K
  • STEM Academic Advising
Replies
1
Views
1K
  • STEM Academic Advising
Replies
7
Views
3K
Replies
2
Views
1K
  • STEM Academic Advising
Replies
4
Views
1K
Replies
1
Views
526
  • STEM Academic Advising
Replies
6
Views
782
Replies
2
Views
1K
Replies
18
Views
3K
Back
Top