Cracking the Mystery of Fermi Numbers - Come Help!

AI Thread Summary
The discussion revolves around estimating the number of hairs on a person's head using Fermi problem-solving techniques. Participants suggest calculating the total by multiplying the number of hairs per unit area by the surface area of the head. Measurements of hair diameter and packing density are recommended to refine the estimate. The conversation emphasizes the importance of both measurement and estimation for accuracy. Overall, the thread seeks collaborative input to tackle this estimation challenge effectively.
Faiza
Messages
96
Reaction score
0
Fermi Numbers!??

I'm trying to solve this problem and explain all my steps in my reasoning.

**HOW MANY HAIRS ARE ON YOUR HEAD?**

If anyone can help me figure this out, reply
thanking u in advance
faiza
 
Physics news on Phys.org
No Replies :( :'(
 
:"( ......
 
No of hairs on head is equal to;

No of hairs per unit area x Surface area of head with hair.

You need to get a value for both of these quantities, either through measurement or estimation (or both).

Claude.
 
this is hard lol
 
Using the average diameter of a hair (about 50 microns, or pluck a few hairs and measure them) you can determine a rough upper limit on the number of hairs. The actual number depends on the packing density, which I think, is not likely less than 10% coverage. So that gives you an approximate lower bound. Pick the mean to get an order of magnitude estimate.
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top