Estimate the number of hairs in a typical braid

  • Thread starter Thread starter NosajW
  • Start date Start date
  • Tags Tags
    Estimate
AI Thread Summary
A typical human hair is approximately 100 μm in diameter, and the average person has around 100,000 hairs on their head. To estimate the number of hairs in a braid, one can calculate the area of the braid using the formula for the area of a circle, πr², where r is the radius of the braid. A common suggestion for the radius is about one inch, which can help in estimating the total number of hairs. The discussion emphasizes that the question is meant to be an estimation rather than an exact calculation, and participants suggest using online resources for further information.
NosajW
Messages
11
Reaction score
0
A human hair is about 100 μm across. Estimate the number of hairs in a typical braid.
The average number of hairs on a person’s head = 100,000, and the answer is supposed to be 10,000. Can someone explain how you would get 10,000? Thanks in advance
 
Physics news on Phys.org
NosajW said:
A human hair is about 100 μm across. Estimate the number of hairs in a typical braid.
The average number of hairs on a person’s head = 100,000, and the answer is supposed to be 10,000. Can someone explain how you would get 10,000? Thanks in advance

Is this homework? It's not really classical physics. Anyway, I presume you estimate the radius of a ponytail, compute the area pi*r^2, then convert the area into units of hair diameters per m^2.

Now this wouldn't be the densest possible solution but I presume hair is not densely packed.
 
Yeah it's homework and I am taking classical physics so I thought I'd post it here. This is the beginning of the course so we're doing units and basic stuff. This question is ridiculous, how big is the radius of a typical braid supposed to be anyway.
 
NosajW said:
Yeah it's homework and I am taking classical physics so I thought I'd post it here. This is the beginning of the course so we're doing units and basic stuff. This question is ridiculous, how big is the radius of a typical braid supposed to be anyway.

I don't know, try an inch and see what you get. BTW there is a sub forum here for homework problems. Remember, it said estimate. You don't need to get exactly the same answer. But if you want Google average human braid diameter and see if you can find anything.
 
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
Back
Top