Kinetic Pressure: Explanation and Questions

  • Thread starter Thread starter Kenny Lee
  • Start date Start date
  • Tags Tags
    Kinetic Pressure
AI Thread Summary
The discussion centers on the calculation of average force exerted by molecules colliding with a wall, questioning the use of round trip time versus collision time. It highlights that the average force is derived from impulse divided by the total time, which includes periods of zero force during travel. Participants suggest that considering a longer duration, like two round trips, could yield different results. The validity of the information from the referenced site and textbooks is acknowledged, but the focus remains on the nuances of the average force calculation. The conversation seeks clarity on the implications of time measurement in kinetic pressure calculations.
Kenny Lee
Messages
75
Reaction score
0
Please visit this site for me. I'm having a little trouble with the explanation.
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kinthe.html#c3
Note however that you can find a similar explanation in all textbooks, so I'm in no way questioning the validity of the information.

The average force that the wall exerts on the molecule is impulse/ time (N's second law). But the time they have made use of, is the time for a 'round trip'. Shouldn't it be the time taken for the collision?
Thans
 
Last edited:
Physics news on Phys.org
Kenny Lee said:
Please visit this site for me. I'm having a little trouble with the explanation.
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kinthe.html#c3
Note however that you can find a similar explanation in all textbooks, so I'm in no way questioning the validity of the information.
The average force that the wall exerts on the molecule is impulse/ time (N's second law). But the time they have made use of, is the time for a 'round trip'. Shouldn't it be the time taken for the collision?
Thans
This is an "average" calculation, assuming there are enough molecules that some are striking the wall at any given time. In terms of individual molecules, the force that one molecule contributes is, say, F during the collision, 0 while it is making the trip to the other wall and back. It's average contribution is the impulse divide by the time of the entire trip. You can, if you like, think of it as "total force"- the actual force times the duration of the collision plus 0 times the duration of the trip- divided by the total time.
 
But couldn't we then make use of the 'average' over a longer period; let's say two 'round trips'. In which case, we would obtain a duration of 4d/v. And a different final result.
Or have I misunderstood?
 

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

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...
View full post »
Thread 'Variable mass system : water sprayed into a moving container'

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}...
View full post »

Similar threads

Work done during a collision -- Change in Kinetic Energy & change in Momentum
Replies
1
Views
2K
Derive Radiation Pressure in terms of N, V, hf
Replies
1
Views
2K
B Collision time interval of a gas molecule with wall of container
Replies
6
Views
2K
Pressure exerted by a gas (derivation using the kinetic theory of gases)
Replies
9
Views
2K
Is atmospheric pressure gravitational or kinetic?
Replies
20
Views
18K
Saturated vapour pressure vapour quality and T-S diagram location
Replies
7
Views
2K
I Question about Momentum vs. Kinetic Energy vs. Deforming In Collisions
Replies
2
Views
2K
I Do smells travel farther in colder or hotter temperatures?
Replies
8
Views
2K
Average velocity of gas molecules in a container
Replies
3
Views
5K
How Is Gas Pressure Derived in the Kinetic Theory of Gases?
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top