Change in radius over time for a spherical ball formula

Click For Summary
SUMMARY

The discussion focuses on deriving the change in radius over time for a spherical ball using calculus and the ideal gas law. The volume of a sphere is defined as ##v = \frac{4}{3}\pi r^3##, leading to the relationship $$\frac{dv}{dt} = 4\pi r^2 \frac{dr}{dt}$$. The ideal gas law is applied, resulting in the equation $$Gr\frac{dv}{dt} + Gv\frac{dr}{dt} = Nk \frac{dT}{dt}$$. Participants seek clarification on the algebraic flow and substitutions within these equations.

PREREQUISITES
  • Understanding of calculus, particularly differentiation and the product rule.
  • Familiarity with the ideal gas law and its components.
  • Knowledge of spherical volume calculations and their derivatives.
  • Basic algebra skills for manipulating equations and terms.
NEXT STEPS
  • Study the application of the product rule in calculus.
  • Explore the ideal gas law and its implications in thermodynamics.
  • Learn about the differentiation of geometric formulas, specifically for spheres.
  • Investigate the relationship between temperature changes and volume in gases.
USEFUL FOR

Students and professionals in physics, engineering, and mathematics who are working with thermodynamic equations and calculus applications in spherical geometry.

aspodkfpo
Messages
148
Reaction score
5
Homework Statement
https://www.asi.edu.au/wp-content/uploads/2015/08/NQE_2008_Physics.pdf
Pg 7
Q 12 E)
Relevant Equations
v^r = c dT/dt
P = rG
PV = NkT
1598193191413.png

Algebra in this answer does not seem to flow right. Firstly, the 16, secondly the n term.
Can someone explain or show me the right answer?
 
Physics news on Phys.org
Since big ##V## is used for voltage, denote the volume with little ##v##. You know ##v = \frac{4}{3}\pi r^3##, so $$\frac{dv}{dt} = 4\pi r^2 \frac{dr}{dt}$$Now you will require the ideal gas law,$$pv = (rG)v = NkT$$ Use the product rule when differentiating both sides w.r.t. ##t##,$$Gr\frac{dv}{dt} + Gv\frac{dr}{dt} = Nk \frac{dT}{dt}$$What do you get if you replace ##v## with ##\frac{4}{3}\pi r^3##, and also replace ##\frac{dv}{dt}## with ##4\pi r^2 \frac{dr}{dt}##? Also, it is helpful to note that ##N = nN_A##.
 
  • Like
Likes   Reactions: aspodkfpo

Similar threads

Replies
18
Views
2K
  • · Replies 24 ·
Replies
24
Views
2K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K
Replies
34
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
5
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 5 ·
Replies
5
Views
3K