Why do the balloons approach each other?

  • Context: Undergrad 
  • Thread starter Thread starter jaumzaum
  • Start date Start date
  • Tags Tags
    Approach
Click For Summary
SUMMARY

The discussion centers on the phenomenon where two balloons approach each other when air is blown between them. The correct explanation involves Bernoulli's principle, which states that as air moves through a restricted area, its speed increases, resulting in a decrease in pressure. This pressure differential creates a net force that pulls the balloons together rather than pushing them apart, countering the initial assumption that increased pressure would separate them. The flow dynamics around the balloons further illustrate how the reduced pressure on the downwind side contributes to their attraction.

PREREQUISITES
  • Understanding of Bernoulli's principle
  • Basic knowledge of fluid dynamics
  • Familiarity with pressure differentials
  • Concept of airflow and its effects on surrounding objects
NEXT STEPS
  • Study the applications of Bernoulli's principle in various fluid dynamics scenarios
  • Explore the concept of pressure differentials in airflow
  • Investigate the effects of airflow on object movement in fluid environments
  • Learn about the principles of aerodynamics and their real-world applications
USEFUL FOR

Students preparing for entrance exams, educators teaching fluid dynamics, and anyone interested in the practical applications of Bernoulli's principle in physics.

jaumzaum
Messages
433
Reaction score
33
I was solving a question from an entrance exam that said the following:
Consider 2 balloons very close to each other. A person blows air in the place at the middle of the 2 balloons. What happens with them?

The answer is that they approach each other, but why? For me, the blow will increase the pressure in the middle of the balloons, that will be greater than the one in the other side, creating a net force that will distance the balloons. What is wrong with this thinking? I tried to use Bernoulli on this one but as I was told, Bernoulli only can be used in the same current line, and I got no response.

Thank you very much!
Joao
 
Physics news on Phys.org
  • Like
Likes   Reactions: Greg Bernhardt and dextercioby
The air tends to follow a convex surface if the speed of the flow and radius of curvature are not excessive. This means the flow is separated on the downwind side of the two balloons, which reduces the pressure. This reduction in pressure affects the flow upwind of the separation. This effect, combined with Bernoulli effect, draws the balloons together.
 
  • Like
Likes   Reactions: HallsofIvy

Similar threads

Graduate Flow of air through an open tube with a balloon
  • · Replies 9 ·
Replies
9
Views
4K
Graduate Optimal Size of Rocket Engine Nozzle for Vacuum Performance
  • · Replies 26 ·
Replies
26
Views
3K
Undergrad Air pressure to energy, am I missing something?
  • · Replies 18 ·
Replies
18
Views
2K
Graduate Difficulty extracting fluid from balloon via syringe
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad Understanding Surface Tension: Laplace's Law and Balloon Experiment Explained
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad How Does the Balloon Analogy Explain the Expansion of the Universe?
  • · Replies 5 ·
Replies
5
Views
1K
High School Why does a frozen balloon have this structure?
  • · Replies 3 ·
Replies
3
Views
2K
Clarifying the Definition Total/Stagnation Pressure (p₀) in Bernoulli'
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Why does my ball launcher spin the ball and not launch it (air)?
  • · Replies 5 ·
Replies
5
Views
1K
Undergrad Pressure differences in a leaking vacuum vessel
  • · Replies 17 ·
Replies
17
Views
10K