What causes gas particles to accelerate so that P = F / A

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Discussion Overview

The discussion revolves around the concept of gas pressure and the relationship between force, area, and acceleration of gas particles within a container. Participants explore the mechanics of gas particle behavior, particularly during collisions with container walls, and question the underlying causes of particle acceleration.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Vanmaiden questions what causes gas particles to accelerate toward the container walls and proposes the idea of pressure being defined as momentum/area instead of force/area.
  • One participant clarifies that force is related to the rate of change of momentum and that gas particles experience a change in momentum upon colliding with the container walls, which is perceived as force.
  • Another participant points out that the confusion arises from the assumption that gas molecules must be accelerating toward the wall, emphasizing that acceleration is only relevant at the moment of collision when the direction and velocity change.
  • A later reply reinforces the point about the misunderstanding regarding the necessity of acceleration toward the wall for ideal gases.

Areas of Agreement / Disagreement

Participants generally agree on the mechanics of gas particle collisions and the definition of force in relation to momentum, but there is some disagreement regarding the necessity of particle acceleration toward the walls prior to collision.

Contextual Notes

The discussion does not resolve the question of whether pressure could be defined as momentum/area, and assumptions regarding ideal gas behavior are not fully explored.

vanmaiden
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Dear Physics Forums,

Pressure is force / area, and force is mass * acceleration. When you have a gas in a container, it's said to exert a pressure on its container. Therefore, the particles are accelerating toward the container's walls. What's causing these gas particles to accelerate toward the container? Why can't pressure be momentum / area? Momentum, like force, has a tendency to transfer energy as well to a stationary object (the container's walls).

Thank you for addressing my confusion,

Vanmaiden
 
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You are nearly there.

Force = rate of change of momentum.

When a gas particle collides with a container wall it is deflected, suffering a change of momentum (vector change).

This is experienced as a force and a reaction.

The pressure is the aggregate of many such collisions, taken over area and time.
 
Studiot has it. Where you were getting confused is in demanding that the molecule must be accelerating towards the wall. [For an ideal gas we ignore any such effect.] The acceleration occurs when the molecule hits the wall and changes its direction, and therefore its velocity.
 
Where you were getting confused is in demanding that the molecule must be accelerating towards the wall.

Excellent point.
 

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