Understanding Pressure and Force in Hydraulic Systems

  • Context: High School 
  • Thread starter Thread starter phy1210
  • Start date Start date
  • Tags Tags
    Pressure
Click For Summary

Discussion Overview

The discussion revolves around the concepts of pressure and force in hydraulic systems, particularly focusing on a scenario involving two identical stone tiles positioned differently and a water bottle. Participants explore the relationship between pressure, force, and area, and how these principles apply in different contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant defines pressure as force per unit area and discusses how applying a small force on a hydraulic pedal results in a larger force on the brakes.
  • Another participant questions the pressure differences between two identical tiles, one vertical and one horizontal, suggesting that pressure should be the same while forces differ.
  • Some participants agree that the forces acting on the tiles are equal since they are identical, but they express confusion about how pressure can differ under these conditions.
  • There is a discussion about the equation for pressure (Pressure = Force/Area) and how it implies that if force is constant and area changes, pressure will vary accordingly.
  • A participant brings up the example of a water bottle, questioning whether pressure is the same on different surfaces despite varying areas, leading to further exploration of how pressure behaves in liquids and gases.
  • Another participant compares the situation to a sailboat, explaining that while pressure may be consistent, the larger area of a sail generates more force, which adds complexity to the understanding of pressure in different contexts.

Areas of Agreement / Disagreement

Participants generally agree that the forces acting on the tiles are the same, but there is no consensus on how pressure can differ between the two tiles or in the water bottle example. The discussion remains unresolved regarding the relationship between pressure, force, and area in these scenarios.

Contextual Notes

Participants express uncertainty about the implications of pressure being defined as force per unit area, particularly in scenarios involving different surface areas. There is a lack of clarity on how pressure behaves in static fluids and gases, and how this relates to the forces acting on surfaces of varying areas.

phy1210
Messages
10
Reaction score
0
Pressure is defined as the force acting per unit area.

If we take a hydraulic system of a car, the pressure that will be acting on both piston will be the same. If we apply a small force on the pedal, it will result in a bigger force on the brakes.

Here is a multiple choice question that is troubling me:
There are 2 identical stone tiles. One is vertical (Small surface area acting on the ground) and the other is horizontal (Large surface area acting on the ground).

Through the above definition, I would say the pressure is the same while the forces are different. But the answer was that the pressure was different and the forces are the same. Could you explain the answer?

Thanks in advance!
 
Physics news on Phys.org
welcome to pf!

hi phy1210! welcome to pf! :smile:
phy1210 said:
There are 2 identical stone tiles. One is vertical (Small surface area acting on the ground) and the other is horizontal (Large surface area acting on the ground).

Through the above definition, I would say the pressure is the same while the forces are different.

hint: what are the forces on each of the tiles? :wink:
 
Thanks tiny-tim!

I forgot to mention that they are identical tiles. We can deduce that they have the same forces. But how can the pressure be different then?

They have the same pressure acting per unit area, isn't?
 
Last edited:
phy1210 said:
We can deduce that they have the same forces.

yes: the forces are the weights, so they are the same :smile:
But how can the pressure be different then?

physics is equations …

so what is the equation for pressure? :wink:​
 
Pressure=Force/Area

If the force is the same and area is smaller, the pressure will be higher and vice versa.

I understand this part!

Lets take a water bottle. Pressure on the wall of the bottle and on the cap is the same despite different surface areas?
 
phy1210 said:
Lets take a water bottle. Pressure on the wall of the bottle and on the cap is the same despite different surface areas?

pressure (+ ρgh) is the same everywhere in a stationary liquid
 
Pfff... I am not being able to convey what I don't understand!

If there was no water in the bottle. Air molecules would collide at the same rate everywhere inside the bottle.

If we take the cap:
Area is small
Force is the same
Hence, Pressure is high

If we take the base of the bottle:
Area is bigger
Force is the same
Hence, Pressure is low

But as pressure is defines as force per unit area

These 2 regions will have the same force per unit area and hence they will have the same pressure.
 
phy1210 said:
If we take the cap:
Area is small
Force is the same
Hence, Pressure is high

If we take the base of the bottle:
Area is bigger
Force is the same
Hence, Pressure is low

But as pressure is defines as force per unit area

These 2 regions will have the same force per unit area and hence they will have the same pressure.

Think about the sail of a sailboat. The pressure on the sail comes from air molecules hitting the sail, just as the pressure in the bottle comes from air molecules hitting the inside of the bottle. The pressure is the same (the air molecules are hitting just as hard) on a big sail as a little sail, but a big sail generates more force and can drive a bigger boat.

So it should be:
If we take the cap:
Area is small
Pressure is the same
Hence, Force is lower

If we take the base of the bottle (same wind, bigger sail):
Area is bigger
Pressure is the same
Hence, Force is higher
 
I think I got it now.

Thanks for your help, tiny-tim and nugatory.
 

Similar threads

High School How hydraulic pressure can change the magnitude of a force?
  • · Replies 7 ·
Replies
7
Views
1K
Undergrad Resulting force on a chamfered pneumatic piston
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Distributed Forces and force density....
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad Sound pressure and inverse distance law
  • · Replies 5 ·
Replies
5
Views
3K
High School Torque Calculation - Not a basic application
  • · Replies 37 ·
2
Replies
37
Views
3K
Undergrad Hydrostatics: Pascal's principle and ocean depth
  • · Replies 13 ·
Replies
13
Views
3K
Undergrad How viscous forces affect force transmission in hydraulic systems.
  • · Replies 3 ·
Replies
3
Views
2K
High School Trying to understand hydrostatic pressure
  • · Replies 20 ·
Replies
20
Views
2K
High School Friction and Newton's laws in car braking systems
  • · Replies 10 ·
Replies
10
Views
2K
Undergrad Why constant pressure over different shapes produces the same force?
  • · Replies 18 ·
Replies
18
Views
2K