Weight of water in different vessels

In summary, pressure is a function of depth, not volume, so different shape vessels will have different readings when placed on a weighing scale due to the force being different from the area of the base.
  • #1
Himal kharel
79
0
Water is poured to same level in vessels having different shapes. If pressure is the same at the bottom of each vessel, the force experienced by base of each vessel is same. Why then do these different shape vessels have different readings when placed on weighing scale?
 
Physics news on Phys.org
  • #2
Volume may not be the same. Pressure is a function of depth, not volume, the volume is what the weight depends on. That's my guess.
 
  • #3
Himal kharel said:
If pressure is the same at the bottom of each vessel, the force experienced by base of each vessel is same.
That's true only if the areas of the bottoms of the vessels are the same and ignores downward forces on any other nonvertical surfaces.
 
  • #4
russ watters is certainly right.if the area of the base is less as compared to some other and provided the pressure is kept same, then the weight will be lesser.
but question arises when we consider centre of mass and normal reaction of the vessel with water.
 
  • #5
Watters has it right...

Pressure is force per unit area; observed weight is due to the total volume of water...

You can see this if you consider,say, a three foot tall, 1/2" diameter pipe filled with
water (ignore the weight of the container), and some other very different volume
vessel, say a cylinder, a foot in diameter, of the same height.

Pressure at the bottom is the same, P = hd, but not total weight.
 
  • #6
I guess i didnt explain the question properly. so here is a better explanation.
Consider two cylinders with same base area but one with converging walls and other with diverging walls. let they be filled to same height. now pressure is same at the base as given by P=hdg. So the force on bottom is same as given by force=pressure*area. this suggests that the force on weighing scale given by both cylinders is same. so they must have same readings when placed on scale. but it is not so. Please explain this contradictory result?
 
  • #7
Your vessels aren't holding the same amount of water, so they don't weigh the same. Simple. Additionally, your vessels may weigh differently. If you want it in terms of the pressure, it is because the pressure is [itex]\rho g h[/itex] at the bottom, but [itex]h[/itex] is measured from the bottom of the vessel straight up to the top of the water, so with a container that gets narrower at the top, [itex]h[/itex] decreases as you go away from the center of the base leading to a lower overall force. For a vessel that is wider at the top, you are neglecting the vertical component of the force on the walls of the vessel, which are no longer vertical. This leads to a higher overall force. Of course, no matter how you slice it, it comes down to one vessel having more water in it than the other.
 
  • #8
I think your confusion comes from the difference between the force from the water on the base of the cylinder and the force of the base of the cylinder on the scale, the first depends on the height of the water, the second on the total amount of water and there is no reason for them to necessarily be the same
 
  • #9
I gave the answer in my first post: the water imparts a force on the nonvertical walls and that force is transferred throught the container, to the scale.
 
  • #10
The pressures from the water are contained by the walls of the vessel - no net force, which is why the weight on your scale does not depend on internal pressure, only mass.
 
  • #11
Take any aerosol or gas canister, weigh it, cool it or heat it some and weigh it again. definitely changes internal pressure, but i guarantee it'll weigh the same. Don't heat it up a whole lot though, because they tend to explode. :)
 

1. How does the weight of water change when placed in different vessels?

The weight of water remains the same regardless of the vessel it is placed in. This is because the weight of water is determined by its mass, which does not change. However, the volume of water can vary depending on the shape and size of the vessel it is in.

2. Does the material of the vessel affect the weight of water?

No, the material of the vessel does not affect the weight of water. The weight of water is determined by its mass, not by the material it is contained in.

3. How does the shape of the vessel affect the weight of water?

The shape of the vessel does not affect the weight of water, but it can affect the volume of water. For example, a tall and narrow vessel may hold less water than a short and wide vessel, even though the weight of water in both vessels would be the same.

4. Does the weight of water change with temperature?

The weight of water does not change with temperature. However, the density of water does change with temperature, which can affect its volume. Warmer water is less dense and therefore, has a larger volume compared to colder water of the same weight.

5. How can we measure the weight of water in different vessels?

The weight of water can be measured using a scale or a balance. Place the vessel on the scale, tare it (set the scale to zero), and then add the water to the vessel. The weight displayed on the scale will be the weight of the water in the vessel.

Similar threads

  • Mechanics
Replies
4
Views
2K
Replies
17
Views
9K
  • Introductory Physics Homework Help
Replies
9
Views
877
  • Mechanics
Replies
12
Views
2K
Replies
2
Views
4K
Replies
5
Views
1K
Replies
6
Views
1K
  • Biology and Medical
Replies
10
Views
2K
Replies
5
Views
16K
Replies
10
Views
2K
Back
Top