Why won't pressure on an irregular shape make it move?

In summary, pressure is force per unit area, so if you place an object with say one side twice the area of the other underwater (or even in the atmosphere ) wouldn't there be twice as much force on one side? ( the one with larger area ) and shouldn't that make the object move in the direction of that force?I would love to know what shape you have that has more cross sectional area on one side than the other (as force is directional, cross sectional area is in essence what matters).lets say a wedge, with one edge a bit flator imagine a cone with the top part chopped off and imagine the hole to be solid.A wedge and a cone don't have more cross sectional
  • #1
Idoubt
172
1
This is a very simple doubt, since pressure is force per unit area, if I place an object with say one side twice the area of the other underwater ( or even in the atmosphere ) wouldn't there be twice as much force on one side? ( the one with larger area ) and shouldn't that make the object move in the direction of that force?
 
Physics news on Phys.org
  • #2
I would love to know what shape you have that has more cross sectional area on one side than the other (as force is directional, cross sectional area is in essence what matters).
 
  • #3
lets say a wedge, with one edge a bit flat
 
Last edited:
  • #4
or imagine a cone with the top part chopped off and imagine the hole to be solid.
 
  • #5
A wedge and a cone don't have more cross sectional area on one side than the other...

The sloped side is still exposed to the pressure!

Draw yourself a diagram: use a right triangle triangle sitting on the floor of a tank. Pressure acts perpendicular to each surface, so calculate the magnitude and direction of the forces on the sloped and vertical sides...then calculate the horizontal component of the force on the sloped side...
 
  • #6
As Russ said, the sloped region is still subject to the pressure. Just because it isn't perfectly parallel to the opposite side doesn't mean that the net force is unbalanced. The exercise with the right triangle that Russ mentions is a good way to show this.
 
  • #7
I don't know if this helps, but imagine an air-filled PVC pipe that is capped at each end.
Let's say that the pipe is 3-ft long with an inside diameter of 3-inches.

Go to your favorite swimming pool and force the pipe down as far as practical and then release.

Ver. 1) If held horizontally, then released, the air-filled PVC pipe will rise to the surface horizontally.

Ver. 2) If held vertically, then released, the pipe during ascent will tend to rotate until gaining a complete horizontal configuration. If the water depth is too shallow, the conversion does not significantly alter until complete ascent. If the water depth is deep, the conversion to a horizontal position occurs under water before reaching the surface.
 
  • #8
Now, here is where it gets interesting:

Let's change the shape of the tube from being an elongated circle, to an elongated equilateral triangle.

Back to the swimming pool...

The end result of rotation to a horizontal position remains the same, but now a new factor is introduced, which causes an additional rotation around it's long axis, such to where one of the flat sides eventually points down, the end result being that 2-sides are now rising to and then above the surface.
 
  • #9
With this information in hand, one might ask if it is possible to have both a vertical and lateral movement, at the same time, of a specifically shaped buoyant object underneath a body of water with no other internal/external forces applied.

The answer is yes. It's easy.

Imagine a basketball. Now, affix with strong glue a Plexiglas plate on the top of the basketball that is "wedge shape"... say, higher on the left side and sloping to flat on the right.

Now, introduce weighted materials such to weight balance the left-vs-right Plexiglas wedge.
Then, affix a reasonable weight to the center bottom of the basketball so that it doesn't flip over when submerged in the swimming pool yet can still rise from buoyancy.

There you have it!
During ascent, the ball will move upward by virtue of buoyancy, and laterally by virtue of wedge dynamics against the upper water.

It can be much easier than this, but this explains the potential.
 
Last edited:
  • #10
thank you for the replies, I think I've got it now.
 

Related to Why won't pressure on an irregular shape make it move?

1. Why does pressure not always cause an irregular shape to move?

Pressure is a force that is exerted uniformly in all directions. In the case of an irregular shape, the pressure is not evenly distributed, causing it to stay in place rather than move. The shape may also have other forces acting upon it, such as friction or gravity, which can counteract the pressure and prevent movement.

2. Can pressure ever make an irregular shape move?

Yes, pressure can sometimes cause an irregular shape to move if the force is strong enough to overcome the other forces acting upon the shape. This can happen, for example, if a heavy object is placed on top of the shape, creating enough pressure to displace it.

3. Does the amount of pressure applied affect the movement of an irregular shape?

Yes, the amount of pressure applied can have an impact on the movement of an irregular shape. If the pressure is not strong enough, the shape may not move at all. However, if the pressure is too strong, it may cause the shape to break or deform.

4. Why do some irregular shapes move with less pressure than others?

The ease of movement for an irregular shape depends on a variety of factors, such as its size, weight, and surface texture. A smaller and lighter shape may require less pressure to move, while a larger and heavier shape may need more pressure. Additionally, a smoother surface may allow for easier movement compared to a rougher surface.

5. Is pressure the only factor that affects the movement of an irregular shape?

No, pressure is not the only factor that affects the movement of an irregular shape. As mentioned before, other forces such as friction and gravity can also play a role. Additionally, the shape's material and surrounding environment can also impact its movement. For example, a shape placed on a slippery surface may move more easily than one on a rough surface.

Similar threads

Replies
26
Views
1K
Replies
4
Views
812
Replies
3
Views
1K
Replies
2
Views
969
Replies
13
Views
4K
Replies
10
Views
2K
Replies
7
Views
917
  • Mechanics
Replies
4
Views
2K
Replies
7
Views
1K
Back
Top