What are the forces acting on the container?

[jbriggs444]

I stated that as soon as you open the hole pressure goes down. If pressure goes down force must also go down. That's math.

Force is a vector. Pressure has gradients. You cannot compute total force by multiplying total surface area by average pressure.

If you reduce pressure on one side of the pipe, net force goes up, not down.

Pressure gradient force is a potential force. Like buoyancy. You push down a less dense object into water giving potential energy. You let go and the object moves upwards but does not apply a force in the opposing direction.

A gradient is the opposite of a potential.

The if a vector field is the "gradient" of a scalar field, then the vector field is conservative and the scalar field is the "potential" of the vector field.

 

[Chuzzled]

Force is a vector. Pressure has gradients. You cannot compute total force by multiplying total surface area by average pressure.

If you reduce pressure on one side of the pipe, net force goes up, not down.

A gradient is the opposite of a potential.

The if a vector field is the "gradient" of a scalar field, then the vector field is conservative and the scalar field is the "potential" of the vector field.

Force is a vector. Pressure has gradients. You cannot compute total force by multiplying total surface area by average pressure.

If you reduce pressure on one side of the pipe, net force goes up, not down.

A gradient is the opposite of a potential.

The if a vector field is the "gradient" of a scalar field, then the vector field is conservative and the scalar field is the "potential" of the vector field.

How does net force go up. Force =pressure*surface area. That’s a fact. https://www.dummies.com/education/science/physics/how-to-calculate-force-based-on-pressure/

When you open the hole, volume is increased and pressure is decreased. That’s a fact. http://www.westfield.ma.edu/cmasi/gen_chem1/Gases/ideal gas law/pvnrt.htm

You need energy to create a pressure gradient and then once you have such gradient, pressure gradient force takes over. The rocket utilized the energy from combustion reaction to create pressure. A vacuum cleaner uses a propeller to creat pressure gradient. So yes it is potential energy.

Pressure gradient force is a vector. That’s a fact. https://www.shodor.org/os411/courses/_master/tools/calculators/pgf/index.html

 

[jbriggs444]

How does net force go up. Force =pressure*surface area. That’s a fact.

Force is a vector. That is a fact also. The net force from equal pressure on the six faces of a cube is zero.

To get the net force you find the forces on each face and add them all up as vectors.

 

[Chuzzled]

Force is a vector. That is a fact also. The net force from equal pressure on the six faces of a cube is zero.

To get the net force you find the forces on each face and add them all up as vectors.

Sure if you want to put it that way. But there is still force applied to all six walls. If the walls were elastic like a balloon, the pressure force would cause the walls to stretch.

But as soon as air starts coming out you will notice the balloon walls contracts. If there was an uneven force, you would see it on the balloon walls. Instead you see all the walls contract evenly

 

[jbriggs444]

Sure if you want to put it that way. But there is still force applied to all six walls. If the walls were elastic like a balloon, the pressure force would cause the walls to stretch.

But as soon as air starts coming out you will notice the balloon walls contracts. If there was an uneven force, you would see it on the balloon walls. Instead you see all the walls contract evenly

Nope. There is an asymmetry. There is a hole in one wall. That wall is subject to less force than the rest. That means that there is an unbalanced net force. The balloon moves as a result.

 

[Chuzzled]

Nope. There is an asymmetry. There is a hole in one wall. That wall is subject to less force than the rest. That means that there is an unbalanced net force. The balloon moves as a result.

How can eliminate the possibility of the exhaust pushing off the atmosphere. Do you have a simple experiment to demonstrate this?

 

[jbriggs444]

How can eliminate the possibility of the exhaust pushing off the atmosphere. Do you have a simple experiment to demonstrate this?

The simplest experiment is hazardous. Place a compressed air cylinder on its side and break off the valve. The resulting force is larger than atmospheric pressure multiplied by area of the hole. A loose cylinder can break through walls and wreak havoc.

In addition, the scenario introduced in post #1 in this thread involves vacuum, not atmosphere.

A quick trip to Google finds

 

[russ_watters]

Can you prove that? As soon as you open the hole, pressure decreases and the force applied to all walls decreases as a result.

What you said cannot be observed in reality. Let’s say you have a pipe with only one end open. You put a small hole on the side of the pipe near the closed end. You use vacuum near the open end to create a pressure gradient cause air to move out of the pipe. Why doesn’t the pipe move forward or at least have some thrust?

Can you create a simple experiment proving what you have stated?

Oh, we had this a few months ago - a silly youtube video of someone preventing a balloon rocket or something from moving with a vacuum cleaner. We're not going to indulge this. If you want to learn how rockets work, we can teach you, but you need to accept the teaching, not play silly games. Feel free to start a new thread, but only if you are going to accept and learn the actual physics. With diagrams and math and straightforward real world examples. No games with silly, purposely convoluted examples and no argementativeness.

Thread closed.