Angled Rod w Float Attached -- Force of Float

[mrapple]

Hi!

A ridged rod is submerged in water at a 45 degree angle toward the bottom of a tank of water. The upper end of the rod is fixed to a pivot point and so, the lower end of the rod is able to move around that pivot point. The lower end of the rod has a float attached to that displaces 50lb of water. The rod length is 15 feet. How do I calculate how many Lb of upward force the float has at any given point along its' journey upwards toward the surface. Thanks!

 

[berkeman]

Welcome to PF.

What is the application? Is the upper hinge attached to a dock or something?

 

[Baluncore]

The float will always have a vertical buoyant force of 50 lbs due to it's displacement.
But we don't know the float density, or how much the float weighs.

 

[kuruman]

According to Archimedes' principle, the float exerts an upward force on whatever is attached to it that is equal to the weight of the water it displaces. How much water weight does the float displace?

 

[Baluncore]

How much water weight does the float displace?

The lower end of the rod has a float attached to that displaces 50lb of water.

If the float has a density over one, or a mass of 50 lbs or more, it will sink.

 

[kuruman]

If the float has a density over one, or a mass of 50 lbs or more, it will sink.

Forgive me, but a float that sinks would not be called a "float"; it could be called a "sinker". I think the intention of the problem's author is that the float exerts an upward force of 50 lbs. Otherwise, we would be provided with more information. It is entirely possible that @mrapple , being new, has not provided all there is.

 

[Baluncore]

I think the intention of the problem's author is that the float exerts an upward force of 50 lbs. Otherwise, we would be provided with more information.

Then the question:

How do I calculate how many Lb of upward force the float has at any given point along its' journey upwards toward the surface.

is answered.

I suspect, once the correct question is identified, the answer will include;
Force = buoyancy * Cos( declination angle )

 

[berkeman]

I suspect, once the correct question is identified, the answer will include;
Force = buoyancy * Cos( declination angle )

Agreed. After lots more personal research on my part, I think I've decoded the OP's question...

http://waynesthisandthat.com/birds.html

 

[mrapple]

Then the question:

is answered.

I suspect, once the correct question is identified, the answer will include;
Force = buoyancy * Cos( declination angle )

Do I use Sin instead if the angle is decreasing right?

 

[Baluncore]

Do I use Sin instead if the angle is decreasing right?

That will depend on which way you measure the angle, from the vertical or the horizontal. But if the angle is 45°, it does not make any difference.

 

[mrapple]

Terms to google

I am trying to produce a water fed engine. This isn't homework. I do not have a physics degree. I can't find the answer online as when you google equilibrium they all refer to a situation where the rod is perpendicular to the ground. You said it won't make a difference at a 45 degree angle. What if the 1st class lever is at a 60 degree angle and is outside of the tub of water (i.e. just in the air). Can you give me some directions as to terms to google or what equations should I use?

Thanks

 

[berkeman]

I am trying to produce a water fed engine.

Do you mean like a water turbine to generate electricity, or a perpetual motion machine?

 

[mrapple]

Turbine. Perpetual motion machines don't work

 

[mrapple]

I know that force times distance on each side is used to calculate equilibrium. What I am trying to figure out is if the heavier side will always cause it to point straight downward or somewhere in between at an angle not perpendicular to the ground?

 

[pbuk]

If the the lever is not balanced then unless there is some other constraint you have not mentioned it will reach equilibrium only when it is vertical.

 

[jbriggs444]

I know that force times distance on each side is used to calculate equilibrium. What I am trying to figure out is if the heavier side will always cause it to point straight downward or somewhere in between at an angle not perpendicular to the ground?

Without a drawing, it is hard to guess what you mean. Perhaps there is a float in the water and a weight attached to a portion of the rod that extends out of the water. In that case, I see no possibility for a stable equilibrium other than directly vertical or flat horizontal.

What is the rod + float expected to do anyway? Control a throttle valve or fill valve?

 

[pbuk]

Without a drawing, it is hard to guess what you mean.

Yes, I think a drawing and an explation of what you are trying to do (rather than what you are trying to calculate) is needed.