Pressure Difference between 70ft and 40ft

[scubadiver1973]

What's the pressure difference on your ears between 40ft and 70 ft ?

 

[Gombessa]

It's roughly one atmosphere difference (33ft is 2ATM, 66ft is 3ATM).

 

[sea2summit]

40'
40'/33'=1.21
1.21 + 1 = 2.21 ATA
2.21x14.7=32.49PSI

70'
70'/33'=2.12
2.12+1=3.12ATA
3.12x14.7=45.86PSI

45.86PSI-32.49PSI=13.37PSI

If you mean between your ear's that's all diver dependent:shocked2:

 

[gypsyjim]

You are under roughly 50% more pressure when you are at 70ft than at 40. Very roughly.

 

[boulderjohn]

While it is, indeed, roughly one atmosphere, the impact on your ears in that one atmosphere of change is different from the impact of the same amount of change at other depths.

If you had a flexible container filled with air (essentially like your ears) at the surface, it would be under one atmosphere of pressure. If you took it to 33 feet of sea water, it would be under two atmospheres of pressure. The impact on its size would be the reciprocal of the number of atmospheres. That means that the container would now be 1/2 the size it was on the surface. If you then continued down to 66 feet, that container would now be at 3 atmospheres of pressure, and its size would be reduced to the reciprocal of that, or 1/3.

That means that in that first atmosphere of change, the size was reduced by one half. In the next atmosphere of change, it went from 1/2 to 1/3, so it was only reduced by 1/6. In the next 33 feet, it would go from 1/3 to 1/4, so it would be reduced by only 1/12.

That is why the impact on your ears of changes in depth is so much greater when you first start to descend then when you are in deeper water.

 

[Garrobo]

I don't know the technical stuff about pressure on one's ears at depth but in my case it feels like there is less pressure the deeper I go. The reason I say this is that once I get below about 30 or 40 feet it is much easier for me to clear my ears. At shallower depths I need to hold my nose to clear my ears but the deeper I go I can clear them just by exhaling through my nose. Doesn't make sense.

 

[herman]

What's the pressure difference on your ears between 40ft and 70 ft ?

If you are clearing properly the answer is 0. Pressure difference between the inside and the outside of your eardrum is what causes pain, if you are clearing properly there is no differential pressure, reguardless of depth. Now if your asking what is the diffenence in ambient pressure on the body between the 2 depths, see above.

 

[gypsyjim]

Very well put Herman. Better answer to his underlying question, I think than mine.

 

[gypsyjim]

I don't know the technical stuff about pressure on one's ears at depth but in my case it feels like there is less pressure the deeper I go. The reason I say this is that once I get below about 30 or 40 feet it is much easier for me to clear my ears. At shallower depths I need to hold my nose to clear my ears but the deeper I go I can clear them just by exhaling through my nose. Doesn't make sense.

As pointed out above this is because descending that first 33 feet creates the greatest relative pressure difference, as you have doubled the pressure that you are under at the surface. The next 33 feet also adds another atmosphere of pressure, but this increase is now only a 50% increase over the relative pressure you were under at 33 feet.
As Herman points out, if you continually clear you should not notice this difference, but if you are slow to clear it becomes quickly apparent.
It is for these same reasons that on ascent the greatest expansion of air in our bodies and BCD's occurs in those last 33 ft!

 

[acamato]

Every foot of freshwater = 0.433 PSI

Saltwater will be a little greater due to the density difference.