{"id":67,"date":"2024-09-03T16:47:21","date_gmt":"2024-09-03T16:47:21","guid":{"rendered":"https:\/\/courses.asiascubainstructors.com\/?post_type=lessons&p=67"},"modified":"2024-09-13T16:44:11","modified_gmt":"2024-09-13T16:44:11","slug":"physics-2-pressure-and-volume","status":"publish","type":"lessons","link":"https:\/\/courses.asiascubainstructors.com\/de\/lessons\/physics-2-pressure-and-volume\/","title":{"rendered":"Restricted content"},"content":{"rendered":"

[et_pb_section fb_built=”1″ _builder_version=”4.16″ _module_preset=”fce115cd-1d70-4a47-a81f-fb76bc656147″ background_color=”RGBA(255,255,255,0)” custom_margin=”||||false|false” custom_padding=”0px||||false|false” bottom_divider_height=”49px” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_row use_custom_gutter=”on” gutter_width=”1″ make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_color=”#4E70C9″ background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”3%|3%|3%|3%|true|true” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.22.0″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”8b1f8231-1210-4c64-bae4-d177be5c655c” text_text_color=”#FFFFFF” header_2_text_color=”#FFFFFF” header_3_text_color=”#FFFFFF” header_4_text_color=”#FFFFFF” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Physics<\/h1>\n

 <\/p>\n

2. Pressure and volume<\/h2>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row admin_label=”Class Details Area” _builder_version=”4.22.0″ _module_preset=”default” hover_enabled=”0″ use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content” custom_padding=”10%||||false|false” sticky_enabled=”0″][et_pb_column type=”4_4″ _builder_version=”4.22.0″ _module_preset=”default” custom_padding=”||||false|false” custom_padding_phone=”|5%||5%” custom_padding_last_edited=”off|desktop” hover_enabled=”0″ global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content” sticky_enabled=”0″][et_pb_text _builder_version=”4.22.0″ _module_preset=”8b1f8231-1210-4c64-bae4-d177be5c655c” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Pressure<\/h3>\n

Pressure is measured in bar or atmospheres (atm), which are essentially the same.<\/p>\n

Gauge pressure<\/strong><\/em> is the pressure of the water at a given depth (not counting the atmospheric pressure).
A pressure gauge on a scubatank shows gauge pressure. It will show zero when the tank is empty.<\/p>\n

Absolute<\/strong><\/em> or Ambient pressure<\/strong><\/em> is the water pressure plus the atmospheric pressure. (At sea level the atmospheric pressure is 1 bar\/atm).<\/p>\n

Pressure increases in seawater by 1 bar every 10 metres.
Pressure increases in fresh water by 1 bar every 10.3 metres.<\/p>\n

Pressure increases in fresh water by 0.97 bar every 10 metres.<\/p>\n

 <\/p>\n

 <\/p>\n

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\ue007<\/span>
<\/strong><\/span><\/p>\n

Examples<\/strong><\/span><\/p>\n

To calculate gauge pressure in bar, simply divide the depth of the water by 10 for seawater and by 10.3 for fresh water.<\/p>\n

<\/strong><\/p>\n

Examples:<\/strong>
<\/span><\/p>\n

To calculate the gauge pressure at 37m in sea water.
37 \u00f7 10 = 3.7 bar.<\/em><\/p>\n

To calculate the gauge pressure at 16m in fresh water.
16 \u00f7 10.3 = 1.55 bar.<\/em><\/p>\n

To calculate the absolute\/ambient pressure in bar simply repeat the above procedure and then add 1 (providing you are calculating for sea level).<\/p>\n

Examples: <\/strong>
To calculate the absolute pressure at 37m in sea water.
37 \u00f7 10 = 3.7 bar.
3.7 + 1 = 4.7 bar.<\/em><\/p>\n

To calculate the absolute pressure at 16m in fresh water.
16 \u00f7 10.3 = 1.55 bar.
1.55 + 1 = 2.55 bar.<\/em><\/p>\n

In most questions in physics of diving you will use absolute pressure in your calculations. Except if they specifically<\/span> ask you for the gauge pressure.<\/p>\n

<\/span><\/p>\n

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Pressure and volume<\/h3>\n

You cannot compress a liquid or a solid by applying greater pressure, but you can compress a gas as the molecules are further apart.
The volume of a gas is inversely proportional to the surrounding pressure on the gas, meaning that the volume will double if the pressure becomes half, and vice versa.<\/p>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row use_custom_gutter=”on” gutter_width=”1″ make_equal=”on” admin_label=”Class Details Area” _builder_version=”4.16″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”50px|0px|0px|0px|false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”|5%||5%” custom_padding_tablet=”” custom_padding_phone=”|5%||5%” custom_padding_last_edited=”on|phone” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”8b1f8231-1210-4c64-bae4-d177be5c655c” background_color=”#ffffff” custom_padding=”5%|5%|5%|5%” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

\ue007<\/span>
<\/strong><\/span><\/p>\n

Examples<\/strong><\/span><\/p>\n

If you take an inverted bucket down to 20m seawater what would the volume of the air be inside it?
Pressure = 1 x 3
Volume = \u2153<\/em><\/p>\n

If a balloon contains 15 litres of air at the surface; what would its volume be if taken down to 40m in seawater?
Pressure = 5 bar.<\/em>
15 \u00f7 5 = 3 litres.<\/em><\/p>\n

If a balloon contains 7 litres of air at 30m in seawater and is then taken to the surface; what would its volume then be?
7 x 4 = 28 litres.<\/em><\/p>\n

Ask yourself a question \u2013 will the balloon get bigger or smaller? Then you will know whether to multiply or divide.<\/p>\n

 <\/p>\n

In fresh water it will be similar. Just remember, the pressure increases with 0.97 bar every 10 meters:<\/p>\n

Examples:<\/strong><\/p>\n

If a balloon contains 15 liters of air at the surface, what would its volume be if taken down to 40 meters in fresh water?<\/p>\n

Pressure = 1 + (4 \u00d7 0.97) = 4.88 bar<\/em>
Volume = 15 \u00f7 4.88 = 3.07 liters.<\/em><\/p>\n

If a balloon contains 7 liters of air at 30 meters in fresh water and is then taken to the surface, what would its volume be?<\/p>\n

Pressure at 30 meters =\u00a0 1 + 2.91 = 3.91 bar<\/em>
Volume = 7 \u00d7 3.91 = 27.4 liters.<\/em><\/p>\n

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<\/span>
\n<\/strong><\/span><\/p>\n

Tip<\/strong><\/span><\/p>\n

A balloon is sometimes called a flexible container. A scuba tank is referred to as an inflexible container \u2013 a scuba tank does not change volume or the amount of air it holds when changing depth.[\/et_pb_text][et_pb_text _builder_version=”4.22.0″ _module_preset=”8b1f8231-1210-4c64-bae4-d177be5c655c” background_color=”#ffffff” custom_padding=”5%|5%|5%|5%” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

\ue007<\/span>
<\/strong><\/span><\/p>\n

Examples<\/strong><\/span><\/p>\n

If you move from one depth to another, it\u2019s easiest to take it first to the surface and then back down to the new depth.<\/p>\n

Example:<\/strong>
You take a balloon containing 5 litres of air from 35m up to 15m in seawater, what would its new volume be?
5 x 4.5 = 22.5 litres at the surface, then take it back down to 15m<\/em>
22.5 \u00f7 2.5 = 9 litres at 15m.<\/em><\/p>\n

And the same problem in fresh water:
5 x 4.395 = 21.975 litres at the surface.<\/em>
21.975 \u00f7 2.455 = 8.95 litres at 15m<\/em><\/p>\n

<\/span><\/p>\n

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Pressure and Absorption of Gases<\/h3>\n

If the pressure of a gas in contact with a liquid is increased the gas will dissolve into the liquid until a state of equilibrium is reached. (Saturation<\/strong><\/em>).
If the pressure of a gas in contact with a liquid is decreased the gas will come out of the liquid (supersaturation<\/strong><\/em>) if this happens quickly bubbles will form in the liquid.<\/p>\n

A diver’s body can be considered a gas (in your lungs) in contact with a liquid (your body).
The way your body absorbs and releases gases is the principle that explains\u00a0decompression sickness<\/em>.<\/p>\n

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Pressure, Temperature & Volume relationships<\/h3>\n

As a rule of thumb, in a scuba tank the pressure changes by 0.6 bar the for every degree Celsius change.
For flexible containers like balloons, the pressure remains the same and the volume changes.<\/p>\n

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\ue007<\/span>
<\/strong><\/span><\/p>\n

Examples<\/strong><\/span><\/p>\n

A scuba tank is filled to 200 bar at 15 degrees Celsius, it is then left in the sun at a temperature of 30 degrees Celsius \u2013 what would the pressure in the tank now be?
30 \u2013 15 = 15 degrees change <\/em>
15 x 0.6 = 9 bar change upwards <\/em>
New pressure = 209 bar.<\/em><\/p>\n

A scuba tank is filled to 210 bar at a temperature of 35 degrees C and is then taken into water of 5 degrees C what would the pressure in the tank now be?
35 \u2013 5 = 30 <\/em>
30 x 0.6 = 18 <\/em>
210 \u2013 18 = 192 bar.<\/em><\/p>\n

<\/span><\/p>\n

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