Podcast
Questions and Answers
What is the official unit of measurement for mass?
What is the official unit of measurement for mass?
What is the official unit of measurement for pressure?
What is the official unit of measurement for pressure?
The pressure exerted on an object is independent of its surface area.
The pressure exerted on an object is independent of its surface area.
False (B)
What is the approximate value of atmospheric pressure at sea level?
What is the approximate value of atmospheric pressure at sea level?
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Atmospheric pressure increases with altitude.
Atmospheric pressure increases with altitude.
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What is the approximate value of hydrostatic pressure at a depth of 10 m in water?
What is the approximate value of hydrostatic pressure at a depth of 10 m in water?
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The air we breathe is primarily composed of oxygen.
The air we breathe is primarily composed of oxygen.
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What is the approximate mass volume of air?
What is the approximate mass volume of air?
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What is the approximate mass volume of freshwater?
What is the approximate mass volume of freshwater?
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The speed of sound in water is faster than the speed of sound in air.
The speed of sound in water is faster than the speed of sound in air.
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Which of the following is NOT a consequence of the refraction of light in water?
Which of the following is NOT a consequence of the refraction of light in water?
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Which of the following is NOT a consequence of the diffusion of light in water?
Which of the following is NOT a consequence of the diffusion of light in water?
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The absorption of light in water is responsible for the gradual decrease in light intensity with depth.
The absorption of light in water is responsible for the gradual decrease in light intensity with depth.
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Pascal's principle states that pressure applied to an enclosed fluid is transmitted undiminished to all points within the fluid.
Pascal's principle states that pressure applied to an enclosed fluid is transmitted undiminished to all points within the fluid.
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Archimedes' principle states that a body immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced by the body.
Archimedes' principle states that a body immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced by the body.
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The buoyant force on an object is independent of the object's volume.
The buoyant force on an object is independent of the object's volume.
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Which of the following is NOT an application of Archimedes principle in freediving?
Which of the following is NOT an application of Archimedes principle in freediving?
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Boyle-Mariotte's law states that, under constant temperature, the volume of a gas is directly proportional to its pressure.
Boyle-Mariotte's law states that, under constant temperature, the volume of a gas is directly proportional to its pressure.
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At constant temperature, the volume of a gas decreases with increasing pressure.
At constant temperature, the volume of a gas decreases with increasing pressure.
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Dalton's law states that the total pressure of a mixture of gases equals the sum of the partial pressure of each gas.
Dalton's law states that the total pressure of a mixture of gases equals the sum of the partial pressure of each gas.
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Henry's law states that the quantity of a gas that dissolves in a liquid is directly proportional to the partial pressure of the gas in the liquid.
Henry's law states that the quantity of a gas that dissolves in a liquid is directly proportional to the partial pressure of the gas in the liquid.
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A gas at saturation is in equilibrium with the surrounding atmosphere.
A gas at saturation is in equilibrium with the surrounding atmosphere.
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What is a thermocline?
What is a thermocline?
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A halocline is usually formed in the same area as a thermocline.
A halocline is usually formed in the same area as a thermocline.
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A halocline can act as a barrier to marine life.
A halocline can act as a barrier to marine life.
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What is the most significant consequence of a halocline?
What is the most significant consequence of a halocline?
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Divers should be aware of thermoclines and haloclines as they pose potential risks to their dives.
Divers should be aware of thermoclines and haloclines as they pose potential risks to their dives.
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What is the name of the effect that describes the apparent change in the size and distance of underwater objects due to refraction?
What is the name of the effect that describes the apparent change in the size and distance of underwater objects due to refraction?
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The size of an object appears larger in water than in air.
The size of an object appears larger in water than in air.
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Objects appear closer in water than in air.
Objects appear closer in water than in air.
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Study Notes
Introduction to Underwater Physics
- This presentation covers the physics fundamental to freediving
- It focuses on the concepts for divers, with specific reference to the Lifras S2 certification.
Fundamental Quantities
-
Mass (M): A measure of matter.
- Unit: kilogram (kg)
-
Force (F): A push or pull, causing movement.
- Unit: Newton (N)
-
Weight (P): Force of gravity on an object.
- Unit: Newton (N)
- Relationship: Weight = mass × 9.81 m/s² (approximately 10 m/s²)
Confusion: Mass and Weight
- Common mistake: conflating mass and weight
- Weight is a force, while mass is a measure of matter
Capacity and Volume
- Capacity: The amount a container can hold.
-
Volume (dm³ & m³): Space occupied.
- 1 dm³ = 1 litre
- 1 m³ = 1000 litres
Density (p)
- Mass density (kg/m³): Mass per unit volume
- Density (solids & liquids): Ratio of a substance's mass to the mass of an equal volume of water at 4°C.
- Density (gases): Ratio of a gas's mass to the mass of an equal volume of air (under the same temperature and pressure conditions).
Pressure (P)
-
Definition: Force applied over a surface area.
- Formula: Pressure = Force/Area (P = F/S)
- Unit: Pascal (Pa)
- 1 bar = 100 000 Pa
Atmospheric Pressure (P
atm )
- Definition: Pressure exerted by the atmosphere.
- Value (sea level): Approximately 1 atm = 1013 hPa = 1.013 bar = 760 mm Hg.
- Variation: Decreases with altitude.
Hydrostatic Pressure (P
hyd )
- Definition: Pressure exerted by a fluid (water) column.
-
Variation: Increases with depth (due to fluid weight).
- Approximately 1 bar for every 10 meters of depth
Relative Pressure
- Definition: Pressure measured relative to a reference value (usually atmospheric pressure).
Absolute Pressure (P
abs )
-
Definition: Total pressure, encompassing atmospheric pressure and hydrostatic pressure.
- Formula: Absolute pressure = Atmospheric pressure + Hydrostatic pressure (P abs = P atm
- P hyd )
Air Composition
-
Air: Mixture of gases.
- Primarily nitrogen (N2) and oxygen (O2).
Water Properties
-
Water Density: Approximately 1000 kg/m³ (fresh water at 4°C)
- Approximate 1033 kg/m³ (salt water)
-
Thermal Conductivity: Water's thermal conductivity significantly exceeds air's, which significantly impacts temperature changes.
- Hence the need for necessary diving gear like wetsuits to maintain warmth
Thermocline and Halocline
- Thermocline: Zone of temperature transition between warm surface water and cooler deeper water.
- Halocline: Zone of salinity transition, impacting the density of seawater.
- Impact of both zones: Can influence environmental factors like visibility and the distribution of marine life
Sound Propagation
- Sound in water and Air: Sound travels much faster in water than in air.
- Directionality of sound: Precise direction determination of sound in water is difficult
Light Phenomena
- Light Travel: Light travels slower in denser mediums.
-
Four Phenomena in Water: Reflection, refraction, diffusion and absorption are notable for how light interacts with water.
- Reflection: light "bounces" off a surface.
- Refraction: light bends when passing through different mediums (like water and air).
- Diffusion: light scattering from particles.
- Absorption: light energy converted into other forms of energy (like heat)
Consequences of Refraction in Diving
-
Distances and Sizes: objects appear closer and larger than they are when viewed under water.
- Apparent distance is about 3/4 of the actual distance
- Apparent size is about 4/3 of actual size
Consequences of Diffusion in Diving
- Visibility: Reduces visibility in water
- Risk/Safety Concerns: Can cause difficulties in evaluating depth
Absorption in Diving
- Light Penetration: Light intensity decreases with water depth.
- Colour Spectrum Penetration: certain colours absorb faster relative to other wavelengths of colour.
Boyle-Mariotte's Law
- Definition: Relationship between pressure and volume of a gas at constant temperature — Inversely proportional (constant temperature)
Dalton's Law
- Definition: Total pressure of a gas mixture equals the sum of the partial pressures of each individual gas.
- Impact on Divers: Applies to the gases in a diver's body.
Henry's Law
- Definition: Dissolved gas amount is directly proportional to the partial pressure of that gas above the liquid, at constant temperature
Applications of Henry's Law
- Diving Accidents: relevant for predicting potential decompression sickness
- Diving Computers: used for calculating effective saturation and decompression schedules
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Description
This quiz covers the essential physics concepts vital for freediving, specifically tailored for the Lifras S2 certification. It delves into fundamental quantities like mass, force, weight, capacity, volume, and density, helping divers enhance their understanding of underwater physics.
