The physical properties of water contribute to it being the medium of life (its properties sustain living processes)

• The physical properties of water include its buoyancy, viscosity, thermal conductivity and specific heat capacity
  

Buoyancy

• Buoyancy is the upward force applied to an object in a medium and is determined by the density of the medium

• As water is more dense than air, it applies a greater upward force which allows objects to float in water

• The capacity of an object to float in water will be determined by its relative weight (heavier objects will sink)

Viscosity

• Viscosity is a measure of a fluid’s tendency to flow (more viscous fluids are more resistant to flow)

• Water is more viscous than air as it can form hydrogen bonds which increase the friction of flowing molecules

• Additionally, water can dissolve many solutes and these solutes can increase the viscosity of the solution

Thermal Conductivity

• Thermal conductivity is a measure of a medium’s ability to move heat across a temperature gradient

• Water absorbs and transfers heat more readily than air because water particles are packed more tightly together

Specific Heat Capacity

• Specific heat capacity describes the amount of energy required to raise the temperature of 1g of substance by 1ºC

• Water has a higher specific heat capacity than air (highest of any liquid) as its hydrogen bonds require additional energy to break

• The high specific heat capacity of water makes it an effective coolant in sweat (sweat absorbs a lot of thermal energy resulting in a high latent heat of vaporisation)

Physical Properties of Water

Biological Consequences 

The different physical properties of water and air influence the various adaptations and behaviours of terrestrial and aquatic organisms

• The black-throated loon (Gavia arctica) and the ringed seal (Pusa hispida) both live in the Arctic and spend time on land and in the water
  

Black-Throated Loon

• The loon has lighter (less dense) bones, allowing it to float on water (due to buoyancy) – however, the bones are not hollow like in many other birds of flight (allowing it to dive under water)

• Loons have difficulty walking on land because their legs are located at the rear to better propel them through water (higher viscosity)

• The loon’s feathers form an interlocking structure that functions as a barrier to water, preventing heat loss (water has higher thermal conductivity)

Ringed Seal

• The seal has denser bones than the loon, allowing it to stay submerged upon diving (less buoyant)

• The seal possesses a streamlined body to better propel them through water (higher viscosity than air)

• Ringed seals have an outer coat of fur that traps air for waterproofing and also has a thick layer of blubber to prevent heat loss while in water

• Ringed seals do not have many effective cooling mechanisms because water temperatures are generally stable (due to specific heat capacity) – this makes the seal particularly vulnerable to climate change

Arctic Species