Two expressions were used for the drag force experienced by a moving object in a liquid. One depended upon the speed, while the other was proportional to the square of the speed. In which types of motion would each of these expressions be more applicable than the other one?
When the object is moving through a liquid medium, such as water or another viscous liquid, we will apply the Stokes law, which states that the drag force is proportional to velocity.
A force is a factor that can impact an object's motion. A force can cause a mass item to accelerate (e.g., from a standstill).
In general, drag force is proportional to the square of velocity, but in other cases, such as when the object is small, moving slowly, or in a denser medium than air, drag force is related only to the velocity, not the square of velocity.
Animal living on land, if it is not very small, experiences drag force due to air which is proportional to square of the velocity and it is given by
…………………………… ( 1 )
Where, ρ is density of medium i.e., air, C is drag coefficient, A is exposed area of the body and v is velocity.
If the object is moving in air and has a high cross-sectional area, we will utilise the quadratic expression, in which the drag force is exactly proportional to the square of velocity.
The quadratic dependence of air intake on velocity does not hold when the element is small and traveling slowly, or when it is in a medium denser than air. Then the drag force and velocity are directly proportional to each other.
where r is the radius of the body, is the viscosity of the fluid, and v is the velocity of the body, Stokes' law applies.
When comparing creatures that live on land with those that live in water (which is denser than air), equation (1) will only be applicable for enormous species like big fish, dolphins, and even massive whales that have streamlined shapes to lessen drag effects.
(a) What is the maximum frictional force in the knee joint of a person who supports 66.0 kg of her mass on that knee?
(b) During strenuous exercise it is possible to exert forces to the joints that are easily ten times greater than the weight being supported. What is the maximum force of friction under such conditions? The frictional forces in joints are relatively small in all circumstances except when the joints deteriorate, such as from injury or arthritis. Increased frictional forces can cause further damage and pain.
When a glass bottle full of vinegar warms up, both the vinegar and the glass expand, but vinegar expands significantly more with temperature than glass. The bottle will break if it was filled to its tightly capped lid. Explain why, and also explain how a pocket of air above the vinegar would prevent the break. (This is the function of the air above liquids in glass containers.)
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