Hydrodynamics and Basic Skills Flashcards

A swimmer's legs tend to sink, causing an increase in drag. This is primarily due to the relationship between which two hydrodynamic principles?

Answer: Center of Buoyancy and Center of Gravity

The center of gravity (mass) in a human is typically lower, around the hips, while the center of buoyancy is higher, around the chest, due to air in the lungs. This separation creates a torque that causes the denser legs and hips to sink, rotating the body out of a streamlined horizontal position and increasing drag.

A Water Safety Instructor is teaching a student the importance of a streamlined push-off from the wall. Which type of drag is most significantly reduced by maintaining a tight, streamlined position during a glide?

Answer: Form Drag

Form drag (or pressure drag) is the resistance created by a swimmer's shape and cross-sectional surface area as they move through the water. A tight streamline minimizes this surface area, allowing the swimmer to cut through the water more efficiently, thus reducing form drag. While other drags exist, form drag is the most profoundly impacted by body position and shape.

Which of the following best describes the application of Newton's Third Law of Motion to swimming?

Answer: As a swimmer's hands and arms push the water backward, the water pushes the swimmer forward.

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. In swimming, the 'action' is the swimmer pushing water backward with their hands, arms, and feet. The 'opposite reaction' is the water pushing the swimmer's body forward, creating propulsion.

During a lesson on treading water, a student is struggling using the flutter kick and is tiring quickly. Which of the following kicks would be most effective and efficient for the student to maintain a vertical position?

Answer: Rotary (Eggbeater) Kick

The rotary, or 'eggbeater', kick is the most efficient and effective method for treading water. It provides continuous upward support because one leg is always in the power phase of the kick. The flutter kick is generally inefficient for sustained treading.

A swimmer is performing the front crawl with their head lifted too high. What is the most likely hydrodynamic consequence of this error?

Answer: It causes the hips and legs to drop, increasing form drag.

Lifting the head high while swimming the front crawl disrupts the body's horizontal alignment. This action causes the hips and legs to drop lower in the water, which significantly increases the body's frontal surface area and, consequently, form drag. This makes swimming much less efficient.

According to Archimedes' principle, the upward buoyant force that is exerted on a body immersed in water is equal to the:

Answer: Weight of the water the body displaces.

Archimedes' principle states that the buoyant force on a submerged or floating object is equal to the weight of the fluid displaced by the object. This principle explains why people float and is a fundamental concept in hydrodynamics.