What is the purpose of a streamlined horizontal position?
Minimizes frontal area and reduces drag.
Define Centre of Mass (CoM)
Point around which body weight is balanced – in swimmers, near the abdomen.
How does arm movement affect CoM?
Arm overhead → CoM toward head; Arm sideways → CoM toward feet.
Define Centre of Buoyancy (CoB)
Centre of displaced water volume around the body.
How does arm movement affect CoB?;
Arm out of water → CoB toward feet;
arm under water → CoB toward head.
Define buoyancy torque
Separation between CoM and CoB that causes rotation of the body in water.
If CoB is closer to head than CoM, what happens?
Feet sink.
If CoM is closer to head than CoB, what happens?
Feet rise.
Why is buoyancy torque important?
It affects horizontal alignment and drag – swimmers must adjust posture.
Which stroke types have smaller CoM/CoB changes?
Opposing arm-leg strokes (e.g. front or back crawl).
Which stroke types have larger CoM/CoB changes?
Synchronized arm-leg strokes (e.g. butterfly or breaststroke).
Effect of large buoyancy torque variation
;Harder to maintain a horizontal body position.
What causes body roll in front/back crawl?
Alternating arm movements create angular rotation (~45°).
Benefits of body roll
Easier breathing, arm recovery, more propulsion, less drag, reduced strain.
Risks of excessive body roll
Possible shoulder injury.
What is the catch phase?
Fingers first enter water – start of stroke and body roll.
What is the pull phase?;
Main propulsive movement pulling water backward to move forward
What forces are created in pull phase?
Vortices, drag, and lift forces.
Which pull pattern is most efficient?
A slight “S” pull – maintains pressure and increases propulsion.
What is the exit or recovery phase?
Arm breaks surface and prepares for next catch while other arm pulls.
How do finger spread and hand angle affect propulsion?
They change drag and water resistance – slight spread and cupped hand are most efficient.
Which laws of motion relate to hand shape?
Newton’s 2nd and 3rd Laws – propulsion depends on force and reaction in water.
In the catch phase, bent or straight arm better?
Bent arm catches more water and reduces shoulder strain.
In the pull phase, straight or “S” pull better
S” pull maintains pressure through stroke path and increases propulsion.
