QUIZ 1.Define momentum 2.How can a bullet and a bus have the same momentum. 3.Why are stroke length and stroke rate important in swimming? 4.Give an example of how force summation can be seen in freestyle. 5.The greater the summation of force the greater the…. Explain. 6.What role does impulse play in production of force in freestyle?

Fluid Mechanics Year 11 PE - Miss Ramsay

Learning intention To apply fluid mechanics to analyse and evaluate swimming technique.

Concepts Buoyancy – Centre of buoyancy Propulsion – Lift – Drag Fluid resistance – Skin – Water

Buoyancy Archimedes Principle states “that any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force the magnitude of which is equal to the weight of the fluid displaced by the body” - Britannica (2014)

Propulsion

Bernoulli’s Principle Systems of low and high pressure cause a combination of effects know as lift and drag This can be easiest related to how a plane fly’s

LIFT and DRAG and wing design

Pulling and pushing forces

Lift

Propulsion and swimming Why might drag be considered an impeding concept in most sports? Does this apply to swimming? How can drag be minimised and maximised at the same time?

Drag

Which athlete has more impeding drag force and ultimately less propulsion? How can this be improved?

Result of legs dropped and head raised

Fluid Resistance Forms of resistance: Skin resistance Turbulence resistance Wave resistance

Skin resistance When a swimmer moves through the water, the fluid that comes in direct contact with their body forms what is called a boundary layer. This layer of fluid grips on tightly and interacts with the next layer of water, and so on, creating a frictional force that resists forward movement. What do swimmers do to reduce the drag created by skin resistance?

Streamline helps reduce impeding drag. Friction can also play a role.

Turbulence Drag Undisturbed water has a laminar flow, which is disrupted when a swimmer moves through it. As this occurs, a high-pressure zone develops in front of the swimmer where some of the water accumulates. In addition to this build-up at the front, some of the displaced water slips past the swimmer, crashing into the space the swimmer has just left and creating a low- pressure wake full of eddies behind the swimmer. As water flows from high- to low-pressure zones, the pressure differential causes a suction effect, which resists forward motion

Wave Resistance When a swimmer moves through the water, waves build up in front of them, creating a high-pressure swell that exerts a resistance. This wave is often referred to as a wall of water that acts to block the swimmer’s path.

Stroke technique

Why is stroke technique important Reduces resistive forces by using streamline position Kick increases propulsive force and enables body to maintain buoyant position on surface Maximise lift force with hand movement angled at 40 degrees Summation of arm movement increases the amount of force and velocity if stroke length and time is well executed. Increased velocity = increased momentum Greater impulse in the butterfly kick at the beginning of a race increases the linear momentum generated. Impulse is also present in the dive process to increase force production. Ultimately these principles will minimise the time taken for a rescuer to swim freestyle to reach a person in difficulty. This enables a fast and quick rescue of the person to ensure best possible outcome.