# Pdhpe Yr11

Topics: Force, Classical mechanics, Buoyancy Pages: 2 (405 words) Published: June 24, 2013
Balance and Stability

Centre of Gravity
The centre of gravity of an object is the point at which all the weight is evenly distributed and about which the object is balanced. Knowing the position of the centre is very important to improve sports performance. The CG is constantly changing position: for example as we sit, run jump, eat and breath. The height of the CG is relative to the base of support. As object with low CG will tend to be more stable than one with a higher CG. THe CG need not lie within the physical limits of an objector person e.g. gymnastics and diving.

Line of Gravity
A straight line drawn from the CG to the ground is called the line of gravity. An object is most stable when the line of gravity fills the through the centre of the base of support.

Base of Support
The base of support of a body is the region bounded by the body parts in contact with a surface that is applying a reactive force against the applied force of the body (standing = foot)

Fluid Mechanics
Fluid mechanics refers to forces that operate in water and air environments. These forces affect how much well we move thought water or how we can move ourselves or projectiles through the air.

Flotation
To float is to maintain a stationary position on the surface of the water. If the buoyant force is greater than the weight force, the body will float. Buoyant force - is the upward force on an object produced by the fluid in which it is fully or partially.

Centre of buoyancy
The centre of buoyancy is at the centre of gravity of the water that the swimmer displaces fig 6.18.

Fluid Resistance
Forces act on us when we attempt to propel ourselves through a fluid environment. These include drag fore and lift force.

Drag
Sometimes refer to as resistance.
Is the force that opposes the forward motion of a body or object reducing its speed or velocity. The amount of drag depends on a variety of factors, these include. Fluid density, shape, surface, size of...