Centre of Mass & Stability.pptx
Transcript
Centre of Mass & Stability Biomechanics Centre of mass defined Centre of mass is the point at which all weight is evenly distributed. Locating the centre of mass The CoM is not a tangible or fixed point. Therefore, it is not always connected to body in question. Locating the centre of mass Generally...
Centre of Mass & Stability Biomechanics Centre of mass defined Centre of mass is the point at which all weight is evenly distributed. Locating the centre of mass The CoM is not a tangible or fixed point. Therefore, it is not always connected to body in question. Locating the centre of mass Generally speaking, the location of the centre of mass for a human in the anatomical position is around the navel. Women generally have a slightly lower CoM. However, as PE students, we must be aware that as the body position changes, so does the CoM. Locating the centre of mass As the weight lifter lifts the weight above his head, the weight distribution has now changed in comparison to the anatomical position. As there is now a substantial increase in weight above the head, the centre of mass moves upwards. Locating the centre of mass As the performers body position changes, so does his CoM location. Due to the performer moving significant amounts of mass forward (legs, arms and upper body), the CoM also moves forward. In this case, the CoM has moved outside the body. Terminology: Line of gravity The line of gravity runs from the centre of mass vertically down to the ground Terminology: Base of support (BoS) & points of contact (PoC) Points of contact are the number of body parts that are in contact with the surface area. The base of support is the area covered between the points of contact. Low stability Narrow BoS Wide BoS 2 PoC High stability 1 PoC Principle of balance: If your line of gravity falls within your base of support, stability is increased. Principle of balance: The more points of contact, the greater the balance. You will see that the tackler is coached to put his hands behind his opponents knees. This will allow the tackler to squeeze and lift the opponents front leg off the ground. Once this is achieved, the opponent will only have 1 point of contact and a narrow base of support. As a result, he will lack stability and balance. 2 PoC Principle of balance: the greater the area of support the greater the balance Narrowe r BoS Wide BoS In this case, the tackler has a wider base of support than that of his opponent. As a result he has a further competitive advantage in this contest. Principle of balance: The lower the centre of mass, the greater the stability. The tackler has gained a further advantage as his CoM is lower to the ground than his opponent. When coaching, you encourage the tackler to get “eyes to thighs”. This assists the performer to get his body lower to the ground than his opponent. Principle of balance: the greater the mass, the greater the stability. Lower mass High mass Although not essential in rugby, a performer’s mass can go someway to determine the outcome of a tackle. The greater the mass, the more resistant the performer is to external forces being applied. Likewise, the greater the mass of the tackler, the more force he is able to apply to the opposing force (the opponent being tackled). Apply it! Exam question: Compare the balance and stability of a gymnast performing a headstand in comparison to a handstand. Explain your reasoning. (4m)
