Biomechanics

Newton’s third law “for every action, there is an equal and opposite reaction” When we apply a force to an object, this is known as an action force. The object we apply a force to, applies a force back, a reaction force.

Revision of the three laws (ice hockey slap-shot) Group work- In groups identify at least 1 example of each law in the video clip. 1 st law- Inertia- Puck remains still until a force acts on it. Once puck is moving it will not stop until another force acts on it. 2 nd law- Acceleration- Force is applied to the puck to over come its inertia, which results in the puck accelerating. 3 rd law- Equal and opposite reaction- Puck hits goalie. Puck stops as goalie applies an equal and opposite reaction.

Momentum “Moving inertia” Dependent on both the body’s mass and its velocity Can be broken into two areas. Linear and angular momentum.

Linear Momentum Momentum will increase with either an increase in mass and/or velocity. This relationship is represented in the equation: Momentum = mass x velocity. Linear momentum is also direction specific. This is apparent in contact sports, like rugby, where a player’s momentum may force an opponent to move in the opposite direction. (video)

Angular Momentum When a mass rotates around an axis it has angular momentum (m x v x radius). Baseball bat- To move a mass at the end of a longer lever is harder than with a short lever. The key with baseball is to make contact on the ball with maximum momentum to overcome the inertia of the ball and to accelerate it in the opposite direction. Choke grip- Young children have less musculature development, therefore less strength. If we decrease the length of the lever they can increase the velocity of the bat and therefore increase the momentum.

Angular momentum (video)- Watch carefully during the video to see what the skater does to increase her spin rate (RPM) Experiment- Use the information from the video to either increase or decrease the spin rate on a computer chair. Conservation of angular momentum

Centre of Gravity The is a style used in the athletics event of. It was popularized and perfected by American athlete Dick, whose gold medal in the 1968 summer Olympics brought it to the world’s attention. Over the next few years the became the dominant style of the event and remains so today. Before, most elite jumpers used the Straddle technique, Western roll, Eastern cut-off or even the scissor-jump to clear the bar. (video) What relevance does this have in understanding the ‘centre of gravity’ concept? A body’s centre of gravity may coincide with its geometrical centre if it is symmetrical and the material make-up is consistent. In asymmetric bodies, with inconsistent material make-up, the centre of gravity may be some distance from the geometric centre, or even external to the body.

Conclusion Newton’s 3 laws of motion Momentum Centre of gravity