Introduction to Bio Mechanics

8/6/2019 Introduction to Bio Mechanics

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What do these two men have in

common?

� Sir Isaac Newton Leonardo Da Vinci



H istory of Biomechanics� In the fifteenth century, Leonardo da Vinci wrote:� ´Mechanical science is the noblest and above all

other, the most useful, seeing that by means of it,

all animated bodies which have movement performall their actionsµ (cited in Cross and Lyle, 2006 pg 130)

� However it was not until 1687 that Isaac Newtonpublished Principia, that a full and correct

understanding of the laws of motion was gained.� Superseeded by Hesienberg and Einstein, Newton·s

laws still provides the fundamental relationshipsbetween forces and motion during everyday life.



Newton·s three laws of motion

� S traight line ² CONSTANT SPEED UNLESS ACT ED ON BY A FORCE

�

Variation of force ² FORCE =MASS

X ACCELER AT ION



TH E FIRST LAW OF MOT ION

� T he first law states that:� Every body continues in its state of rest, or of

uniform motion in a right (straight) line unless it is

compelled to change that state by forces impressedupon it� For example a ball will stay at rest until hit or

kicked, and will keep moving in a straight line

unless a force (gravity, air resistance or lift) actsupon it to curve the flight.� Also known as ¶Galileo·s law·



TH E SECOND LAW OF MOT ION

� T he second law of motion states that:� T he change of motion is proportional to the motive

force impressed, and is made in the direction of the

right (straight) line in which that force is impressed� Often translated as force = mass x acceleration� For example a tennis player wishing to hit a faster

serve must apply greater forces than required to hit aslow serve� T he force must also be in the correct direction



TH E TH IR D LAW OF MOT ION

� T he third law of motion states that:� For every action there is always opposed an equal

reaction; or, the mutual actions of two bodies upon

each other are always equal, and directed tocontrary parts� Must be two bodies involved, although not always

in contact, forces on the bodies must be opposite

in direction, but equal in size and occur at the same time� Small rugby player in a collision with a larger one

will experience the same force although in the

opposite direction



Why is this relevant to Sport?

� T he science of biomechanics is theapplication of these mechanics to the humanbody and the result of these forces.

� Remember that forces are measured inNewtons.



Activity

1. Define the terms force, mass, velocity and acceleration andgive the unit of measurement for each.

2. S tate Newton·s First Law of Motion.3. An ice hockey puck is struck by a player and travels across

the ice to rebound from the far wall of the rink. Assuming that both the friction between puck and ice and the airresistance are negligible and that the puck travels from right to left as you look at it, sketch force diagrams to show whatforces act in each of the following situations.

a) While the puck is stationary before being struck.b) While the stick is in contact with the puck.c) While the puck is travelling across the ice before it hits the

wall.d) While the puck is in contact with the wall.







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Introduction to Bio Mechanics