Biomechanics - Laws of Motion

BIOMECHANICALPRINCIPLESPHYSICAL FORCES AND HUMAN PERFORMANCE

Biomechanics Examines the internal and external forces acting on the human body and the effects produced by these forces Aids in technique analysis and the development of innovative equipment designs Draws on knowledge from sports medicine, physical therapy, kinesiology, and biomechanical engineering

SIR ISAACNEWTON Scientific models reduce things to their essentials Establish a basis for understanding how things work Predict how they will behave influence them to behave in ways we want Sir Isaac Newton’s “model” explained the workings of physical forces in the universe and laid the basis for modern physics

Equilibrium andConservation of Energy Newtons’s theory rests on two assumptions: Physical Equilibrium and Conservation of Energy Equilibrium: “perfect” situation - more than one force acts on a body, sum of forces = 0, no change in Velocity COE - energy cannot be created or destroyed but can only be converted form one form to another.

NEWTON’S “MODEL UNIVERSE”THE LAWS OF MOTION• THE LAW OF INERTIA• THE LAW OF ACCELERATION•THE LAW OF REACTION

The Law of Inertia Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. Newton’s First Law asserts that a body will remain at rest or in a state of constant velocity unless acted upon by an external force. Examples of forces?



THE LAW OF INERTIA

The Law of Acceleration The relationship between an objects mass (m), its acceleration (a), and the applied force (F) is F=ma F is measured in Newtons (N) (kg.m/sec2). So a one-newton force can change the acceleration of a 1 kg mass by 1 m/sec2. Force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body’s mass could be applied to projectiles, such as javelin or a baseball where you can calculate acceleration by measuring change in speeds.

Terms to understand… SPEED: how fast an object is moving - S = D/T VELOCITY: the rate at which an object changes its position. V = D/T (with direction) Velocity is a vector quantity. As such, velocity is direction aware. ACCELERATION: rate at which the velocity of an object changes over time

CALCULATING ACCELERATION

CALCULATING ACCELERATION

CALCULATING ACCELERATION

Impulse and Momentum Momentum: The tendency for a moving object to keep moving. Product of Mass and Velocity P = mv Impulse: The change in momentum P

The Law of ReactionFor every action there is anequal and oppositereaction.When a body exerts a forceon a second body, thesecond body exerts areactive force on the firstbody that is equal inmagnitude and oppositedirection.

LEBRON AND NEWTON’S 3RD LAW

Newton’s 3rd Law

Weight vs. Mass As long as you stay on Earth, the difference is more philosophical than practical. MASS is a measurement of how much matter is in an object WEIGHT is a measurement of how hard gravity is pulling on that object “centre of gravity” is a misnomer, should be “centre of mass”