Principles of Biomechanical AnalysisPSE4UMr. MacMillan

Review of Biomechanics The Laws of Motion

1st – Law of Inertia 2nd – Law of Acceleration 3rd – Law of Reaction

Types of Motion Linear

Movement in a particular direction Sprinter accelerating down a track

Rotational Movement about an axis What are the three axis’?

Longitudinal, anterio-posterior, horizontal Ice skater spinning or a gymnastic

somersault

Linear Motion Acceleration in a straight line Force as a vector

Force as a pull or push of a certain magnitude in a certain direction

Rotational Motion Is comparable to linear motion but the

object spins around an axis Acceleration is angular Torque is measured rather than force Moment of inertia

Resistance to rotation Larger the moment of inertia, the

larger the moment of force needed to maintain the same angular acceleration

Linear and Rotational MotionLinear Motion Rotational Motion

Displacement Angular Displacement

Velocity Angular Velocity

Acceleration Angular Acceleration

Force Moment of Force (torque)

Mass Moment of Inertia

Ice Skating

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The ice-skater begins to spin with arms spread apart then suddenly brings them closer to the body. The end result of tightening up is that the skater’s spin (angular velocity) increases, seemingly miraculously

Gymnastics

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Following a series of rapid somersaults in a tight position, the gymnast does a forward flip with the body positioned more or less straight. By opening up, the gymnast increases the moment of inertia, thereby resulting in a decrease in angular velocity

Diving

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After leaving the high diving board, the diver curls tightly and then opens up just before entering the water. By opening up before entry, the diver increases the moment of inertia, thereby slowing down the angular velocity and hopefully ensuring a smooth and safe entry.

The Lever Systems Class I Lever Class II Lever Class III Lever

The fulcrum (axis) is located between the force (effort) and the resistance (load)

Class I Lever (e.g. teeter-totter)

The resistance is between the fulcrum and the resistance

Class II Lever(e.g. wheelbarrow)

The force is between the fulcrum and the resistance

Class III Lever(e.g. snow shovel)

Seven Principles of Biomechanical Analysis

1. Stability2. Maximum force3. Maximum velocity4. Impulse5. Reaction6. Torque7. Angular momentum

Principle 1: The lower the centre of

mass, the larger the base of support, the closer the centre of mass to the base of support and the greater the mass, the more stability increases.

Principle 2: The production of maximum force

requires the use of all possible joint movements that contribute to the task’s objective

Principle 3: The production of maximum velocity

requires the use of joints in order – from largest to smallest

Principle 4: The greater the applied impulse, the

greater the increase in velocity

Principle 5: Movement usually occurs in the

direction opposite that of the applied force

Principle 6: Angular motion is produced by

application of force acting at some distance from an axis, that is, by torque

Principle 7: Angular momentum is constant when an

athlete or object is free in the air.

Free Body Diagrams Free body diagrams, are a tool for solving problems with

multiple forces acting on a single body. The purpose of a free body diagram is to reduce the

complexity of situation for easy analysis. The diagram is used as a starting point to develop a mathematical model of the forces acting on an object.

Below is a picture of a flying jet.

Force = m a M = mass A = acceleration

Acceleration = (v – u) / t

V = final velocity U = starting velocity T = time

Momentum = m v M = mass V = velocity

Impulse (N/s) = Ft = m Δv

M = mass Δ v = average velocity

Change in Momentum = m (V2 – v1)

M = mass V2 = final velocity V1 = initial velocity

Biomechanical Formulae

Your Task! Read pages 230 – 234 Answer Questions on Handout on course

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