What Do I Really Need to Know About Biomechanics

The Cole’s Notes to Mr. Wardle’s abstract and somewhat disjointed

thinking (if you have had Mr Gajic as a teacher then you will be just fine)

Kinematics

• The branch of biomechanics that studies the movement with reference to the amount of time that it takes to carry out an activity

• It includes– Movement– Path of the Movement – and Time

Distance and Displacement

• Distance– The path that an object or body follows

• Displacement– The length of a straight line from start to finish

points

Speed and Velocity

• In this course the difference is not really needed for any practical applications as we are studying short distance linear movements

• Velocity is the change in position and the time it takes for it to happen

Acceleration

• Usually done as an average over a period of time

• The rate at which velocity changes• Can be easily found from D/T and V/T graphs• From Newton’s 2nd law (F=ma)

• Acceleration due to Gravity is 9.81m/s/s

Torque

• The moment of force at a perpendicular distance to a joint or point of rotation

• Ex - turning a bolt and the force on the handle (the further your hand is away from the blot the easier it is – the longer the moment arm)

• Ex – Closing a door (I think we have talked about this one enough)

Newton’s Laws

• 1st – Objects are Lazy

• 2nd – F=ma

• 3rd – Everything has an equal and opposite consequence

Linear Kinematics

• Momentum – mass X velocity

• Inertia – the reluctance of a body to change what it is doing

• Force – a pushing or pulling action that causes a change of state of movement of a body

Angular Kinematics• Movement but involving some sort of rotational

movement• Can happen with linear movement• Angular displacement is the number of degrees

(or radians, 1 radian = 57.3’) that an object moves through

• Angular velocity is the rate of change of angular displacement

• Angular acceleration is the rate of change of angular velocity

Examples of Angular Kinematics

• A skater turns at 360’ (6.28 radians) – this is her angular displacement (1 turn – it doesn’t matter how “big” she is – that would be circumference)

• If each turn takes her 1 second her angular velocity is 360’/s or 6.28r/s

• If she speeds up to double that rate in 1s her acceleration is 360’/s/s or 6.28r/s/s ending at 720’s

Angular Momentum

• Angular Momentum = Angular velocity X moment of inertia

• Is set once a body is “free” due to Law of Conservation of Motion

• Applies to skaters, divers etc– They decrease their moment of inertia (width –

bring their arms in) and in order to keep their Angular Momentum the same their Angular Velocity speeds up

D/T Graphs

• 1 – stopped (doesn’t matter where this is on the y axis)

• 2 – constant velocity• 3 - accleration

V/T

• Stopped

• Decreasing Velocity

• Increasing Velocity

• Stopped