Biomechanics Part 2

4.3.9 State the relationship between angular momentum, moment of inertia

and angular velocity.

• Angular velocity –the measure of how fast an object is rotating; the change of angular displacement divided by the time taken.

• Torque (Moment) – turning force; will only work if force is applied so that it does not act through the axis.

• Moment of inertia – how difficult a body or object is to rotate about an axis.

• Angular momentum – the measure of the amount of rotation; an object that is spinning.

4.3.9 State the relationship between angular momentum, moment of inertia and angular

velocity. • Newton’s 1st law expressed angularly:– “A rotating body will continue to turn about its

axis with constant angular momentum unless an external unbalanced torque (moment is applied to it.” p. 102

• Law of Conservation of Momentum• When there is no external force (torque), no

change in angular momentum can occur.

4.3.10 Explain the concept of angular momentum in relation to sporting activities

• Gymnast doing a somersault in the air • Angular momentum comprises of moment of inertia multiplied by

angular velocity. Therefore during flight, if the moment of inertia is reduced, the angular velocity must increase to keep the angular momentum constant. This is why when a gymnast “tucks” during a somersault (by bringing her arms and legs towards the center of gravity and reducing the moment of inertia), she will rotate faster. Similarly, by the same principle, when a gymnast “opens out” prior to landing (increasing the moment of inertia), her rate of rotation will decrease.

• Activity 1 Parallel Uneven Bars article• Activity 2 Diver example• Work individually, in pairs or groups

4.3.11 Explain the factors that affect projectile motion at take-off or release

• Any object released into the air• Activity 3 – Outside ball throwing• Factors that affect projectile motion– Height of release– Speed of release– Spin– Angle of release– Gravity– Air resistance

4.3.12 Outline the Bernoulli principle with respect to projectile motion in sporting activities.

• The pressure exerted by a fluid is inversely related to its velocity

• Paper activity – p. 101– An increase in velocity, the pressure decreases– The paper moves up, from the higher pressure

below the paper towards the lower pressure above it.