1. Quick Questions How do you calculate acceleration?
Draw a speed-time graph for constant speed
Draw a distance-time graph for deceleration
Calculate the speed and velocity for a 400m runner who completes the race in 1min 20 seconds
Describe Newton’s 1st Law of motion

2. Biomechanical Principles - Angular Motion
Biomechanics
Biomechanical Principles - Angular Motion

3. Most: Apply your knowledge to a variety of sporting examples
Learning Objectives
Learning Objective:
Understand angular motion is produced, what affects it and calculate quantities of angular motion.
Learning Outcomes:
All: Describe how angular motion is produced, what affects it and calculate quantities.
Most: Apply your knowledge to a variety of sporting examples
Some: Interpret graphs and Explain how athletes can use their knowledge to maximise performance

4. Key Terms Angular motion Eccentric force Axes of rotation
Longitudinal
Frontal
Transverse
Moment of inertia
Angular velocity
Angular momentum
Mass of body
Distribution of mass from axis of rotation
Radian

5. Key Terms Angular Motion – movement around a point
Eccentric Force – a force applied at a distance away from an axis of rotation, causing a rotational moment 
Axis of rotation = an imaginary line or point about which the body or part of the body rotates.
longitudinal axis– runs top to bottom passing through the centre of mass (pirouette)
transverse axis– runs left to right passing through the centre of mass (somersault)
frontal axis– runs front to back passing through the centre of mass (cartwheel)
Moment of Inertia - a quantity expressing a body's tendency to resist angular acceleration, It’s the sum of the products of the mass of the body with the square of its distance from the axis of rotation.
Angular Momentum - the quantity of rotation of a body, It’s the product of its moment of inertia and its angular velocity.
Mass of Body – how big it is
Distribution of mass from axis of rotation - how far away the body is spread from the point it’s turning about.
Radian – a measurement for angular motion. 1 rad = about 57.3 degrees 2𝜋 rad = 360 degrees

6. What is Angular Motion? Movement around a point E.g. a somersault
E.g a pirouette
E.g. a knee joint when cycling
E.g. an ankle joint when running

7. How is angular motion created?
A force is applied outside the centre of mass This is known as an eccentric force

8. What affects angular momentum?
Angular momentum is measured by:
Moment of inertia x angular velocity
Moment of inertia is affected by your
Mass (size) – small person = lower moment of inertia
Distribution of mass from axis of rotation (how spread out your body is – tucked in a ball = lower moment of inertia
Angular velocity is affect by
Distance
Time
The smaller your body (less mass) and more you are tucked (closer distribution of mass to axis of rotation) the lower your moment of inertia, therefore the less power you need to rotate, so you can rotate faster v(higher angular velocity)

9. Angular momentum Moment of inertia x angular velocity
Man 90kg, r = 75cm – moment of inertia = 67.5kgm²
- angular velocity =3rad/s
therefore angular momentum = kgm²rad/s
Woman 70kg, 0.6m – moment of inertia = 42kgm²
- angular velocity = 5 rad/s
therefore angular momentum = 210 kgm²rad/s
It would be harder to stop the smaller woman because she has a higher velocity & therefore higher angular momentum. However if a man could go faster he’d have more angular momentum so would be harder to stop)
(Moment of inertia = mass x radius²)

10. Exam Questions
Jan a) identify the three main axes of rotation and give a sporting example of each. (3)
June c) Explain the factors that affect the moment of inertia of a performer. Describe how a sprinter uses this concept to improve the efficiency of the recovery phase of the stride action. (6)
Jan a) A gymnast performs a somersault rotating through 6 radians in 0.5 seconds. Identify the axis of rotation through which the gymnast turns and calculate the average angular velocity of the somersault. (3)
June c) Describe the analogue of Newton’s First Law of Motion. Explain how a figure skater controls angular velocity when performing a multiple spin about the longitudinal axis. (6)
June d) Using practical examples, describe the use of the three axes of rotation in sport. Explain how rotation is initiated by a performer.
Describe the angular analogue of Newton’s First Law of Motion and use it to explain how a high board diver performing somersaults uses their body position to maximise performance during the following phases of the dive.
- Take off from the diving board
- During flight
- Just before entry into the water. (20)
June d) What is meant by the terms Angular Velocity, Moment of Inertia and Angular Momentum and sketch a graph showing their relationship when a gymnast performs a somersault from take-off to landing. Compare a gymnast’s use of the analogue of Newton’s First Law of Motion to control the performance of a somersault with that of a skier performing a turn during slalom. (20)