Essay Question 2:

Refer to the following diagram

Using the following sub headings, describe the key biomechanical principles involved in a baseball pitcher throwing a curve ball from right to left.

a) Segmental Interaction (7 marks)

Body parts move in a sequence to generate the largest force or accelerate possible.
To sequentially produce a maximal force effectively, the following principles need to be applied:
1. The stronger and larger muscles of the thighs and trunk are moved first followed by the smaller and faster muscles. This is seen in diagram 1.
2. Sequentially accelerate each body part so that optimum momentum passes from one body part to the next. In the transition from diagram 1 to 2, we see this sequential acceleration of muscle movement.
3. Each body part should be stable so that the next body part accelerates around a stable base to transfer momentum. In pitching it is essential to adopt a wide stance to increase stability. This is done by placing legs further apart from each other.
4. Use as many body parts as possible, so force can be applies over the maximal possible time. The pitcher can increase number of segments by getting side on, whilst also uncocking wrist prior to throw.
5. Follow through is important to prevent deceleration of last segment and safe dissipation of force. This can be seen in the transition from diagram 3 to 4.
6. Ensure all forces are directed towards the batter (the target)

b) Spin (6 marks)
1. As the pitcher is throwing a curveball, the type of spin is sidespin.
2. Diagram

3. At the commencement of the throw, an eccentric force is applied to the ball to cause the object to spin. This is an off centre force applied to produce angular motion.
4. Bernoulli’s principle states that velocity is inversely proportional to pressure.
5. The Magnus effect is the term used to describe the effect of rotation of an objects path as it moves through a fluid.
6. An area of high pressure and low velocity air is created on the right side of the ball, whilst, and area of low pressure high velocity air is created on the left side of the ball. As a result air moves from an area of high pressure to an area of low pressure and the ball curves form right to left.

c) Inertia / Moment of Inertia (3 marks)

- Moment of Inertia is referred to as the distribution of mass and axis of rotation.
- Inertia is the term used to describe the amount of resistance to a change in an objects state of motion. The greater the inertia, the greater the force required to move.
- If the body mass is close to the axis of rotation, rotation is easier to manipulate. This makes the moment of inertia smaller and results in an increase in angular velocity.
- To reduce the balls moment of inertia, the pitcher bends his arms at the elbow bringing the mass of the ball closer to the axis of rotation, seen in diagram 1. This allows the pitcher to generate greater angular velocity at the arm which is then transferred into the ball at the point of release seen in diagram 3.

d) Impulse (4 marks)

Impulse refers to the change in momentum of an object. It is calculated in the equation: Impulse = Force x Time. Therefore the longer the force is applied to an object and the greater the size of the force applied, the greater the objects impulse.

In the case of a pitcher, it is important for the pitcher to generate a large impulse. He can do this by either increasing, the force applied or increasing the time the force is applied.

Increasing Force: In order to increase the application of force through the pitch, the pitcher should attempt to maximise number of segments use, adopt a side on position and ensure to follow through in order to produce optimum segmental interaction.

Increasing Time: In order to increase the time component, the pitcher should attempt to maximise the number of body segments used in the throw and adopt a side-on position to ensure force is applied over a longer period of time. By utilizing a follow through, time can also be maximized whilst also preventing deceleration of the last body segment.
This can be shown diagrammatically: