Mechanics and Motion AS 2562

Learning Objectives At the end of this section you should be able to: Describe the difference between linear, angular and general motion. Understand the effect and application of force on sporting techniques. Apply 3 of Newton’s Laws of Motion to sporting examples. Describe the mechanical principles around stability and why some activities need more than others. Apply this knowledge to analysis and improvement of sporting techniques.

Types of Motion There are three main categories: LinearAngular Linear Motion is when all of a body moves in a line (straight or curved) with all parts moving in the same direction. Angular Motion is when a body or part of it moves in a circle (or part of) about a point called the axis of rotation. General Motion is a combination of linear and angular motion. Task: Give an example of each of the three types of motion. General Motion (bola)

Forces A Force is: ‘A push or pull that alters, or tends to alter, the state of motion of a body. It could cause body to move from rest, change direction, accelerate, decelerate or change shape. The size and direction of the force will effect the motion. Task:List three examples, from your sports, where force is used and explain the effect of the force on movement.

Newton’s Law of Motion Without force there can be no motion. Newton’s Three Laws look at this in more detail. Newton’s First Law ‘A body continues in a state of rest or uniform velocity unless acted upon by an external force’. Newton’s Second Law ‘When a force acts upon an object the rate of change of momentum experienced by the object is proportional to the size and direction of the force’. Newton’s Third Law ‘For every action there is an equal and opposite reaction’. Task:Give an example of each of the three laws in action in the activity from your PPP.

Centre of Mass The ‘mass’ of a body is the amount of material with which it is made. The ‘centre of mass’ of a body is where the mass is considered to be concentrated. It is the point at which it is balanced in all directions. In uniform objects (symmetrical) it is the geometric centre. (1/2 the mass above, below, left and right, front and back etc.) However, it can in non-uniform shapes lie outside the actual body. In the human form the centre of mass has no fixed point but is dependent on the position of the performer at any given time.

Centre of Mass Due to the body composition the centre of mass of all athletes varies, as bone, fat, tissue and muscle all contribute to total mass and are in different proportions in each performer. The range of body positions also contributes to the centre of mass. Athletes standing still in a ‘normal position have one centre of mass (lower for women than men) but this can be altered by the raising of the arms or straddling of the legs. It is also dependent on other factors such as balls, weights, opponents etc.. In some body shapes (high jumper, trampolinist, gymnast) the centre of mass can be outside the body. Task: Draw and label the centre of mass of a performer in 3 different positions in you PPP activity.

Stability If a body is ‘stable’ it is difficult to move from it’s balanced position. If it is easy to move something from balanced to unbalanced it is not stable. This has benefits and implications for performers, both in a positive and negative way. Task:Stand, sit and lie in various positions and get partener to try and move you and note which one feels most stable to least stable and identify key common features of the more and less stable positions. It is dependent on these main principles: oPosition of the centre of mass oBase of support oPerformers line of gravity oMass of the performer

Stability Centre of Mass Line of Gravity 1.This is a stable position because…. 2.It would become less stable by…… Base of Support

Centre of Mass and Application of Force The direction of the force being applied, in relation to the centre of mass, will dictate if the motion is linear or angular. If the line of the force is through the centre of mass the resulting motion will be linear. This is called a direct force. If the line of force passes outside the centre of mass the motion will be angular. This is called an eccentric force.

Centre of Mass and Application of Force Force applied through centre of mass – direct force. Ball goes up but with no spin – linear motion. Force applied to side of ball – eccentric force. Ball spins – angular motion. Liner MotionAngular Motion The more spin needed the greater the force and the further away from the centre of mass it needs to be applied.

Learning Check Can you: Describe the difference between linear, angular and general motion. Understand the effect and application of force on sporting techniques. Apply 3 of Newton’s Laws of Motion to sporting examples. Describe the mechanical principles around stability and why some activities need more than others. Apply this knowledge to analysis and improvement of sporting techniques. Explain why a handstand is more difficult than a headstand.