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Transcript
Biomechanics Chapter 15 Introduction We have now looked at factors that can influence our ability to perform at a high level. Chemicals we ingest, the equipment we use, and the training practices we choose Biomechanics will look at how physical forces affect performance. BIOMECHANICS How physical forces affect human performance. The application of the principles of physics to the analysis of movement. Biomechanics and careers Clinical practitioners of biomechanics examine physical causes and corrective actions to deal with serious physical injuries Other practitioners use biomechanical principles to design sport and office equipment that is safer, more productive/ efficient and more comfortable Prosthetic devices and orthopedic footwear Scientific models These include theories and laws These models reduce things to their essentials and assist scientists with understanding how things work in hopes of then using this knowledge to predict how they will behave and finally allowing them to influence and manipulate these things to improve performance Also creates a universal language and basis for communication. E.g.. Anatomical position Newton’s Model Sir Isaac Newton created this model in 1687. “The Three Laws of Motion” Explained how forces worked and became the basis for modern physics and thus biomechanics as well Law of Inertia Law of Acceleration Law of Reaction LAW OF INERTIA An object in motion remains in motion unless acted on by an external force. LAW OF INERTIA…more An object at rest remains at rest unless acted on by an external force. Law of Inertia States that a body will remain at rest or in a state of constant motion (equilibrium) unless acted upon by an external force. E.g. Human body ---remain standing unless external force is applied (muscle contraction, wind, someone else) Why does a Javelin eventually hit the ground? - Eternal forces acting on it (gravity, wind etc.) LAW OF ACCELERATION Force = mass X acceleration (F = ma) *Think* (15 = 3 x 5) Law of Acceleration F=ma Force equals the product of mass and acceleration A force applied to a body causes an acceleration of that body of a magnitude proportional to the applied force and in the direction of the applied force and inversely proportional to the body’s mass ***( Thus, a=F/m) Newtons Force is measured in Newtons (N) 1N = 1 (kg) (m) / (s2) Gravity is a pulling force which is exerted on us by the earth and it occurs at a rate of 9.8 m/s2 Thus, something that is 102 grams or 0.102 kg would have a weight of 1 N on earth. ( 0.102 x 9.8 = 1N) ***1000 grams = 1kg Weight vs. Mass Weight and Mass are not the same! On the moon a person would have the same mass as they do on earth but they would have less weight. Weight is affected by the force of Gravity and since there is more gravity on earth as compared to the moon you would weigh more on earth. Mass= amount of stuff (molecules etc. that make up an object). Mass is constant and unaffected by gravity. Types of motion Linear motion Movement in a particular direction Force acts through the centre of mass Angular Motion Movement around an axis The force does not act through the centre of mass. Rather it is off centre which results in rotation http://www.youtube.com/watch?v=MNDB5 QU5bBY 105 MPH ! Rotational/Angular Motion Slightly different than Linear motion - Instead of acceleration we have angular acceleration - Instead of Force we have a moment of force (torque) - Instead of mass we have a moment of inertia. Angular motion cont.. Just like Mass this is the resistance to rotation/movement. The larger the moment of inertia the larger the moment of force required to spin or stop spinning. In other words, the further the mass is from the axis, the greater the moment of inertia and thus the harder it is to start or stop spinning and vice versa. Rotation principles Figure skater pg 229. As the skater brings their arms into the centre of their body their angular acceleration increases because they have reduced their moment of inertia. Gymnastics---following a series of rapid somersaults in mid air the athlete straitens out their body. By opening up they increase their moment of inertia and slow down as they prepare to land. (i,e. the force stays the same and there is now a larger moment of force thus the body slows down Figure skating Law of Reaction When a body exerts a force on a second body the second body exerts a reactive force on the first body that is equal to the magnitude of the initial force but inn the opposite direction. Every action has an equal and opposite reaction As a person jumps up….there is a force exerted by the quadriceps on the ground and there is an equal and opposite force from the ground on the person which causes them to elevate. LAW OF REACTION Every action has an equal and opposite reaction. LAW OF REACTION…more Another example… TYPES OF FORCES Internal Forces – e.g. muscles pulling on bones. External Forces – e.g. gravity, contact with ground, environment (wind), sport equipment, opponent, etc. KINEMATICS vs. KINETICS Kinematics – Study of space and time aspects of movement, e.g. how far and how fast things travel. – Deals with time, displacement, velocity, and acceleration. – Deals with numbers. KINEMATICS vs. KINETICS Kinetics – What causes the motion? – Focuses on the various forces that are associated with motion. – The forces producing or resulting from the movement. – Descriptions of forces. Homework Read and make notes on Linear vs. Rotational motion Lever systems – What type of lever is working when you kick a soccer ball (knee) – When you perform a lateral arm raise with a 10 pound weight – Wheel barrow?