Biomechanical Theory and Concepts Part 1 PDF

Lesson 11.1 THE NATURE OF FORCES AND NEWTON’S LAWS OF MOTION ~~~ TOPICS COVERED IN THIS LESSON...

Lesson 11.1 THE NATURE OF FORCES AND NEWTON’S LAWS OF MOTION ~~~ TOPICS COVERED IN THIS LESSON (a) Forces and Human Movement (b) Newton’s Three Laws of Motion © 2015 Thompson Educational Publishing, Inc. 1  Focussing Question ~~~ “What concepts and laws are fundamental to the study of biomechanics?” © 2015 Thompson Educational Publishing, Inc. 2  What Is Biomechanics? Biomechanics is the branch of kinesiology concerned with understanding the behaviour and function of the living human body when it is acted upon by forces. Simply put, biomechanics is the physics underlying physical movement and sport. Biomechanists play a key role in helping athletes and others develop proficient movement patterns— ones that minimize energy expenditure while facilitating performance. © 2015 Thompson Educational Publishing, Inc. 3  What Is a “Force”? A force is a push or a pull. Because forces have both magnitude (size) and direction, they are known as vector quantities. Force is measured in newtons (N). External forces are forces that originate outside the object or body that we wish to study (e.g., gravity, wind resistance, or surface friction). Internal forces arise within the system we are interested in studying—in this case, the human body (e.g., when a muscle contracts, it generates a force that results in the movement of the bone to which it is attached). © 2015 Thompson Educational Publishing, Inc. 4  Who Was Sir Isaac Newton? “To myself, I am only a child playing on the beach, while vast oceans of truth lie undiscovered before me.” Isaac Newton (1642-1727) Unquestionably, the most influential scientist of the 17th century, whose ideas became the basis for modern physics. Newton’s book “Philosophiæ Naturalis Principia Mathematica” (“Mathematical Principles of Natural Philosophy”), published in 1687, laid the foundations for classical mechanics. Mechanics is the parent discipline of biomechanics. © 2015 Thompson Educational Publishing, Inc. 5  Newton’s Accomplishments “I can calculate the motion of heavenly bodies, but not the madness of people.” —Isaac Newton, Physicist and Mathematician Newton was a key figure in the Scientific Revolution of the 17th century—one of the most influential scientists of all time. Newton made major contributions to the science of optics—he built the first reflecting telescope and developed a theory of colour. He shares credit with Gottfried Leibniz for the development of calculus. © 2015 Thompson Educational Publishing, Inc. 6  The Meaning of “Laws” in Science A scientific law is a generalized rule that describes a body of observations. Typically, scientific laws take the form of a mathematical statement—for example, Albert Einstein’s famous E = mc 2. Scientific laws imply a cause and effect and must always apply under the same conditions. Isaac Newton’s famous three laws of motion “capture the essence” of motion and allow it to be analyzed mathematically, over and over again, showing the same results. Newton’s laws are the foundation of the scientific field of mechanics (and, therefore, biomechanics). © 2015 Thompson Educational Publishing, Inc. 7  Newton’s Three Laws of Motion “If I have seen further it is by standing on the shoulders of giants.” —Isaac Newton, writing modestly of his accomplishments in a letter to his fellow scientist Robert Hooke in February, 1676. Newton’s three laws of motion together established the foundation for classical mechanics. The laws describe the relationship between an object or a body and the forces acting upon it, and its motion in response to these forces. © 2015 Thompson Educational Publishing, Inc. 8  1. The Law of Inertia “A body in motion tends to stay in motion and a body at rest tends to stay at rest unless acted upon by an external force.” Restated : A body or object either remains in a stationary position or continues to move at a constant velocity, unless an external force is exerted upon it. Inertia is the property of matter that causes an object to resist any changes in motion. © 2015 Thompson Educational Publishing, Inc. 9  2. The Law of Acceleration “A force applied to an object causes an acceleration of that object of a magnitude proportional to the force and in the direction of the force, but inversely proportional to the object’s mass.” In other words, F = ma Restated : Newton’s formula (F = ma) describes the relationship between the force acting on an object (F), its mass (m), and its acceleration (a). For example, as more mass is added to a blocking sled, a football lineman must generate more force for the sled to accelerate at the same rate. Proper technique and strength allow professional tennis players to apply more force when they hit the ball, causing the ball to accelerate faster. © 2015 Thompson Educational Publishing, Inc. 10  3. The Law of Action-Reaction “For every action, there is an equal and opposite reaction.” Restated : A reaction force arises whenever one body exerts a force on another. The reaction force is equal and opposite in magnitude and direction to the applied force. When a sprinter responds to the starter’s signal and pushes against the starting blocks, the blocks generate a reaction force that is equal and opposite in magnitude and direction to the force applied by the sprinter. Managing ground reaction forces can help a skier efficiently maintain control during a downhill run. © 2015 Thompson Educational Publishing, Inc. 11  Examples of the First Law of Motion The Law of Inertia A kettlebell resting on the floor is exerting a force on the floor and the floor, in turn, is exerting a force on the kettlebell. The floor exerts an equal and opposite force upward on the kettlebell. The kettlebell and the floor are in a state of equilibrium and no motion is observed. Whether an object is in a state of rest (the kettlebell) or in a state of motion (e.g., a curling rock), the object will remain in that state unless it is acted upon by an external force. © 2015 Thompson Educational Publishing, Inc. 12  Examples of the Second Law of Motion The Law of Acceleration (F = ma) Proper technique and strength allow professional athletes such as tennis players, golfers, and baseball players to apply more force when they swing their striking implements and hit the ball, thus causing the ball to accelerate faster. Suppose a basketball has four times more mass than a baseball. What happens if a force of 10 N is applied separately to each object? The acceleration of the basketball and the baseball will differ because the two objects differ in mass. Because the basketball has four times more mass than the baseball, its acceleration will be one- quarter that of the baseball. © 2015 Thompson Educational Publishing, Inc. 13  Examples of the Third Law of Motion The Law of Action-Reaction Newton’s third law of motion applies, for example, when a basketball player jumps to make a slam dunk. The action of pushing against the court floor leads to a reaction force—that is, the floor pushing back—and, ultimately, the athlete’s body leaves the ground. When a volleyball player bends her knees as she prepares to push against the floor and jump up to block a hit from an opposing player, the floor reacts or pushes back, and the player rises into the air. © 2015 Thompson Educational Publishing, Inc. 14  Revisiting the Question ~~~ “What concepts and laws are fundamental to the study of biomechanics?” © 2015 Thompson Educational Publishing, Inc. 15  Lesson 11.1 SUMMARY Biomechanics is the branch of kinesiology concerned with understanding the behaviour and function of the living human body when it is acted upon by forces. A force is a push or a pull. External forces are forces that originate outside the object or body that we wish to study. Internal forces arise within the system we are interested in studying. Newton’s three laws of motion together describe the relationship between an object and the forces acting upon it, and the effect of these forces. Newton’s three laws of motion are referred to as: (1)the Law of Inertia, (2) the Law of Acceleration, and (3) the Law of Action-Reaction. © 2015 Thompson Educational Publishing, Inc. 16  Lesson 11.2 LEVER SYSTEMS IN THE HUMAN BODY ~~~ TOPICS COVERED IN THIS LESSON (a) Types of Levers (b) Levers in the Human Body © 2015 Thompson Educational Publishing, Inc. 17  Focussing Question ~~~ “How do the three classes of lever in the human body function to produce movement?” © 2015 Thompson Educational Publishing, Inc. 18  The Earliest Study of Levers “Give me a place to stand and I will move the Earth.” Archimedes of Syracuse (c. 287 BC–c. 212 BC) The earliest writings regarding levers date from the 3rd century BC and were provided by Archimedes, the greatest scientist of his time. © 2015 Thompson Educational Publishing, Inc. 19  Who Was Archimedes? Archimedes was a Greek mathematician, physicist, engineer, inventor, and astronomer. Archimedes is regarded as one of the leading scientists in classical antiquity. In the minds of scientists and historians, Archimedes occupies the same renowned position in the history of science as Galileo, Issac Newton, Albert Einstein, and Marie Curie. Archimedes did not invent the lever, of course, but he did explain how levers work and how they provide a “mechanical advantage.” © 2015 Thompson Educational Publishing, Inc. 20  What Are Levers? Levers are simple machines. A machine is a device, consisting of fixed yet interrelated parts, that is capable of altering the direction and magnitude of a force. Levers perform one or more of the following functions: Balance two or more forces, Provide a force advantage, whereby less effort force is required to overcome a greater resistance force, or Provide an advantage in speed of movement, whereby the load to be moved moves farther and faster than the effort force. © 2015 Thompson Educational Publishing, Inc. 21  Levers in the Human Body The machine-like configurations of the bone- joint-muscle arrangements in our bodies are essentially levers. Knowledge of these arrangements can form the basis for developing musculoskeletal training and conditioning programs, as well as rehabilitative exercise regimens. Knowledge of these arrangements can also be used to re-design the physical world in which we live and work in order to make our movements safer and more efficient. © 2015 Thompson Educational Publishing, Inc. 22  Classifying Levers There are three classes of levers. These classes of levers are defined according to the relative positioning of the following components: The fulcrum or joint (the axis of rotation), The effort (point of application of the force), and The load (the mass of the object, body, or part being moved; also known as the resistance). © 2015 Thompson Educational Publishing, Inc. 23  Lever Configurations in the Human Body In the case of levers in the human body, the lever components consist of: The force applied through muscle contraction (the pull on the movable bone at the attachment site) is the “effort.” The joint where the bones come together is the axis or “fulcrum.” The mass to be moved by the muscle is the “load.” © 2015 Thompson Educational Publishing, Inc. 24  The Class 1 Lever A Class 1 lever is one in which the fulcrum (the axis of rotation) is located between the point of application of the force (the effort) and the resistance (the load) being moved. Everyday examples of first class levers include: See-saws Crowbars Pliers Scissors (two first-class levers joined together) A hammer pulling out a nail © 2015 Thompson Educational Publishing, Inc. 25  A Class 1 Lever in the Human Body An example of a Class 1 lever in the human body is the neck as it shifts from a position of flexion to a position of extension. The contraction of the trapezius muscle (effort) permits extension of the head (resistance). The spine is the fulcrum upon which the neck muscles lift the head. A Class 1 lever is the most versatile of all levers. It can afford a speed © 2015 Thompson and/or force Educational Publishing, Inc. 26 advantage.  The Class 2 Lever A Class 2 lever is one in which the resistance, (the load) is positioned between the point of application of the force (the effort) and the axis of rotation (the fulcrum). Everyday examples of second class levers include: Wheelbarrows Staplers Doors Can openers © 2015 Thompson Educational Publishing, Inc. 27  A Class 2 Lever in the Human Body An example of a Class 2 lever in the human body is the ankle joint (the fulcrum) in combination with contraction of the gastrocnemius muscle (the effort). This lever mechanism is capable of moving almost the entire weight of an individual (load) during plantarflexion (standing on one’s toes). A Class 2 lever affords a force advantage: a relatively small effort can lift © 2015 Thompson Educational Publishing, Inc. 28 a large load.  A Class 3 Lever A Class 3 lever is one in which the point of application of the force (the effort) is located between the fulcrum (the axis of rotation) and the resistance (the load). Everyday examples of third class levers include: Brooms Rakes Fishing rods Baseball bats © 2015 Thompson Educational Publishing, Inc. 29  A Class 3 Lever in the Human Body An example of a Class 3 lever in the human body is a person performing a biceps curl. The biceps muscle (effort) inserts on the radius (at the end of which is the load itself) in combination with the elbow joint (fulcrum). This is the most common type of lever found within the human body. A Class 3 lever provides a speed advantage, allowing relatively light resistance © loads to 2015 Thompson be moved Educational Publishing, Inc. through a 30 greater range of motion.  Revisiting the Question ~~~ “How do the three classes of lever in the human body function to produce movement?” © 2015 Thompson Educational Publishing, Inc. 31  Lesson 11.2 SUMMARY Levers are simple machines that provide a mechanical advantage. The bone-joint-muscle arrangements in our bodies are essentially levers. There are three classes of levers defined according to the relative positioning of the fulcrum (axis), the effort (force), and the load (resistance). Examples of levers in the human body are: Class 1 lever: the neck as it shifts from a position of flexion to a position of extension. Class 2 lever: the ankle in combination with contraction of the gastrocnemius muscle. Class 3 lever: the elbow joint when a person is performing a biceps curl. © 2015 Thompson Educational Publishing, Inc. 32