Fundamentals of Biomechanics IB SEHS- SL
Phases of Motion Preparatory - Execution - Follow Through Why is it important to break motion down into phases? So we can evaluate and correct in order to improve performance & prevent injury
Preparatory Phase • In a ready position • The movements that get the player ready for the force-producing movements
Execution Phase • performs the movements that produce force, impact or propulsion (kicking, hitting). • It is also at the point of contact or release of the movement
Follow Through • movement slows down after impact and the player prepares for the next action. • Important in slowing the body parts down over a longer period of time. • Absorbing the forces produced and helping to prevent injuries.
Basketball bounce pass video clip. • Basketball - Bounce Pass Preparation: • both hands on the ball • elbows in, wrist cocked, fingers spread (use finger pads)
Execution: • step forward with one foot • extend arms and snap wrists • bounce ball on floor approximately 2/3 of the distance between you and target (bounce pass)
Follow-Through: • finish with arms extended and palms facing out and thumbs pointing down
Observe the differences in the two swings. • Video Clip. Cricket vs Baseball (6 min) • Additional question • Which sport is it harder to hit the ball? clip of pitching phases of motion (5min)
What is a lever? Rigid structures hinged at one point (fulcrum) to which forces are applied to two other points (effort and load)
Resistance arm- distance between load & fulcrum Effort arm- distance between effort & fulcrum
What parts of the body are used to create a lever? Fulcrum Effort Load Joints Muscles Resistance, gravity, weight
Levers 1. First Class Lever: The fulcrum lies between the effort and load.
2. Second Class Lever: the fulcrum lies at one end with the effort at the other and the load in the middle. Ex. Standing heel raise Levers mechanical advantage is greater than 1, which means larger loads can be moved with less effort.
3. Third Class Levers: the effort lies between the load and the fulcrum. Levers Mechanical advantage is less than 1, which means more effort to move smaller loads.
Human body and Levers Biceps flexion & triceps extension are antagonistic muscle actions. Each can work as a lever. What type of levers are acting on each side of the humerus? Draw a picture of each lever.
Human body and Levers What type of lever is at the neck when you flex and extend?
Human body and Levers What type of lever is at the toes joints when you go up on your toes?
Types of Levers Levers
Long leversresult in greater speed at the end of a limb. This in beneficial for throwing or striking an object. Short lever can be moved with less force and at a greater speed. This is beneficial for moving body parts quickly and applying strength for pushing, pulling and lifting. How can the length of a limb change the how a lever functions?
In the human body, levers are made of joints (fulcrum) and the bones that connect them to the objects being moved. Levers in the human body can be manipulated to improve speed & apply large forces at the same time Can you think of any situation in the human body where this occurs? (hint: think about changing the length of a limb) . Running – lifting your foot and knee will create a shorter lever arm and increase speed. Boxing- flexing elbow creates a shorter lever arm and increase speed of a punch.
Compare the throwing of a ball by hand and with the throwing of a ball with a jai alai basket, lax stick… Which is faster? About 95-100mph About 170mph Fastest shot 111mph lacrosse shot clip Lincecum clip Jai Alai clip
How can a 5’10” pitcher be such a powerful pitcher? An excessively large stride increases the speed the arm can move as a 3rd class lever. See picture on next page. The normal stride length for a pitcher is 77% to 87% of his height. Lincecum's stride is 129%, some 7 1/2 feet
Load Effort Fulcrum
Biomechanics: the application of mechanics to the human body and sporting implements 1. Kinematics: study of motion. a. linear- straight line b. curvilinear- curve (shot put) c. angular- motion around an axis (rotational- spinning) d. general- linear & angular Examples velocity, acceleration, displacement, distance.
General Motion Most common type of motion Angular motion- synovial joints segments rotating around each other Linear Motion
Measuring Movement Scalars are quantities that are fully described by a magnitude (or numerical value) alone. Vectorsare quantities that are fully described by both a magnitude and a direction. Vectors video clip Scalars & Vectors tutorial
Position • Distance: is a scalar quantity that refers to "how much ground an object has covered" during its motion. • Displacement: is a vector quantity that refers to "how far out of place an object is"; it is the object's overall change in position. distance & displacement tutorial
Speed: is a scalar quantity that refers to "how fast an object is moving.” Speed can be thought of as the rate at which an object covers distance. Speed =distance / time
Velocity: is a vector quantity that refers to "the rate at which an object changes its position." Velocity tutorial
Velocity – Time Graphs a positive velocity means the object is moving in the positive direction a negative velocity means the object is moving in the negative direction.
Velocity – Time Graphs the slope of the line on a velocity-time graph reveals useful information about the acceleration of the object.
Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity. An object is accelerating if it is changing its velocity. Acceleration tutorial
Velocity – Time Graphs constant positive velocity, no acceleration constant negative velocity, no acceleration positive velocity, positive acceleration positive velocity, negative acceleration negative velocity, negative acceleration negative velocity, positive acceleration Putting it all together. Watch the last clip and pay attention to the objects movement & when the line crosses the X-axis Review & Quiz
2. Kinetics Forces involved in the movement of an object or body. (angular & linear) Linear: force, gravity, mass, laws of motion, momentum, impulse.: Angular: torque (moment), Levers, center of mass.
Force vectors a pushing or pulling action that causes a change of state (rest/motion) of a body. Measured in units called Newtons (N). Rugby vs Football clip 8 min
Typesof Forces: Frictional (air, fluid): force that slows an object down, usually in the opposite direction Tensional: force through a string, rope…when pulled from opposite ends Normal: support force that is exerted on an object when in contact with a stable object
Typesof Forces: Applied: force that is placed on an object by someone/thing. Gravitational: (also known as the weight of an object) force pulling objects to Earth. Technically the mutual force of attraction between all objects.
Forces can produce three types of motion: Translation: change in position Rotation: circular movement of an object around a center of rotation. Deformation: change in shape/size of an object due to an applied force or a temperature change.
Newton’s Laws of Motion in Sport First Law (Law of Inertia) • An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. First Law video clip BMX inertia First Law Tutorial
Second LawThe acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. Newton’s Laws of Motion in Sport Arrows represent the magnitude (size) of the force Sports sceince -force clip 6 min Second Law tutorial Second Law in Sports
Momentum is a vector quantity that can be defined as "mass in motion." Momentum (p) = mass • velocity Momentum (angular and linear) 2 min Momentum tutorial
Impulsechange in momentum. A force produces an acceleration, and the greater the force acting on an object, the greater its change in velocity and, hence, the greater its change in momentum Bat swing video
Impulse – Momentum Relationship Baseball and Impulse/ Momentum video clip momentum (p)= mass • velocity Force x time =mass x velocity Bat *Ball *Mass will remain constant
Force – Time Graphs Explain the graph to the right using the picture to the left? The force increases until the ball reaches a point of max compression. The ball comes in contact with the racket, compresses, decompresses & then contact ends. Note the time of contact : 40ms (.04 sec)
Third LawFor every action there is an equal and opposite reaction. (every force involves the interaction of two objects) Newton’s Laws of Motion in Sport Third Law in Sports clip Third Law tutorial
the point at which the body is balanced in all directions. Center of mass a change in body position can change the position of the center of mass within or outside the body. The center of mass is the point at which the mass of an object is concentrated. Center of mass tutorial
A lineman crouches low so that his center of mass is closer to the ground. This makes it hard for an opposing player to move him. Center of mass Which is a better location to tackle and why? tackling a runner low -- far from the center of mass -- it takes less force to tackle him than if he were tackled high. Football tackle below center of gravity
Center of mass Why does a lineman stay low to the ground, especially inside the red zone? A lineman crouches low so that his center of mass is closer to the ground. This makes it hard for an opposing player to move him.
The Fosbury Flop! Center of mass *notice how the center of gravity is located outside the jumper’s body. Western Roll Straddle Jump Physics behind the jump Fosbury Flop