-Many forces act to oppose objects in motion. These include air and water resistance and friction.
Year 11 biomechanics with levers, force summation
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Biomechanics The study of forces and their effects on the human body Year 11 Achievement Standard 1.2
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Characteristics of motion <ul><li>Linear motion </li></ul><ul><li>Motion that occurs is a straight line. All parts of the body move in the same direction and at the same speed (e.g. jumping up in the air to catch a ball or travelling in a car). </li></ul>Line out jumper in Rugby Union Drag Racing
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Characteristics of motion <ul><li>Angular motion </li></ul><ul><li>Motion that occurs around an axis. This axis can be internal (e.g. body parts rotating around a joint) or external (e.g. spinning a ball on your finger). </li></ul>Spinning a ball on your finger Spinning figure skater
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Characteristics of motion <ul><li>General Motion </li></ul><ul><li>A combination of linear and angular motion. This is the most common of all movements, as most human movement requires the rotation of body parts around joints (e.g. cycling, swimming and running). </li></ul>
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Characteristics of motion <ul><li>Apply your knowledge! </li></ul><ul><li>Classify the following physical activities as linear motion or angular motion or general motion. </li></ul><ul><li>Sprinting </li></ul><ul><li>Rebounding a basketball </li></ul><ul><li>Driving a car </li></ul><ul><li>Tossing a underhand ball in basketball </li></ul><ul><li>Horse riding </li></ul><ul><li>Lawn bowls </li></ul>
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Centre of gravity <ul><li>Centre of gravity can be defined as “the single point at which all parts of an object are equally balanced”. </li></ul><ul><li>For a ‘normal’ human being standing upright, their centre of gravity lies around the area of their navel. </li></ul><ul><li>A persons centre of gravity can change depending on their body position because as mentioned before, the centre of gravity is the exact point where all parts of an object are equally balanced. </li></ul><ul><li>The centre of gravity can also lie outside an object , especially if the object is bent over or leaning in a certain direction </li></ul>
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Centre of gravity = Centre of gravity Centre of gravity for a “normal person”
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Centre of gravity <ul><li>Centre of gravity for a person whose hands a stretched in the air </li></ul>= Centre of gravity
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Centre of gravity <ul><li>Centre of gravity outside of a persons body </li></ul>= Centre of gravity
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Line of gravity - The line of gravity is important when determining the stability of an object. <ul><li>Line of gravity is the vertical line that passes through the centre of gravity to the ground. </li></ul><ul><li>If the line of gravity falls within the object’s base of support (i.e. its contact with the ground), the object is relatively stable. </li></ul><ul><li>If the line of gravity falls outside the object’s base of support (i.e. its contact with the ground), the object is relatively unstable. </li></ul>
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Line of gravity Centre of gravity STABLE Centre of gravity UNSTABLE Line of gravity Line of gravity
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Base of support – The object on the left is more stable because of its relatively larger BOS <ul><li>BOS is the area within an objects point of contact with the ground. The larger the area the base of support covers, the more stable an object will be. </li></ul>Wide BOS Narrow BOS BOS BOS
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Line of gravity, BOS in relation to movement <ul><li>The line of gravity (LOG) must go outside the base of support to initiate or continue movement. </li></ul><ul><li>The direction that the line of gravity takes relative to the BOS will be the direction of the resulting movement. </li></ul><ul><li>The further away the LOG is from the BOS, the greater the tendency the body has to move in that direction. E.g. Evasive running. </li></ul>Line of gravity Leg pushes against the ground Top of body moves towards LOG Direction of movement Base of support
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Centre of gravity, Line of gravity, Base of support and Physical activity <ul><li>Apply your knowledge! </li></ul><ul><li>Label the following images with the COG, LOG and BOS. </li></ul><ul><li>Is the performer stable? </li></ul>
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5 Quick Questions <ul><ul><li>Name 3 ways to ensure you are stable (use biomechanical terms) </li></ul></ul><ul><ul><li>In relation to stability, what is one advantage of being shorter? (use biomechanical terms) </li></ul></ul><ul><ul><li>When you do a right handed lay up, what movement is occurring at your right hip? </li></ul></ul><ul><ul><li>What is the agonist muscle causing this movement? </li></ul></ul><ul><ul><li>What is the antagonist muscle during this movement? </li></ul></ul>
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Force <ul><li>What is a force? </li></ul><ul><ul><li>A push, pull or twist that causes movement of an object </li></ul></ul><ul><ul><li>Force = Mass x Acceleration </li></ul></ul><ul><ul><li>Levers are used to apply a force </li></ul></ul>
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Levers – are used to apply force <ul><li>Consist of a pivot point (fulcrum) and a lever arm (connecting the pivot point to the resistance). </li></ul>Lever arm Resistance Fulcrum (pivot point) Downward Pressure
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Levers <ul><li>The amount of leverage a person processes is dependent on the length of their body , in particular the length of their arms and legs . </li></ul><ul><li>Longer levers result in greater speed at the end of the lever arms – this is beneficial for throwing and striking objects. </li></ul><ul><li>Short levers can be moved with less force and at greater speeds – this is beneficial for moving body parts quickly and applying strength for pushing, pulling and lifting objects. </li></ul><ul><li>Question: From this information, what can you assume about a shorter person in comparison to a taller person? </li></ul>
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Using Levers in Sport <ul><li>In the human body, levers are made up of the joints (fulcrum) and the bones that connect them to the objects being moved. </li></ul><ul><li>Levers in the human body can be manipulated to improve speed and apply large forces at the same time </li></ul><ul><li>Example : Running – lifting your foot and knee up will create a shorter lever, therefore you can run faster </li></ul>
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Newton’s Laws <ul><li>When exploring the area of biomechanics and human movement, it is useful to look at motion through the observations made by Sir Isaac Newton. </li></ul><ul><li>Newton was a famous seventeenth-century scientist who developed the three laws that govern all motion. </li></ul>
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Newton’s 1 st Law – The law of inertia. <ul><li>‘ A body continues in its state of rest or uniform motion unless an unbalanced force acts upon it.’ </li></ul><ul><li>In other words, a body will remain at rest or in motion unless acted upon by a force. In order to get a body moving, a force must overcome the body’s tendency to remain at rest or inertia . The amount of inertia a body has depends on its mass. </li></ul>
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Newton’s 1 st Law – The law of inertia <ul><li>This soccer ball will remain at rest, until a force acts on it </li></ul>
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Newton’s 2 nd Law – Mass, force & acceleration <ul><li>‘ The acceleration of an object is directly proportional to the force causing it, is in the same direction as the force, and is inversely proportional to the mass of the object’. </li></ul><ul><li>When a force is applied to an object it will move in the direction the force was applied, and, depending on the size of the force and the size of the object, the object will accelerate accordingly. </li></ul><ul><li>A smaller object will move faster than a larger object. </li></ul><ul><li>A greater force will move an object faster than a smaller force. </li></ul>
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Newton’s 2 nd Law – mass, force & acceleration <ul><li>Classroom experiment </li></ul><ul><li>Using the equipment you have been given, answer the questions in the workbook as a group </li></ul>
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Newton’s 3 rd Law – action & reaction <ul><li>‘ Whenever a force is applied there is an equal and opposite reaction.’ </li></ul><ul><li>If an athlete exerts a force onto the ground in order to push off, the ground will exert an equal and opposite force on the athlete, pushing them up into the air. </li></ul><ul><li>The first force of the athlete pushing into the ground is called an action force . The second force is called the reaction force (when the second body applies an opposing force back). </li></ul>
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Force summation <ul><li>To give an object momentum in activities such as throwing, kicking or striking an object, the amount of momentum given to the object is determined by ‘the sum of all forces generated by each body part’ (i.e. Force summation ). </li></ul><ul><li>To gain maximum momentum, the force needs to be generated by: </li></ul><ul><li>Using as many segments of the body as possible. </li></ul><ul><li>In the correct sequence, using large muscles first and then the smallest muscles last but fastest. </li></ul><ul><li>With correct timing. </li></ul><ul><li>Through the greatest range of motion. </li></ul>
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Application of force summation – free-throw shot technique <ul><li>In order to maximise power and efficiency of the shot, the whole body is used. </li></ul><ul><li>Your body does not move all at once. </li></ul><ul><li>The shot begins with the movement of the legs, pushing into the ground. </li></ul><ul><li>The force is then returned back up the legs, up to the shoulders, down the forearms right to the release of the ball at the fingertips. </li></ul>
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Application of force summation – free-throw shot technique
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Projectile motion <ul><li>As soon as an object is thrown it becomes a projectile . </li></ul><ul><li>A projectile is influenced by the principles that govern projectile motion – gravity, air resistance, speed height, and angle of release. </li></ul>
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Speed, height & angle of release <ul><li>Different angles of release affect the distance travelled and the height attained by an object. </li></ul><ul><li>When a ball is released from ground level, the optimal angle for release for maximum distance is about 45 degrees </li></ul><ul><li>The height of release is important when propelling an object anywhere higher than ground level. If an object needs to clear something higher than ground level (e.g. The cross bar on a goal post), the angle needs to be greater then 45 degrees. </li></ul>90 degrees 0 degrees 45 degrees Angle of release
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Height of release <ul><li>The height an object is released with determine the distance the object travels </li></ul><ul><li>e.g. </li></ul>
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