Biomechanical terms - Definitions PDF

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Biomechanics Terms Force Is the product of mass x acceleration (F=MA). Force-Motion is the application of force to produce motion.

Inertia Is a body’s resistance to change its state of motion.

Acceleration Occurs when a force acts on a body and changes its state of motion

Momentum A property of any moving body and a result of (mass x velocity)

Velocity Speed in a given direction

Newtons Laws of motion •

Newtons first law (law of inertia)

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“A body continues in its state of rest or state of motion unless acted upon by a force”

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Newtons second law (law of acceleration)

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“The rate of change of acceleration to a body is proportional to the force applied to it and inversely proportional to the mass of the object”

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Newtons third law (action reaction)

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For every action there is an equal an opposite reaction.

Conservation of momentum The principle states: the total momentum of two objects before and after impact are equal

Coefficient of Restitution: The technical term for the elasticity of a ball/implement/surface and relates to the bounciness of an object COR can be measured à height of rebound divided by height of initial drop Factors affecting COR 1. Equipment and materials (titanium and aluminium more elastic than wood) 2. Temperature (the more heat = the higher COR) Impulse: “the application of FORCE over a period of TIME to change the MOMENTUM of an object” Impulse = Force x Time We can think of Impulse as either being ‘positive’ or ‘negative’ Positive impulse Ability to exert high force and increase momentum on an object Therefore, the longer the force can be applied, and the greater the force that is applied, the greater the objects impulse or change in momentum Sporting links: 

Shot put – standing start V glide with rotation. The glide method provides more time for force to be developed, therefore a greater impulse and more momentum produced.

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High Jump – the position of the foot at the final take off goes from a heel strike, to flat foot to toe off (rather than simply toe off as in the case of sprinting).

Negative Impulse Negative impulse is associated with decreasing momentum (there is a stopping force involved) In negative impulse examples the variable which can largely be modified is time. In almost all examples athletes try to decrease momentum by absorbing force over a long period of time. Cricket – catching a ball •

Give with the hands in the same direction as the incoming ball.

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Bend at elbows

Why: this increasing the time which the force is absorbed – meaning more chance of catching the ball/less pain endured

Angular motion Is circular motion and occurs when a body moves around an axis of rotation.

Moment of Inertia Definition: “Refers to the resistance to rotational (angular) motion OR the resistance of a rotating object to change its motion.” Formula = mass x radius of rotation How to manipulate MOI 1. By moving the mass of an object further away from the axis of rotation à the radius of rotation increases which results in the moment of inertia increasing. 2. By increasing the mass of an object à the MOI increases.

Angular Momentum The quantity of angular motion possessed by a body OR The amount of momentum something has whilst spinning Formula = Angular Velocity x Moment of Inertia Conservation of Angular momentum Means that a spinning body will continue spinning indefinitely unless acted upon by an external force. Conservation of momentum applies to sports such as gymnastics, diving, aerial skiing à think sports where athletes get airborne In these sports, an inverse relationship exists between moment of inertia and angular velocity.

But use this anagram to help you remember BOSSCRIFF: 

Balance

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Optimal projection

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Spin

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Segmental interaction

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Coordination continuum

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Range of motion

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Inertia

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Force-motion

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Force-time (impulse)

Balance The stability of an object is dependent on where the line of gravity is in relation to the base of support. Stability can be improved by : 1. Increasing the base of support à widening stance/ increasing amount of contact with limbs/stick. Bigger base of support = more balanced 2. Lowering the COM à Bending knees 3. Increasing the mass of a body à it depends where the extra mass is, but generally speaking, more mass = more balanced. 4. Ensuring COG is within the base of support. If COG falls within the base of support à more balance

Optimal Projection Principle identifies that for any movement involving projectiles, there is an optimal projection depending on what is trying to be achieved. The projection is determined by: 

Velocity of release

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Angle of release (generally speaking a release of approx. 45 degrees is optimal for maximising distance)

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Height of release

Spin - already have notes down the page

Segmental Interactions Is when energy is transferred across body segments (EG. From the shoulder à upper arm à lower arm à wrist.

Coordination continuum Coordination involves the sequencing and timing of body actions to create movement.

Range of motion Refers to extent of motion around a joint

Inertia Force motion - all three have notes above ^^ Force Time

Levers Levers have 3 main parts that you must be able to identify: •

Fulcrum (or axis) – point around which the levers rotates

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Resistance (or weight) – which needs to be moved

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Force – which moves the resistance/weight

It is also very important that you understand the following two terms: 1. Resistance arm: distance between fulcrum and the resistance. 2. Effort arm: distance between the fulcrum and the force being applied

First class lever Fulcrum (axis) is between resistance and force - See saw Primary function – it is dependant on the fulcrum location – it can be to increase speed OR to magnify force (demo)Best example is triceps extension

Second Class Lever think strength (large force arm) Fulcrum at end of lever, resistance in middle and force at other end - wheel barrow Primary function – magnify the application of force (Force arm is long) Example in human body: Push up + Calf raise

Third Class Lever think speed (Long resistance arm) Fulcrum at the end, force in the middle, and load at the other end Primary function - increase speed (they have large resistance arms) Gold medal example: Bicep Curl

Torque Is what brings about a turning effect around a fulcrum. Is best described as a twist “Measures how hard (not fast) something is rotated about an axis” Torque = force x perpendicular distance of the lever arm (from axis) Factors which affect the amount of torque placed on a body include: Amount of force applied (through muscular contraction) Length of moment arm à longer moment arm = production of more torque

Bernoulli’s principle “States that as the speed of a moving fluid increases, the pressure within that fluid decreases.” Speed is INVERSELY PROPORTIONAL to pressure (fast flow à pressure low) Bernoulli’s Principle explains LIFT forces which have a large impact in different sports Lift forces are created when there are areas of high pressure and low pressure. For lift to occur – there must be a pressure differential between the two sides of a body.

Magnus effect Is the effect that spin has on an objects path, as it travels through a fluid (remember air is classified as a fluid)

Types of Spin and magnus effect

TOP Spin Eccentric force applied to top of ball Flight path Ball drops more quickly à shorter flight path Flight Path explained High pressure is on top of ball (surrounding fluid is moving slowest here) Low pressure is on bottom of ball (surrounding fluid is moving fastest here) Air wants to move from areas of high to low pressure – in this case, from top to bottom à Magnus force is DOWNWARDS à therefore ball drops more quickly in flight Example and advantage Forehand tennis à can hit the ball with greater velocity, but still have ball bounce in court due to ball dipping. Lob (tennis) à can clear opponents reach who is standing at net, but ball still lands in court

BACK spin Eccentric force applied to bottom of ball Flight path Longer flight path – ball stays in air longer, travels further distance Flight Path explained High pressure is on bottom of ball (surrounding fluid is moving fastest here) Low pressure is on top of ball (surrounding fluid is moving slowest here) Air wants to move from areas of high to low pressure – in this case, from bottom to top à Magnus force is UPWARDS à therefore ball stays in flight for longer and travels further distance. Example and advantages Drive in golf, soccer goal kick à ball is in air longer, travels further which is ideal in these examples à ball is closer to hole, etc. Tennis slice à ball is in air longer, therefore is a slower shot à can be used as a defensive weapon so player can get back to good court position.

Side Spin Eccentric force applied to one side of ball Flight path Ball will move laterally – either right or left. Flight Path explained For balls that move right to left: High pressure is on right side of ball (surrounding fluid is moving slowest here) Low pressure is on left side of ball (surrounding fluid is moving fastest here) Air wants to move from areas of high to low pressure – in this case, from right to left à Magnus force is RIGHT TO LEFT à therefore ball drops more quickly in flight Example and advantage •

Soccer free kick à necessary to move the ball around a ‘wall’

NO Spin Application of a concentric (in dead centre) force Flight path ball moves erratically through the air due to turbulent flow Unpredictable flight path Flight Path explained Because there are no areas of high and low pressure being formed – there is no Magnus force at play. As such the Flight path is highly variable and influenced largely by external variables such as wind. Example and advantage •

Floater serve in Volleyball à ball moves erratically through the air so it is hard to judge and make a successful dig/set.

Effect of spin on bounce Top spin •

Ball skids on (has a lower trajectory)

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Has comparatively more forward momentum

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Does not bounce as high.

Back spin •

Kicks up (has a high trajectory post bounce)

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Has comparatively less forward momentum

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And a higher bounce...