Biomechanics Flashcards
(84 cards)
1
Q
Define biomechanics
A
A branch of sports science that examines internal and external forces acting on a body, and how forces affect performance.
2
Q
Define motion
A
Movement that occurs when an object has changed position in space and in time, due to application of forces.
3
Q
3 types of motion
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Linear motion
- Movement is along a straight line, there is no rotation. All body parts move in same direction at same speed at same time.
- E.g. An ice skater gliding after they completed a movement. Cyclist who stops pedalling.
Angular motion
- Where all parts of a body move through an axis of rotation, through same angle, same direction and at same time.
- Rotary movement about an axis. All body parts do not move through same distance. Measured in degrees.
- E.g. Gymnast spinning around a bar.
General motion
- Combination of linear and angular motion.
- E.g. A cyclist riding on a straight path.
4
Q
Define distance
A
Total length of path a person or object has travelled.
5
Q
Define displacement
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Distance between point of start and finish.
6
Q
Define speed
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Measure’s distance an object travels per unit of time; how quickly an individual can cover a given distance.
Speed = Distance/Time
7
Q
Define velocity
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A measure in time of how quickly an object is covering a given distance.
Measured in meters per second.
Velocity = Displacement/Time
8
Q
Define Acceleration
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Rate at which velocity of a body changes with respect to time.
Acceleration= Final Velocity-Original Velocity/time
9
Q
Define angular distance
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Sum of all angles as a body moves from its start position to end position. Exact length of angular path.
10
Q
Define angular displacement
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Difference in angle between start and end position of body.
11
Q
Newtons first law
Linear
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An object at rest will stay at rest, and an object in motion will stay in motion unless acted upon by an unbalanced force.
When object is larger it will need more force to get it going, and it will need more force to stop it.
12
Q
Define inertia
A
Amount of resistance to a change in an object’s state of motion.
13
Q
Newtons first law
Angular
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A rotating body will continue to turn about its axis of rotation with constant angular momentum unless an external couple or eccentric force is exerted on it.
14
Q
Newtons second law
Linear
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Acceleration of a body is proportional to force applied and inversely proportional to mass of object.
15
Q
Newtons second law
Angular
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Angular acceleration of a body is proportional to torque causing it and takes place in direction in which torque acts.
16
Q
Newtons third law
Linear
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For every action there is an equal and opposite reaction.
17
Q
Conservation of linear momentum
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When collisions occur, an equal and opposite force occurs resulting in a transfer of momentum from one object to other.
18
Q
Newtons third law
Angular
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For every torque that is exerted by one body on another, there is an equal and opposite torque exerted by the second body on the first.
19
Q
Momentum
A
Measure’s amount of motion possessed by a moving body. Product of mass and velocity.
Momentum = Mass x Velocity
- An object can only have momentum if it is moving.
- Greater momentum, greater force required to stop or slow object down.
- When two bodies collide, body with most momentum will be least affected.
20
Q
Angular momentum
A
The quantity of angular motion possessed by a rotating body.
Angular momentum = Angular velocity x Moment of inertia
If mass is closer to axis of rotation, moment of inertia decreases which increases angular velocity.
If mass is further from axis of rotation, moment of inertia increases which decreases angular velocity.
21
Q
Angular momentum graph
A
22
Q
Angular velocity
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Velocity or speed of a rotating object.
23
Q
Moment of inertia
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Resistance on a rotating object to change its state of motion.
Made up by radius of rotation and weight.
MOI = mass of object x radius of rotation
Distribution of mass further away from axis of rotation, increase moment of inertia, harder to generate angular velocity.
Distribution of mass closer to axis of rotation, decrease moment of inertia, easier to generate angular velocity.
24
Q
Impulse: Force-Time
A
Application of force over a period of time to change momentum of an object.
Impulse = Force × time
Factors of impulse
- Force
- Time you can absorb force over
Application of impulse
- Force production - Increase peak force and increase time (Increase momentum).
- Force absorption - Decrease peak force and increase time (Decrease momentum).
To maximize momentum of object, increase force component.
To reduce momentum of object, increase time component.
Effects of impulse
- Create momentum
- Change momentum
- Stop momentum
25
Define lever
A rigid bar-like objects that turns around a fixed point (axis) and to which forces are applied at two other points.
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3 parts of a lever
**Axis**
* Weight/resistance/load to be moved.
**Resistance**
* Fulcrum or pivot point.
**Force**
* Application of force to move weight or resistance.
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Force arm
Distance between force and axis of rotation. Generate more force.
Force arm longer than resistance arm - Force can move resistance easier.
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Resistance arm
Distance between weight/load/resistance and axis of rotation. Generate more speed.
Resistance arm longer than force arm – body moves resistance through greater ROM.
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Function of a lever
1. Increase force - Shorten resistance arm.
2. Increase speed – Lengthen resistance arm.
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3 classes of levers
**1st Lever**
Axis/fulcrum is located in middle with force and resistance either side.
Few first-class levers in human body.
Further away force from fulcrum, object is easier to move.
Closer force to fulcrum, greater effort is needed to move object.
**2nd Lever**
Axis/fulcrum is located at one end with resistance in middle and force at opposite end.
**3rd Lever**
Axis is located at one end, force in middle, and resistance at opposite end.
In human body - muscle attachment represents force; joint represents axis/fulcrum; weight represents resistance.
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Factors affecting use of external levers
**Length of lever**
Velocity is greatest at distal end of a lever. Longer lever is heavier, greater velocity at impact, greater momentum.
**Inertia of lever**
Longer lever, greater inertia acting on it. Greater MOI, object is harder to rotate.
**Amount of force**
Amount of force athlete’s muscles can generate determines length of lever that should be used.
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Define torque
Turning effect created as a result of an eccentric force being applied around a pivot or axis.
**Torque = Force x Distance**
If force is applied further away from axis of rotation, greater torque is generated. If force is applied closer to axis, less torque is generated.
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Moment arm
Length between axis of rotation and force applied.
Every joint that is involved in an exercise has a moment arm.
Longer moment arm, greater rotational force produced for same amount of force exerted.
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Application of torque: Increase and decreasing
**Increase Torque**
1. Applying a greater force
2. Increasing length of moment arm, applying force further from axis.
**Decrease Torque**
1. Applying less force
2. Decreasing length of moment arm, applying force closer to axis.
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Concentric force
Force applied to produce linear motion.
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Eccentric force
Off centre force applied to produce angular motion.
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Force couple
Two or more forces act on a body to cancel any linear motion.
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Kinematic chain
Process that determines how to best use body segments depending on demands of a task.
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Simultaneous force
All body parts move at same time to produce a force. Used to produce accuracy, and power.
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Sequential force
All body parts move in a sequence to produce maximal force.
E.g. A baseball pitcher, striking in golf, kicking in rugby.
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Summation of forces
1. Stronger and larger muscles move first followed by smaller and faster muscles.
2. Sequentially accelerate each body part so optimum momentum passes from one body part to another.
3. Each body part should be stable, so next body part accelerates around a stable base to transfer momentum.
4. Use as many body parts as possible, so force can be applied over maximum possible time.
5. Follow through to prevent deceleration of last segment and safe dissipation of force.
6. All forces are directed towards a target.
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Define balance
Ability to neutralize forces that disturb bodies equilibrium.
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Define COG
A theoretical point in an object, located inside or outside of body, where all body’s mass is equally distributed.
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Define LOG
Is an imaginary vertical line passing down through COG to surface person is on.
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Define BOS
Area bound by outermost regions of contact between a body and support surface.
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Factors affecting balance and stability
1. Mass of object.
2. Size of base of support (BOS).
3. Height of centre of gravity (COG) above base of support (BOS).
4. Position of line of gravity (LOG) relative to base of support.
5. Increasing Base of Support in direction of oncoming force.
6. Positioning COG near edge of BOS in direction of oncoming force.
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Define projectile motion
An object propelled into air or water and affected by forces of gravity and air resistance.
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Factors affecting projectile motion
**Angle of release**
Determines trajectory shape.
Determines time object stays in air and horizontal distance moves.
Optimal angle of release for distance = 45⁰.
**Velocity/Speed of release**
Greater speed or velocity of release, greater distance a projectile will carry.
Velocity of projectile at start of release will determine height + length of trajectory as long as other factors are constant.
**Height of release**
Greater height of release of a trajectory, greater horizontal distance it will cover.
* When release height and landing height is **equal**, time for projectile to reach its peak and time it takes to land is equal. Optimal release angle **= 45°** E.g., Kicking soccer ball from ground.
* When **release height is lower than landing height**, projectile reaches its peak faster than time it lands. Optimal release angle **\<45°** E.g., Throwing
* When **release height is higher than landing height**, projectile reaches its peak slower than time it lands. Optimal release angle **\>45°** E.g., Hitting golf ball onto elevated green.
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Define COR
Measure’s elasticity of collision between an object and a given surface.
Measures how much energy remains in object after collision takes place.
Elasticity is a measure of how much rebound exists following a collision.
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How is COR measured?
Square root of height bounced divided by height dropped.
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High COR
More energy is conserved during collision, due to higher elasticity of an object.
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Low COR
Less energy is conserved during collision, due to see elasticity of an object.
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Factors affecting COR
**Equipment and materials**
Condition of balls - New ball is more elastic, higher COR.
Type of equipment - Wooden bats, lower COR.
Type of playing surface – Longer time object is in contact with surface, more energy is lost in collision. Less time object is in contact with surface, less energy lost. Clay court (high COR) vs grass court (low COR).
**Temperature**
An increase in temperature of ball results in an increase in COR.
**Velocity of collision**
Increase velocity increases compression of ball during collision, increasing amount of elasticity it loses (decreases COR).
Increase velocity = decrease COR
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Fluid mechanics
Study of how a person or object moves through a fluid, and forces associated with creating movement.
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Fluid resistance
As an object moves through a fluid (air or water), it is disturbed by fluid resistance.
Greater disturbance to fluid, greater transfer of energy from object to fluid.
**Density (air)**
Denser fluid, more disturbed fluid, greater resistance.
E.g. Humid conditions, more dense conditions, ball will encounter greater levels of air resistance.
**Viscosity (liquid)**
More viscous fluid, more disturbed fluid becomes, hence greater resistance.
E.g. Honey is more viscous than water, water is more viscous than air.
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Define form drag
Resistance created by pressure difference between front and back of object moving through a fluid.
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Factos affecting form drag
1. **Cross Sectional Area** of object/ **Shape of Object**
* CSA changes amount of SA exposed to oncoming air flow. Change’s turbulence pocket, therefore, pressure difference between front and back of an object.
1. **Velocity of Object**
* Change’s time of boundary layer separation and turbulence - changes pressure difference between front and back.
1. **Surface Roughness**
* Change’s time of boundary layer separation – alters pressure difference between front and back
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Define surface drag
Friction/resistance produced between fluid and surface of a moving object.
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Factors affecting surface drag
1. **Velocity of moving object**
* Speed of object changes boundary layer separation. Earlier boundary layer separates, greater resistance/drag.
* Golf ball dimples allow later boundary layer separation.
* Swimmers wear tight fitting swimsuits, shave body and wear lotions.
1. **Viscosity of fluid**
* The density of the fluid changes the amount of resistance on a body. Denser fluid, greater resistance.
1. **Surface area of object**
* Greater SA in contact with surface increases friction/resistance on moving body.
60
Define wave drag
Resistance formed by creation of waves at point where air and water interact.
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Factors affecting wave drag
1. **Relative velocity of wave**
* Greater velocity, more resistance/friction, greater wave drag.
1. **Technique of swimmer**
* Streamlined technique of swimmer, reduce effects of wave drag.
1. **Overreaching**
* Pulling the water with each stroke will cause body to move through own waves causing resistance.
1. **Open water vs. closed conditions**
* Lane ropes reduce wave drag by dissipating moving surface water.
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Reduction of drag - Application to cycling
Surface drag, form drag.
**Surface drag** - smooth, tight fitting clothes, shave legs.
**Form drag** - streamlined position reduce CSA, aerodynamic rims, aerodynamic helmets, aerodynamic bike components.
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Boundary layer
Thin layer of air surrounding or attached to ball.
**Laminar** (smooth flow, large turbulent pocket at back of ball).
**Turbulent** (rough flow, small turbulent pocket at back of ball).
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Boundary layer speration
Where boundary layer breaks away from ball.
Earlier boundary layer separation, greater pressure gradient between front and back of ball. Leads to ↑ drag.
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Factors affecting boundry layer seperation
**Rough surface**
Boundary layer separation occurs later, small pocket of turbulent at rear of ball. Smaller pressure differential between front and back of ball.
**Smooth surface**
Boundary layer separation occurs earlier, large turbulent pocket at rear of ball. Larger pressure differential between front and back of ball.
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Factors affecting boundary layer seperation: Velocity
**Low velocity**
Boundary layer separation occurs later, small turbulent pocket at rear of ball. Smaller pressure differential between front and back of ball.
**High velocity**
Boundary layer separation occurs earlier large turbulent pocket at back of ball. Larger pressure differential between front and rear of ball.
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Factors affecting boundary layer seperation: Shape
**Oval ball**
Boundary layer separation to occurs later. Smaller pressure differential between front and back of ball; small turbulent pocket at rear of ball.
**Round ball**
Boundary layer separation to take place earlier, large turbulent pocket at back of ball. Larger pressure differential between front and rear of ball.
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Factors affecting boundary layer seperation
Drag coefficient
CSA
Mass of the object
**Drag coefficient:** Measure used to quantify drag or resistance of an object in a fluid environment. Directly related to CSA.
**Boundary layer seperation:** Linear relationship exists between CSA exposed to air and drag. ↑ CSA = ↑ drag
**Mass:** Greater mass of ball, less drag.
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Turbulent Flow
Flow in which velocity at any point varies erratically.
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Laminar flow
A type of fluid flow in which fluid moves smoothly in individual layers.
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Buoyancy
Upward force that keeps things afloat. Used to counteract effects of gravity. How well a body floats or how high it sits in fluid.
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Lift forces
* Refers to component of force that acts perpendicular to direction of flow.
* Act at a right angle to direction of motion.
* Act in both an upwards and downwards direction.
* Only occurs in objects which are spinning (magnus) or not perfectly symmetrical (Bernoulli’s).
* Lift is created by different pressures (high/low) on opposite sides of an object due to fluid flow past object.
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Bernoulis principle
**As velocity of fluid increases, pressure fluid exerts on an object decreases. Velocity inversely proportional to pressure.**
Only applies to unsymmetrical objects.
* Higher velocity on superior surface of object, lower pressure. Low velocity on inferior surface, higher pressure; creates an upward lift force. E.g. Airplane wing creates lift in an upwards direction to keep in air.
* Low velocity on superior surface, higher pressure. High velocity on inferior surface, lower pressure; creates a downward lift force. E.g. Racing car creates lift in a downwards direction to keep it on ground.
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Magnus effect
Describes effect of rotation on an objects path as it moves through fluid.
Applies Bernoulli’s principle to explain effect spin has on trajectory or flight path of an object.
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Spin
Ball struck with eccentric force, has both linear and angular rotation.
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Top spin
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Sidespin
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Back spin
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No spin
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Qualitative analysis
Analysis of fundamental variables that cannot be precatively valued.
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Quantitative analysis
Direct measurable, numerical examination of specific variables.
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Qualitative analysis of movment skills
1. Assessing athletes.
2. Identifying a profile of strengths and weakness for individuals and team.
3. Amending training program to correct weaknesses.
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Examples of observation checklists
Badminton skills checklist.
Observation of game performance.
Score cards.
Marking key.
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Knudsen and Morrison’s model of qualitative analysis
**Preparation**
Coach gathers info on key technical aspects of activity. Coach communicates with athlete and learns personal goals. When preparing to analyse a player, coach should allow them to complete activities that allow demonstration of desired goals.
**Observation**
Plan a suitable vantage point and method of recording observations. Who will observe, record, what time frames?
**Evaluation**
Review the analysis and ascertain players strengths and weaknesses. Then, place weakness into a priority list that has scheduled points for potential intervention.
**Intervention**
Discuss weaknesses with athlete. Methods for intervention will be based on type of skill being considered. Any error correction should be timetabled for out of season.
