Biomechanics Flashcards
Segmental/sequential interaction
The transfer of momentum across the joints to provide maximum force
What principles are applied to produce maximum force efficiently? (5 points)
- Use large muscle groups with the largest mass first (legs)
- Sequentially accelerate each body part so that optimum momentum passes from one body part onto the next
- Each body part should have a stable base so that optimum momentum passes from one body part onto the next
- follow through become vital so as the final segment doesn’t not decelerate in the final stages
- ensure all forces are directed towards the target
Simultaneous movement
movement where all body parts move at the same time to produce a force
optimal projection
the relationship between the angle, velocity and height of release/ landing height to attain the goal of the athlete
3 factors which determine the trajectory of the flight path:
- height of release
- velocity of release
- angle of release
angle of release
considers the vertical and horizontal trajectory
athletes should throw/release the projectile approximately at a 45 degree angle to ensure the greatest distance covered
velocity of release
dependant on the force applied-more force=more distance covered
Height of release
if the projectile is released from a higher= flight time is longer=longer distance covered
if the projectile is released lower=decrease in-flight time=shorter distance covered
optimise the distance covered by releasing from the highest point
Force-motion
an object’s motion is affected by the magnitude and direction of an external acting force
What are the three principles of force-motion?
- size or magnitude of a force
- the more acceleration of an object, the more impulse/momentum gained
- direction of the force applied
Force motion principles in detail
- Size or magnitude of force- more force applied the greater the acceleration of the object
- The more acceleration of an object, the more impulse/momentum gained- faster means harder to stop
- Direction of force applied-force is applied in the direction of the target will increase the transfer of momentum through the object or target (up for high jump, out for long jump)
Linear motion
the object’s height/mass determines its inertia
angular motion
an object’s inertia or moment of inertia has two components:
it’s weight and mass and the distance that the weight of the object is distributed away from the axis of rotation
greater angle and mass= more inertia
increase speed to create force
motion
mass and acceleration
Moment of inertia
the resistance of the rotating object has to change its state of motion
- the closer the mass is distributed to the axis of rotation, the easier it is to rotate because its able to generate more angular velocity
- shorten the axis of rotation= lower MOI=faster
angular velocity
- Moment of inertia increases angular velocity decreases
* Moment of inertia decreases angular velocity increases
Angular momentum
conservation of angular momentum means that a spinning body will continue spinning indefinitely unless external forces act on it
- it its constant and only changes once it hits the ground
??? momentum
the amount of angular motion possessed by a rotating body measured as a product of MOI and angular velocity
(spinning- furthest away=spins faster)
(greater mass of an object and faster it moving=harder to slow down and stop)
how do we change rotational inertia?
- Change the radius of rotational inertia (hands closer to the axis as it reduces MOI)
- Change the mass of the object (a heavier or lighter piece of equipment and move the mass of the object away from axis and increase MOI)
levers
A rigid bar-like object that turns around a fixed point to move an object at one end by applying pressure to the other
Three elements of levers
axis (joints)
resistance (weight of an object or limb)
force (contracting muscle)
force arm (levers)
distance from the axis (joint) to muscle attachment of the bone
dictates our ability to apply force
larger force arm= more force produced (bar closer to the body to generate more force)
resistance arm
the distance from the axis (joint) to the resistance
dictates our ability to apply velocity/speed
larger resistance arm=more speed/velocity generated
shorten force arm and increase resistance arm to increased speed
types of lever
first-class (A in the middle) second class (R in the middle) third class (F in the middle)
first class lever (examples)
extension of forearm head nodding (R=chin, A=spin, F=muscle) shooting ball (tricep extension)
second class levers (examples)
standing on your toes (A=toes, R=body, F=calf muscle)
push up
wheelbarrows
third class lever (examples)
flexion/extension
elbow flexion
hip extension
why do we use levers?
increase the momentum and acceleration of imparted objects
principle of leverage
the longer the lever the greater the velocity produced and therefore the greater velocity impact, the greater transfer of acceleration and momentum
Key concept: maximizing lever length at the point of impact ensures max speed at the impact or release point
Three factors that influence levers
length of the lever
inertia of the lever
size of force
length of the lever (impacting levers)
the max linear speed of any part of a moving lever occurs at the furthest point of the axis
Golfers increasing the length of their driver, results in longer drivers because bat bits ball at a greater speed
Inertia of a lever (impacting levers)
a longer levers, the heavier it usually is and therefore the more difficult it is to rotate (higher MOI)
Size of force (impacting levers)
a longer, heavier, external lever allows an athlete to project an object further, but it requires greater muscle strength to handle the implement effectively
Torque
a measure of the force that can cause an object to rotate about an axis
- Further away from the axis point, the higher the torque produced, and less force required to start
- The closer to axis point, the lower the torque produced and more force required to start
changing torque
- Change the size of the force being applied (more/less)
2. Manipulate the distance away this force is applied to the axis of the object
Size of the force (changing torque)
size of the torque depends on the size of the force applied to the axis
(the bigger the force applied, the more torque produced)
Distance of the force being applied to the axis (changing torque)
vary the perpendicular force applied to the axis
Create a bigger moment arm and hence the potential to create increased torque
Newtons 2nd law of motion (law of acceleration and momentum)
When a body is acted upon by a constant force, its resulting acceleration is proportional to the force and inversely proportional to the mass
Momentum
the amount of motion possessed by a moving body, measured as a product of its mass and velocity (only momentum when it’s moving)
more momentum= more force needed to stop it
when two bodies collide, one with greater momentum with have the least effect
Conservation of momentum
when a collision occurs, the total momentum of two bodies before impact is equal to the total momentum after impact
(pool balls example)
Force-time (impulse)
the size of a force and the amount of time the force acts on an object indicates the amount of impulse applied (change in momentum)
Impulse-momentum relationship
The time that force is applied is equal to the change in momentum that is produced
Change in momentum= impulse
Key factors/points of impulse (4 points)
- longer and greater a force can be applied, the greater the object impulse/change in momentum
- impulse experienced by an object always equals the change in momentum
- for the impulse to occur it must be in contact with something
- bigger the impulse, the bigger the change in momentum leads to a greater level of acceleration (velocity/speed) positive or negative
how do we change impulse?
- increasing or decreasing the size of the force applied
2. increasing or decreasing time of the force applied to the object
increasing or decreasing size of the force applied (changing impulse)
If the length of the time is constant, the impulse can only be increased by increasing the size (strength) of the force applied
For example: the rower needs to use greater force withs legs and upper body to increase impulse which will change the momentum
increasing or decreasing time of the force applied to the object
impulse can only be increased by increasing the time of the force applied
(hold onto it for longer=more control and force generated)
5 sporting techniques to maximise impulse:
- Large backspin
- Wide stance
- segmental interaction before release
- follow through before release
- flattening the arc
maximising impulse (large backspin)
Enables a high level of force to be applied but the stick is only in contact for a short amount of time
maximising impulse (widen stance)
Enables high level of contact time but will only generate limited force (applies to throwing, kicking, and hitting)
maximising impulse (segmental interaction before release)
enables a high level of forces to be applied through effective muscle force summation (applies to throwing, kicking, and hitting)
maximising impulse (follow through before release)
enables high level of contact time (applies to throwing, kicking, and hitting)
maximising impulse (flattening the arc)
enables high level of contact time (applies to throwing, kicking, and hitting)
What does flattening the arc look like? (Technique in sport)
- allows longer contact with the ball when throwing or hitting
- used where body parts or an object move in a straight line at the point or released during the application of impulse
- helps increase accuracy and success by having more than one chance to hit or release the ball as a contact point
Flattening the arc while throwing
- body rotating shoulder joint forward in the direction of the throw just prior to the time of the release of the ball
- transference of the weight onto the front leg just prior to contact
- stablishing (locking) the front leg to transfer momentum (summation of forces) and therefore increase the force
Flattening the arc while striking
- body rotating the trunk that moves the shoulder forward
- transference of weight onto the front leg just prior to contact
- stablishing (locking) the front leg to transfer momentum (summation of forces) and therefore increase force
Decreasing momentum (force absorption)
force absorption: smaller force is used over a longer period, decreases momentum which has an impact on impulse
co-efficient of restitution
the ratio of relevant velocity (or height) after impact to the relevant velocity (or height) before the collision
Key elements of co-efficient of restitution
• measures the bounciness of a ball, conservation of momentum/energy, and the elasticity of the collision
• a number that indicates how much kinetic energy remains after the collision of two objects
• can be determined by dropping a ball from a given height and then measuring the height of its rebound
(measured on a scale from 1-0)
COR of 1
a perfectly elastic collision, when a ball is dropped from a given height the ball rebounds to that same height
COR will be less than 1.0 because the impact creates a transfer for some momentum from the ball to the surface (momentum lost in heat and sound)
COR of 0
a perfectly inelastic collision, when a ball is dropped, it doesn’t bounce at all
COR (A ball with high bounce)
• The higher a ball rebounds or bounces after impacts, the higher its COR, and hence the greater its elasticity (ability to regain its shape)
• little energy is lost with the surface
The greater the elasticity of the object, the faster it will return to its original shape and the further it will rebound after impact
COR (A ball with low bounce)
- The lower the ball rebounds or bounces after impact, the lower the COR, and hence the smaller it’s elasticity (ability to regain its shape)
- Most energy is lost on the surface
Factors affecting the COR: (5 factors)
- Type of ball
- Type of striking equipment
- Playing surface
- Temperature of materials
- Velocity of impact
Factors affecting the COR: type of ball
- New balls in sports have a higher COR than older balls
* Inflated balls have greater COR than deflated or underinflated balls
Factors affecting the COR: Type of striking equipment
- Materials of the bats can affect COR
- Tennis racquets that are tightly strung have a greater degree of elasticity than racquets that are strung with lower tensions
Factors affecting the COR: Playing surfaces
- Some surfaces are more or less elastic than others, resulting in the same ball will rebound somewhat differently from these different surfaces
- Court surfaces affect the height and speed of rebound of the ball
Factors affecting the COR: Temperature of the ball
- As the temperature of the ball increase there is a corresponding increase in the COR
- As it heats up the pressure inside the ball increases and makes it play faster (increases COR)
- If the wheatear is cold, it will result in lower elasticity which equals lower COR
Factors affecting the COR: Velocity of the ball
- there is an optimum impact speed in any hitting sport
- The harder the hit, the greater the compression of the ball
- Balls must have some elasticity, or they will shatter at impact
Drag
forces laced on moving objects due to the flow of a fluid (air/water) contacting the object
4 Environmental factors affecting drag
Air density: Higher altitudes, less drag
Atmosphere pressure: Increased pressure, increased density, higher drag
Humidity: Increased humidity, increased density, higher drag
Temperature: Increased temperature, decreased density, less drag
3 Forms of drag
- Surface/skin drag
- Form
- Wave
Surface drag
the drag is created due to a fluid moving over an object resulting in friction between the surface of the body and the fluid
Factors affecting surface drag (V, SA, SR, VIS)
- Velocity of the moving object:
• At higher speeds, athletes experience greater levels of surface drag - Surface area of object:
• The size of the area in contact with the fluid - Surface roughness of the object:
• Smooth surface (tight-fitting clothes) leads to reduced surface drag by reducing surface friction - Viscosity of the fluid
Reducing surface drag
- Advances in equipment (better waxes for boards)
- Advances in clothing materials (swimsuit designs)
- Wearing tight and light clothing
- Shaving all hair off
Form or pressure drag
the drag created by a pressure difference between the front and rear of an object moving through fluid (most important)
Factors affecting form/pressure drag (V, SA, SR, S)
- Velocity of the moving object:
• at higher speeds, athletes experience greater levels of form drag - surface area of the object (cross-sectional):
• cyclist of upright vs crouched position - surface roughness of the object
- shape of the object:
• round ball vs oval ball
Reducing form/pressure drag
- advances in equipment: streamlined designs (fins on boards or boats, helmets create pressure differences)
- drafting or slipstreaming: capitalizes on low pressure (eddies) created by the athlete in the front as you try to hook the suction effect
- streamlining using skill techniques: maintain a streamlined position (cyclists bend over handlebars, swimmers lie flat, runners run will straight arms)
Wave drag
when a body moves through the water it causes waves to be generated causing resistance to movement (occurs where water and air meet)
Factors affecting wave drag (V, S, O&C)
- velocity of the moving object:
• greater the velocity, the greater the wave drag - Streamlining:
• The body or equipment - Open water (ocean) vs closed conditions (pool):
• Conditions flat vs choppy
Reducing wave drag
- Advancing equipment (curving the shape, increasing buoyancy, lane ropes to help spread waves, wearing a wet suit to decrease surface area)
- Streamlining: by being more streamlined in the water, swimmers can reduce the effects of wave drag (a longer stroke lets you use slower, more controlled turnover at any speed, which means less turbulence, fewer waves, less drag
Boundary layer
a thin layer of air surrounding or ‘attached’ to a projectile as it moves through the air (laminar or turbulent)
Laminar (smooth flowing)
A type of fluid flow in which fluid moves smoothly in induvial layers or streams
Turbulent (tough flowing)
when fluid flows in an irregular pattern causing mini whirlpools/swirls
Separation point
the point on the object where the air flow starts to move away from the object (air moving towards the object is deemed to be laminar and after the separation points more turbulent)
low velocity and high velocity
- When an object is at LOW VELOCITY it only creates a low level of drag because there are very few ‘eddies’ or small wake caused (smooth balls)
- When an object is at HIGH VELOCITY it creates a high-level pf of drag because there are lots of ‘eddies’ or wake caused (smooth balls)
Dimples on objects: reduces drag
More stick later separation=less turbulent flow=less drag
Dimple ball:
• High pressure in front of the ball
• Smaller low-pressure area at the rear of the ball means less drag
• There is a pressure different from front to back
Stitched balls: the ball will go in the direction to the stitches (same effect of dimples)
Smooth ball
High pressure in front of the ball
Larger pressure at the rear of the ball means more drag
Bernoulli principle
related to the pressure created from a moving fluid over an object (deals with lift)
The velocity of a fluid moving over an object is inversely proportional to the pressure on the object
Lift key guiding principles and rules:
- On one side the air moves slower because it has less distance to travel and as a result, it has high pressure (high pressure=low velocity)
- On one side the air moves faster under the curve because it must move the distance to travel it has low pressure (low pressure=high velocity)
- The ball will travel high to low (always towards the low pressure)
Magnus force
used to describe the effect of rotation on an objects path as it moves through a fluid (applies to Bernoulli’s principle to an object with spin)
Magnus force/effect guiding principles:
- Air moving in the same direction as the boundary air caused by the spin speeds up (high velocity and low pressure)
- Air moving in the opposite direction as the boundary air caused by the spin slows down (low velocity and high pressure)
- The ball will always swerve in the direction of high to low pressure
Spin
- Topspin
- Backspin
- Sidespin
When the ball has backspin, topspin or sidespin, the Magnus effect changes the flight path of the ball from what would have been without spin
Topspin:
- Eccentric force is applied above the center of gravity (on top of the ball)
- Flight path: ball dips down sharply in the air, shortening flight time
- Rebound: greater horizontal velocity after bounces, comes onto players quicker, and rebounds low
- Angle of incidence: low
- Angle of reflection: high
Backspin:
- Eccentric force is applied below the center (under the ball)
- Flight path: flatter than topspin
- Rebound: slower horizontal velocity, kicks back and results do not come on to the player and bounce higher giving it a better chance of it going in
- Angle of incidence: high
- Angle of reflection: low
Sidespin:
- Eccentric force is applied on the side of an object
- Flight path: curves in the direction of the spin while in flight
- Rebound: on landing will bounce in the opposite direction
- Hook: side spin moves the ball to the left
- Slice: side spins move the ball to the right
- Leg break: swings to the right hits the ground and bounces left
- Off break: swings to the left hits the ground and bounces right
No spin
• Leaves the ball up to that natural wind to take it in a direction
Range of motion
measurement of movement around a specific joint or body part (flexibility)
Balance
the ability of the body or object to maintain or hold its position
stability
the ability of a body to resist distributing this balance (static or dynamic)
centre of gravity
- It is an imaginary point and can be inside or outside the body and change with the movement
- A person’s centre of gravity changes as they change body position (moving your arms above your head raises the centre of gravity, the right arm only= moves centre of gravity to the right)
Key factors affecting stability and balance
- Size of the objects’ base of support
- Position of the line of gravity and centre of gravity
- Height of the centre of gravity above the base of support
- Mass of the body (its weight)
- Size of the object’s base of support (affecting stability and balance)
- The greater the area of support, the greater the degree of stability
- More stable:
- High base of support-4 points in contact with the ground
- Lower COG-closer to the ground
- Less stable:
- small base of-two points in contact on the ground
- Feet very close together
- 3.higher COG: well of the ground
- WIDEN BASE OF SUPPORT BY MOVING LEGS WIDER APART
- Position of the line of gravity and centre of gravity (affecting stability and balance)
- the closer the line and centre of gravity is to directly over the middle of the base of support, the greater the stability of the body
- movement can only occur, when the line of gravity falls outside a person’s base of support
- shifting a person’s centre of gravity closer to their edge makes them less stable but quicker to move as a result
- BEND KNEWS AND PUSH BUM OUT TO BE CLOSER TO COG, MOVES FORWARD EASIER
- Height of the centre of gravity above the base of support (affecting stability and balance)
- the line of gravity or pull of gravity will always pass vertically through the centre of an objects mass
- the higher the centre of gravity above the base of support, the lower stable object is
- athletes often lower their COG by bending their knees in order to increase their stability
- upright= higher COG, bent= lower COG
- the lower the COG, the greater the stability of the body
- BENDING KNEES
- Mass of the body (its weight)
- The greater the mass, the greater the stability
* INCREASE MUSCLE AND WEIGHT TO BECOME MORE STABLE
