Biomechanics Flashcards
3.1 principles - newton and 3.2 stability and lever systems
What is Biomechanics?
Study of human movement and the effect of force and motion on sports performance
How does the laws and principles enables performers and coaches
Analyse performance
maximise perfomance
reduce or prevent injuries
design equipment
What is Newton’s first laws of motion?
Law of Inertia-
A body continues in a state of rest or uniform velocity unless acted upon by an external or unbalanced
Eg- the greater the mass of the sprinter the greater the force needed to accelerate away from the blocks.
What is inertia-
The resistance of a body to change its state of motion
Apply Newtons first law of motion for a 100m sprinter?
The 100m sprinter will remain at rest in the blocks until an external force large enough to overcome their inertia creates motion.
Equally when the sprinter reaches constant velocity, they should continue at that constant velocity until an external or unbalanced force acts upon them to change.
What is velocity
The rate of change in displacement. This is a term used throughout this chapter and although closely related to speed, includes a directional element
What is Newton’s second law of motion?
law of acceleration-
“A body’s rate of change in momentum is proportional to the size of the force applied and acts in the same direction as the force applied”
Apply newtons second law
The greater the force applied to the sprinter the greater the rate of change in momentum and therefore acceleration away from the blocks. The force is applied in a forward direction so the sprinter drives towards the line.
What is momentum
the quantity of motion possessed by a moving body
Momentum (kgm/s) = Mass X velocity
What is acceleration?
The rate of change in velocity.
Acceleration (m/s/s) = (Final velocity - initial velocity) / time
What is newtons third law of motion
law of reaction
“For every action force applied to a body there is an equal and opposite reaction force”
Apply newtons third law
when the 100m sprinter applies a down and backward action force into the blocks, the blocks provide an equal and opposite up and forward reaction force to the sprinter to rive them out the blocks
Calculation for velocity
Displacement m / time taken s
(m/s)
Calculation for momentum
mass x velocity
(kgm/s)
Calculation for acceleration
(Final velocity- inital) / time taken
(m/s/s)
What is force
A push or a pull that alters the state of motion of a body
Internal force generated by the contraction of skeletal muscle
External force comes from outside the body and acts upon it.
calculation of force
Mass x acceleration
measured in newtons (N)
What are the 5 effects force can have?
1- Can create motion
2- Can accelerate a body
3- Can decelerate a body
4- Can change the direction of a body
5- Can change the shape of a body
using a football penalty- explain how force affects it
1- The football will remain at rest on the penalty sport until a force is applied
2- The greater the force applied by the footballers foot to the ball, the greater the rate of acceleration towards the goal.
3- the ball moves through the air towards the goal, the force of air resistance will act in the opposite direction and slow it down
4- as the goalkeeper dives to save a high corner shot, he will apply a force from his hands to the ball, changing its direction pushing it way from goal
5- if the goalkeeper fails to make the save, the force of the ball coming into contact with the net will make the net change shape
What is net force?
The sum of all forces acting on a body. (also known as resultant force)
If a net force is present, there is a change in motion as the forces are unbalanced
What are horizontal and vertical forces in netforce
the vertical that push a body up and pull a body down and
the horizontal forces that push a body forwards and pull it backwards
What are balanced forces
These occur when two or more forces acting on a body are equal in size and opposite in direction.
Net force = 0, the body will remain at rest or in motion with constant velocity
What are unbalanced forces
These occur when two forces are unequal in size and opposite in direction.
A net force will be present and the body will change its state of motion, either accelerating or decelerating
What are the vertical forces
weight and reaction
What is weight
gravitational pull that earth exerts on a body and is measured in newtons
weight is always present and acts downwards from the body’s centre of mass.
calculation of weight
mass x acceleration due to gravity
(N)
What is Reaction
Is the equal and opposite force exerted by a body in response to the action force placed upon it
What is reaction measured in
Newtons
What are the Horizontal Forces
Friction and Air resistance
What is friction
The force that opposes the motion of two surfaces in contact
What is Friction measured in?
Newtons
What factors affect friction?
Roughness of ground surface
Roughness of contact surface
Temperature
Size of normal reaction
How does the roughness of the ground surface affect friction?
Increased roughness = Increased friction
How does the roughness of the contact surface affect friction?
Increased roughness = friction increased
How does temperature affect friction?
Increased temp of ground and contact surface = friction increased
How does increasing the size of normal reaction affect friction?
Increasing size of normal reaction = increased friction
What is air resistance?
A force that opposes the motion of a body traveling through the air
What is air resistance measured in?
Newtons
What factors is air resistance affected by?
Velocity
shape
Frontal-cross sectional area
Smoothness of surface
How does velocity affect air resistance
Increasing velocity= increased air resistance
How does shape effect air resistance
More aerodynamic the shape = lower air resistance
How does frontal cross-sectional area affect air resistance?
decreasing frontal cross-sectional area= decrease air resistance
How does smoothness of surface affect air resistance?
Increasing smoothness = air resistance decrease
What is streamlining?
The creation of smooth air flow around an aerodynamic shape to minimise air resistance
What is a free body diagram?
A clearly labelled sketch showing all of the force acting on a body at a particular instant in time
What is the origin and direction of the arrow for weight in a free body diagram
From the centre of mass - downwards vertically
What is the origin and direction of the arrow for reaction in a free body diagram?
From the point of contact extending vertically upwards
What is the size of the arrow and relationship between weight?
If weight is equal in size to reaction (W=R), net force is zero.
Forces are balanced (equal in size and opposite in direction)
Therefore, the body will remain at rest.
What is the size of the arrow and relationship between weight?
If reaction force is greater than weight (R>W), net force is positive.
Forces are unbalanced and acceleration in an upward direction will occur.
Origin and direction of arrow of friction?
From the point of contact and usually extending horizontally in the same direction as motion (parallel to the surfaces)
What are the components of a lever
Fulcrum
Load
Effort
What are levers
important in understanding how the body moves
What is the fulcrum
The pivot point eg a joint
What is the load
The resistance or weight being moved (eg body weight)
What is the effort?
The force applied (eg muscle contraction
What is a first class lever
The fulcrum is between the load and the effort (eg neck extension - header in football)
What is the mechanical advantage of first-class levers
If the effort arm is longer than the load arm (less effort to move a large load
What is the mechanical disadvantage of first class levers
if load arm is longer- more effort to lift a smaller load
What is a second class lever
The load is between the effort and the fulcrum (eg calf raises- ball of foot is fulcrum
Move large load with little effort
Are second class levers a mechanical advantage or disadvantage
Always advtanage
What is a third class lever
The effort is between the load and the fulcrum (most movements in the body)
Greater range of motion and speed
Are second class levers a mechanical advantage or disadvantage
Always disadvantage
What is linear motion
Movement in a straight line
What is distance
The total path traveled by a body
What is displacement
The shortest straight line distance between the start and finish points
What is speed
The rate at which an object covers distance
speed = distance / time
What is velocity
The rate of change of displacement
velocity= displacement/ time
What is acceleration
The rate at which velocitu changes
acceleration = change in velocity / time
What is momentum
The quantity of motion possessed by a moving body
momentum = mass x velocity
Calculation of weight
mass x gravitational field strength (m x g)
calculation of velocity
displacement / time
Definition of centre of mass
the point at which a body is balanced in all directions, the point from which weight appears to act
Factors affecting position of centre of mass
shape of body and
distribution of mass
What is stability?
The ability of a body to resist motion and remain at rest, or for a body to withstand a force applied and return to its original position without damage
4 factors that affect stability
1- mass of body
2- height of centre of mass
3- base of support
4-line of gravity
What are the 3 technological methods to analyse biomechanics
1- limb kinematics
2- force plates
3- wind tunnels
What is limb kinematics
Study of movement in relation to time and space
Used to film and study movement
Can help improve technique
What are force plates
A rectangular metal plate with built in transducers usually sunk into the ground
Measure ground reaction force
can be used for gait analysis
What are wind tunnels
controlled spaces for testing airflow over objects
Test aerodynamics
4 components of a lever system
lever,
fulcrum,
effort,
load
What is the effort arm
distance from effort to fulcrum
What is the load arm
the distance from the load to the fulcrum
What is a first class lever
fulcrum is in the middle
2nd class lever
load in the middle
3rd class lever
effort in the middle
Mechanical advantage of 2nd class lever
when the effort arm is greater than the load arm —— a large load can be moved with a relatively small effort
Mechanical disadvantage of a 3rd class lever
when the load arm is greater than the effort arm—— a large effort is required to move a relatively small load
What is eccentric force
A force applied outside the centre of mass, resulting in angular motion
What is torque
a measure of the turning force applied to a body
What is angular velocity
and formula
the rate of change in angular displacement
angular displacement / time taken
=radians per second(rad/s)
What is angular distance?
total angle of a body turns from start to finish when rotating about an axis
What is angular displacement
the smallest angle between the start and finish position of a body rotating about an axis
What is angular speed and formula
the rate of change angular distance
angular distance/ time taken
= radians per second
Angular acceleration/ deceleration definition and formula
The rate of change in angular velocity
(Final angualr velocity - initial angular velocity)
/
time taken
What is moment of inertia
The resistance of body to change its state of angular motion or rotation
What is an internal force
generated by the CONTRACTION of SKELETAL MUSCLE
Examples of internal force
100m- contract rectus femoris - extend
knee- drive away from blocks
What are 4 examples of EXTERNAL FORCES
WEIGHT
REACTION
FRICTION
AIR RESISTANCE
5 effects of FORCE
Create motion
accelerate
decelerate the body
changing the direction
changing the shape
What is limb kinematics
the study of movement in relation to time and space
3D or optical motion analysis records an athlete performing a sporting action.
Force plates
Ground reaction forces can be measured in laboratory conditions using force plates
Data from an athlete balancing, running or jumping on a force plate and can be used to assess the size and direction
What is reliability?
To extent to which an experiment, test or measuring procedure gives the same results after repeated trials
What is validity?
how well a test measures what it claims to measure
It is important for a test to be valid in order for the results to be accurately applied and interpreted
Negative of biomechanics tests
specialist, expensive and usually in a lab
What are wind tunnels
F1 teams spend tens of millions getting the aerodynamics of the car right
Can even use for cycle helmet
object placed inside the wind tunnel- may study the flow of air around an object
aim of wind tunnel is to improve the flow of air around an object- streamlining its path through the oncoming air and potentially increasing lift or decreasing drag
Negatives of wind tunnnels
Need specialist faciloties- housed in engineering bases
very expensive and require complex analysis
What is the fosbury flop technique
-uses a j-curve to allow greater velocity
-plants the outside foot to allow the inside leg to lift, along with the arms, at take off to raise the centre of mass as high as possible
-fully extends the spine to rotate around the bar moving the centre of mass outside the body and below the bar.
fosbury flop technique requires less force at take-off to clear the same heights as earlier techniques.
What are lever systems
the co-ordination of our bones and muscles, primarily to create human movement
functions of lever systems
to generate musclaar effort to overcome a given load
to increase the speed of a given movement3`
What is linear motion
movement of a body in straight or curved line, where all parts move the same distance, in the same direction over the same time
What is direct force
A force applied through the centre of mass resulting in linear motion
What is centre of mass
the point at which a body is balanced in all directions
What is distance
the total length covered from start to finish positions (m)
What is displacememnt
the shortest straight-line route from start to finish positions (m)
What is speed
the rate of change in distance and can be calculated using the following equation
speed = distance/time taken
(dont stop there)
What is velocity
the rate of change in displacement an d can be calculated by
velocity = displacement/ time
