biomechanical principles Flashcards
newton’s first law
•law of inertia
•an object will continue in as state of constant velocity until compelled to change by an external force
newton’s second law
•law of acceleration
•an object will accelerate proportional to the force acting and in the direction of that force
• mass x acceleration = force
newton’s third law
•law of reaction
•for every action there is an equal and opposite reaction
force definition
a push or pull that tends to alter the state of motion of a body
momentum force
the amount of motion possessed by a moving body
acceleration definition
the rate of change in velocity
weight definition
the force that the earth exerts on the mass of a body
velocity definition
rate of change in displacement of the shortest route from A to B
force equation
force= mass x acceleration
momentum equation
momentum = mass x velocity
acceleration equation
acceleration = force / mass
or
acceleration = change in velocity / time
velocity equation
velocity = displacement (distance) / time
centre of mass definition
A point at which mass is distributed evenly in all directions.
factors effecting centre of mass
•distribution of mass
•movement of limbs
•uniformity if shape
centre of mass and distribution of mass
In the human body centre of mass is constantly moving depending on the distribution of the mass.
centre of mass and uniformity of object
In a uniform object (something with the same density from the centre to all parts), like a shot, the centre of mass remains in the middle at all times.
centre of mass and movements of limbs
In unique scenarios, like the Fosbury Flop on the right, the centre of mass may move outside of the physical body.
stability
a measure of how a body is moved from a position of equilibrium or balance.
line of gravity
an imaginary lie extending vertically downward to the ground from the centre of mass
base of support
the area enclosed by the points of contact with the ground.
factors effecting stability
- Low centre of mass – The lower we are to the ground and the shorter the line of gravity, the more stable we are. Think a rugby player in a tackle
- Large base of support and points of contact with the ground – The bigger the base of support the more stable we are. Think of a headstand compared to a handstand.
- Large mass – The larger our mass the larger our stability. Try shifting a heavy object off a plateau compared to a lighter one
- Line of gravity in the middle of base of support – Again consider a handstand, as soon as you lean you legs one way or the other you are likely to be unstable.
balanced forces
When two or more forces acting on a body are equal in size but opposite in direction. All forces cancel out .
unbalanced forces
When two or more forces acting on the body do no cancel out. This means a net force acts.
net force
The overall force acting on a body when all forces are considered. Also know as the resultant force.
vertical forces
• weight - acts down from the centre of mass
• ground reaction force - acts upwards from the points of contact with the ground, in reaction to all downwards forces.
horizontal forces
•friction - opposes the sliding motion of one surface across another
•Air Resistance – acts against the direction of motion, opposing the movement of the body through the air
factors affecting friction
•Characteristics/roughness of surface of sole of footwear
•Characteristics/roughness of playing surface
•Weight/normal ground reaction force (the force pushing the two surfaces together)
•Temperature - heated tyres increase friction between the rubber and the track
factors affecting air resistance
•Velocity
•Frontal cross-sectional area
•Streamlining and shape
•Surface characteristics
•Mass
friction and air resistance
•If the athlete is moving forwards the Friction must be bigger than the Air Resistance
•If Air Resistance is bigger than Friction it means they will be decelerating, but direction of motion will still be forwards
•If the athlete is standing still there won’t be horizontal forces acting on them
weight and reaction
If the athlete isn’t moving up or down the Weight and Reaction forces should be the same length
class 1 lever system
• fulcrum
class 1 lever example
• elbow extension
• neck movement
class 1 mechanical advantage / disadvantage
dependent of where the fulcrum sits
class 2 lever system
• load/resistance
class 2 lever example
planter flexion
class 2 lever advantage/disadvantage
longer effort arm
- this mean there is less effort needed to move a heavy load
however: lack ROM and speed
class 3 lever system
• effort
class 3 lever example
any movements
other than ankle and elbow extension
class 3 lever advantage/disadvantage
this means you have more ROM and speed
however: means heavy loads need a lot of effort
methods of technology in improving technique
• limb kinematics
• force plates
• wind tunnels
limb kinetics
• produces 2D moving model of movement
• shows technical performance
• maps joint movement
• all movement can be graphed and analysed
force plates
• measured ground reaction force
• gain quantities of balance and gait
• measure vertical and horizontal force
• combines with limb kinematics
wind tunnels
• measures aerodynamics
• pressure sensors
• tubular passage
