Week 10 - Principles of movement, force systems and lever orders Flashcards
What are the fundamentals to movement analysis?
→ Movements occur in planes and around axis
→ Movement (motion) is governed by forces
→ Forces can be balanced or unbalanced
→ Balanced forced result in NO movement
→ Unbalanced forces result in movement (acceleration)
→ Forces have to obey rules
What is a body?
Can be as a whole, or as individual parts which make up a wider body.
A whole body as well as individual segments have their own centre of mass and centre of gravity.
What is centre of mass?
Average position of the mass of an object (relates to the mass of an object).
What is centre of gravity?
The point where gravity appears to act (refers to the force of gravity).
What is the line of gravity?
The effect of gravity and how it effects the centre of gravity.
Vertical line passing from COG of an object to the ground.
What are the 3 types of force?
→ Gravitational - weight
→ Applied - contact
→ Inertial - motion
What is force?
A vector - it has a magnitude and direction.
It also has a point of application and a line of action.Force is measured in newtons.
What is load?
The force exerted on a surface/body
What is Newtons 1st law of motion?
Concerned with balanced forces.
→ States that if a body is at rest and the forces acting on it are balanced then the body will remain at rest
→ However if the body is moving and the forces acting are balanced then the body will keep moving at constant speed in a straight line
e.g. stationary box, leg when sat down in chair for long period
What is Newtons 2nd law of motion?
Concerned with unbalanced forces - unbalanced forces produce acceleration.
→ The bigger the unbalanced force the bigger the acceleration.
Force = MASS X ACCELERATION
(F= ma)
Acceleration is proportional to the unbalanced force acting on it.
What is Newtons 3rd law of motion?
Concerns equal and opposite forces.
“If A exerts a force on B, then B exerts an equal but opposite force on A”
For every action there is an equal and opposite reaction.
What is the equation for acceleration?
ACCELERATION = FORCE/MASS
Force inversely proportional to mass acting on it).
A heavier object will require more force to accelerate it compared to an object of a smaller mass.
What is the ground reaction force vector?
The opposing force offered by the ground.
What is a lever?
A rigid bar (body segment) which rotates around a fulcrum (joint axis)
The rotation is produced by an unbalanced force (generated by muscle contraction in some cases) applied to the lever.
The human body is a complex system of levers that work in 3 dimensions.
What is a moment?
Turning effect a force has around a point measured in (Newton Meters) NM.
(sometimes referred to as a torque)
The moment is dependent upon the size of the force and the moment arm i.e. how far the force is applied from the turning point
What is the equation of a moment?
force x distance
What is the resultant force?
final effect of multiple forces
What is a co-planar force system?
When the lines of action of set forces lie in a single plane.
→ Direction of forces are parallel in either the same or opposite directions
→ In the same plane (co-planar) but do not share the same action line
→Parallel forces in opposite direction can produce reciprocal rotary effect ‘FORCE COUPLE’.
What are collinear force systems?
When the lines of action of all the forces of a system act along the same line.
e.g. tug of war, rugby scrum, pushing weight along ground
What is a concurrent force system?
All forces act on the same point
e.g. muscles of multiple compartments with multiple lines of action and the subsequent resultant force.
What is a first order lever?
Fulcrum is placed between the effort (force) and the resistance load
What is a second order lever?
The resistance (load) always lies between the fulcrum and the force
What is a third order lever?
The effort or force is always placed between the fulcrum and resistance.
Anatomical examples of first order lever?
The head/neck
Hips - step through gait → fulcrum is hip joint , effort is glut med. , load is weight of body on contralateral side.
Gravity and weight of limb cause adductor moment at hip joint - so internal abduction is needed to stop hip from dropping.
Anatomical examples of second order lever?
The action of the calf muscle during the push off when walking/running
fulcrum = axis of the MT/P joints, resistance = body weight,
effort = produced by the calf muscles
Anatomical examples of third order lever?
The action of the muscles in upper arm to lift a weight at the elbow.
fulcrum - elbow joint
resistance - weight of forearm or weight in hand
effort - biceps
When does mechanical advantage occur?
→When the lever arm is longer as larger movement is generated for a given force .
→Efficiency depends on where the forces are located in relation to the fulcrum.
→ Ma >=1 longer than resistance arm - force advantage
