Movements 1. Forces Flashcards
Forces
Muscle contraction
Fulcrum/axis
Joint
Levers
Limbs
Centre of gravity
sacrum
Where gravity acts
Mass of all body segments evenly distributed
Concentric
Muscle shortens and bulges is and isometric contraction
Eccenteic
Muscle lengthens and returns to original length isotonic
Isometric
Muscle under tension but not changing length
Force
And influence that changes the state of rest or motion of the body
push – compression or pull – tension
External forces:
•Gravity
•water – resistance/bouancy
• Manual/mechanical forces used by therapists – passive movements and stretches mobilisation
Law of inertia
Body will remain at rest or in a state of uniform motion unless acted upon by an external force
Weak quads reduce inertia
Law of acceleration
The acceleration of the body is parallel directly proportional to the force acting on the body Is in the same direction of the force and inversely proportional to the mass of the body
Make exercise faster
Law of action/reaction
To every action there is an equal and opposite reaction
Resistance is equal
Magnitude
Size or strength of force measured in kg lbs and Newton’s
Action line
Straight line through the point of application
Resultant force
Combination of forces
The final effect of all these forces is the resultant force.
Resultant force = is the simplest force necessary to produce the same effect as all the forces acting together
Linear force systems
To forces act along the same action line
direction of force may be an opposite direction – tension affect (Collinear force system) tug of war
Direction of force may be in same line of direction – compression affect two people moving a box
Parallel force system
Direction of forces are parallel either in the same or opposite directions
Forces are coplanar but do not share the same action line- see saw
Parallel forces in opposite directions can produce a rotatory effect – force couple
Force couple
Two parallel forces that are equal in magnitude Do not share the same line of action therefore produced a rotatory effect
Force couple – pelvic control
Forces are equal in magnitude but opposite in direction
Muscles located at different points relative to the axis act together to produce rotation
Concurrent force system
All forces act at the same point somewhere
Resultant force but on a specific line or body part rather than the whole body
Examples:
Sternal and clavicular head of pectoralis major
Stability
Stability of an object refers to the ease with which it can be displaced
Equilibrium
Equilibrium results when the forces acting on the body are perfectly balanced and the body remains at rest. Different types of equilibrium states reflect the level of stability.
Stable Equilibrium
occurs if the forces acting on a body tend to restore it to its original position following application of a displacing force. The line of gravity always remains within the base of support, even following displacement.
A low centre of gravity, and an extensive base of support with the line of gravity falling close to the centre of the base, improves the stability
Unstable Equilibrium
Little force is required to make the body topple and assume a new position. A high COG, a small BOS with the LOG falling close to the edge of the base, will mean that the LOG is easily displaced outside of the BOS
Neutral Equilibrium
occurs when following the application of a displacing force, the relationship of the centre of gravity, line of gravity and base of support all remain as before eg rolling ball, sliding across a plinth.
Line of gravity
The projection of the CoG on the ground, represented by a perpendicular line on the ground through CoG
Base of support
All forces act here all points of contact
