Week 10 - Principles of movement, force systems and lever orders

Question 1

What are the fundamentals to movement analysis?

Answer 1

→ 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

Question 2

What is a body?

Answer 2

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.

Question 3

What is centre of mass?

Answer 3

Average position of the mass of an object (relates to the mass of an object).

Question 4

What is centre of gravity?

Answer 4

The point where gravity appears to act (refers to the force of gravity).

Question 5

What is the line of gravity?

Answer 5

The effect of gravity and how it effects the centre of gravity.

Vertical line passing from COG of an object to the ground.

Question 6

What are the 3 types of force?

Answer 6

→ Gravitational - weight
→ Applied - contact
→ Inertial - motion

Question 7

What is force?

Answer 7

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.

Question 8

What is load?

Answer 8

The force exerted on a surface/body

Question 9

What is Newtons 1st law of motion?

Answer 9

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

Question 10

What is Newtons 2nd law of motion?

Answer 10

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.

Question 11

What is Newtons 3rd law of motion?

Answer 11

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.

Question 12

What is the equation for acceleration?

Answer 12

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.

Question 13

What is the ground reaction force vector?

Answer 13

The opposing force offered by the ground.

Question 14

What is a lever?

Answer 14

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.

Question 15

What is a moment?

Answer 15

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

Question 16

What is the equation of a moment?

Answer 16

force x distance

Question 17

What is the resultant force?

Answer 17

final effect of multiple forces

Question 18

What is a co-planar force system?

Answer 18

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’.

Question 19

What are collinear force systems?

Answer 19

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

Question 20

What is a concurrent force system?

Answer 20

All forces act on the same point
e.g. muscles of multiple compartments with multiple lines of action and the subsequent resultant force.

Question 21

What is a first order lever?

Answer 21

Fulcrum is placed between the effort (force) and the resistance load

Question 22

What is a second order lever?

Answer 22

The resistance (load) always lies between the fulcrum and the force

Question 23

What is a third order lever?

Answer 23

The effort or force is always placed between the fulcrum and resistance.

Question 24

Anatomical examples of first order lever?

Answer 24

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.

Question 25

Anatomical examples of second order lever?

Answer 25

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

Question 26

Anatomical examples of third order lever?

Answer 26

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

Question 27

When does mechanical advantage occur?

Answer 27

→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