Biophysics (Mechanics)

Joints have a max degree of movement/freedom, displacement and max rotation capacity, what is this maximum?

- max 3 degrees of displacement

- max 3 degrees of rotation

What is the normal degree of movement/freedom (displacement), and rotation capacity for a joint?

- no displacement

- 1 to 2 rotations

how do muscles contract

muscles can only produce a pulling force, a force of contraction in the direction of its fibers (from insertion to origin)

if Fj (force that appears at the joint) is large then...

the ligament can be stressed or torn (sprain)

if Fm (muscular force) is large then....

the muscles and tendons can tear (strain)

if Fl (load on the system) is huge then:

the bones can also break

the magnitude of the torque force (momentum) formula is:

Newton * meters

(fuerza por distancia)

clockwise torque

-

anticlockwise torque

+

If the angle between two products is 0 the vectorial product is

Zero

Torque

A force applied to rotate an object around an axis provoking an angular acceleration.

It is the vectorial product of distance and force

A body in equilibrium the result of forces acting on it is ________________ (no linear movement) and the result of angles acting on it is _______________ (no rotation)

Zero, Zero

A force will produce a ______________________ motion and a torque will produce an __________________ motion

linear, rotation

If the torque produces a rotation Clock Wise is defined as _____________________ while if it is Counter Clock Wise is defined as ___________

Negative Positive

Model of an arm

The sum of forces and the sum of torques must be zero in equilibrium

A weight of mass M kg does a force of

F = M x g (g = 9,8 m/s²)

A person extends his/her forearm (the elbow joint). That means that

3. There is rotation movement then there is a torque, but there is no up and down move of the arm parallel to the ground, so no forces.

3 multiple choice options

The figure schematically represents an extremely simplified model of the shoulder joint, where we assume

that the only active muscle is the deltoid (as indicated). The force F1 represents the weight of the arm. The

force exerted by the joint will point:

1. downwards and rightwards

2. downwards and leftwards

3. upwards and rightwards

4. upwards and leftwards

Downwards and rightwards. According to the 3rd law of newton the shoulder joint force will have a reaction force in the opposite direction

For any joint the minimum 3 forces to be the system in equilibrium are

. Load on the system (FL)

. Muscular Force (FM)

. Force that appears at the joints (FA)

Force joint is a _______________ force to the muscle force. The direction will be __________________ to it

reaction opposite

The reaction force value will depend on

. Load

. Distance to the joint

. Orientation

Excessive reaction force in a joint may produce in the ligaments

stress and torn (sprain)

High force in the muscle in response to a heavy load may result in the muscles in

tearing muscles and tendons (strain)

High loads in the bones may produce

broken bones

The longer the distance of a load to the joint, the muscle force needed to reach the equilibrium will be

higher