Biomechanics 05 (Torque + Moment)

Torque

turning effect produced by a force

Torque is also known as the “moment of force” or “moment”

True

Centric force

Force line of action directed through center of gravity

Eccentric force

Force line of action not directed through center of gravity

Force couple

2 eccentric noncolinear forces, equal and opposite in direction

Centric Force causes changes in __

translation only

Eccentric Force causes changes in __

translation and rotation

Force couple causes changes in __

rotation only

What is the moment arm of a force?

perpendicular distance between the line of action of a force and the axis of rotation

Longer moment arm

increases turning effect of a force

Shorter moment arm

decreases turning effect of a force

What equation represents Torque (T)?

T = F * r

If force is measured in newtons (N) and moment arm is measured in meters (m), what are the units for Torque?

N * m

Counterclockwise represents __ torque, and Clockwise represents _ torque

Positive / Negative

Muscle force creates torque at a specific joint (since muscles cross joints)

True

Muscle moment arm length does not change as a joint rotates

False

As your elbow is extended, the moment arm will get shorter.

True

What is the relation of muscle torque to resistance torque?

It opposes resistance torque

In static equilibrium, what is true of external forces and torques?

External torques and forces must sum to zero

Clockwise torque will not be canceled out by counterclockwise torque

False

Center of Gravity (cg)

The point where the entire mass of a body may be assumed to be concentrated

Center of Gravity (cg) changes when parts of an object change position. It’s not a fixed point + is imaginary in space

True

Location of the cg does not depend on location of each limb

False

Lift left arm away from side

cg shifts to the left

Lift left arm in front of body

cg shifts forward

Raise both arms away from side

cg shifts upward

cg height is what percentage of standing height?

55% (female) to 57% (male)

When the body is a projectile, what path is followed by its center of gravity (cg)?

fixed parabolic

Body segments do not rotate around the fixed path of cg

False

Stability

capacity of a body to return to equilibrium when displaced

The following are factors affecting stability

All of the above

The Lower, wider, heavier you are, the more stable you are

True