Forces

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Forces

Forces

The commands in the Forces menu and Forces toolbar add, measure, and configure kinetostatic forces*. We will use the generic term Forces.

In MechDesigner, to calculate correctly the Forces that act on a Part:

the kinematic-chain that is kinematically-defined,  

a minimum of one Part in the kinematic-chain has Mass, and usually a Mass Moment of Inertia - see Mass Properties, below

the Power flows correctly through the kinematic-chain from the correct Power Source - see Configure Power Source.


* Norton calls it the “Inverse Dynamics Problem”.


Mass Properties

Parts have three sources of Mass and a Mass Moment of Inertia. The sources are:

Profile / Extrusions - see Extrusion > Mass Properties

User Mass Properties - see CAD-Line > Mass Properties tab > User Mass Properties

SolidWorks Mass Properties - see CAD-Line > Mass Properties tab > SOLIDWORKS Mass Properties

We add together the three sources of Mass Properties.


Note:

If a Part has Mass but does not have Mass Moment of Inertia, it is called a Point-Mass (or a Black Hole!). In reality, a Mass is distributed, and so the body must also have a Mass Moment of Inertia.

However, you can, if you wish, add a Point-Mass to a Part without a Mass Moment of Inertia. For very slow moving machines, or for Parts that mainly translate (rotate only a small amount), this may provide the accuracy you need.


MD-Globe-www On-line Tutorial: Tutorial 13: Forces Introduction


Force menu

 Forces menu (MD17)

 Forces menu (MD17)


Force toolbar

The Force toolbar is to the right of the graphics-area.

Forces toolbar

Forces toolbar


Buttons to Scale Force and Torque Vectors in the graphics-area.

Vector scaling F: Force Vectors, T: Torque Vectors

Vector scaling
F: Force Vectors, T: Torque Vectors

“Force Vectors” include both the Force Vectors and Torque Vectors.

If, after you display Force Vectors, the arrowheads of the vectors are outside of the graphics-area, you must use the Scale buttons to decrease the length of the Force Vectors and/or Torque Vectors - see Feedback Area > Vector Scaling buttons


Force definitions - as defined by IFTOMM  International Federation on the Theory of Machines and Mechansims :

FORCE

Action of its surroundings on a body tending to change its state of rest or motion.

LINE OF ACTION OF A FORCE

The line along which the vector that represents a given force lies.

MAGNITUDE OF A FORCE

Number of units of force obtained by comparing a given force with a standard, taken as unit force -(SI units : Newtons)

ACTIVE [APPLIED] FORCE

Force capable of producing motion.

REACTION

Force arising in a constraint and acting upon a constrained body due to the action of an active force upon that body.

CENTRIPETAL FORCE

Force causing the centripetal acceleration of a particle.

INERTIA FORCE

Product of the mass of a particle and the negative of its acceleration. Following D'Alembert, the inertia force can be regarded as being in equilibrium with the resultant of all the forces acting on the particle.

CENTRIFUGAL FORCE

Inertia force of a particle moving uniformly along a circular path.

CORIOLIS FORCE

Inertia force equal to the product of the mass of a particle and the negative of its Coriolis component of acceleration.

GRAVITATIONAL FORCE

Force equal to the product of the mass of a particle and the Gravitational Acceleration on Earth - taken as 9.806m/s/s.

tog_minusAcceleration Definitions:

We calculate for you those Forces that result from these Accelerations :