Applied and constraint forces

APPLIED AND CONSTRAINT FORCES

1. Applied Forces

• The external forces acting on a system of body from outside the system are called applied forces. In other terms, applied forces are the forces applied externally to a body. These forces may be applied with or without physical contact.

• Examples:

■ Electric, magnetic and gravitational forces are examples of forces that can be applied without actual physical contact.

■ Forces due to friction, forces due to external loads, spring forces, impact forces, etc., are examples of forces that can be applied through direct physical or mechanical contact.

• Classification of applied force: The applied forces are classified as:

(i) Active force, and

(ii) Reactive force.

(i) Active Force: The force exerted by one body on another is called active force.

(ii) Reactive force: When one body exerts force on another body, then the opposite force exerted by the second body on the first is called reactive force (or reaction).

Note 

Active and reactive forces are always equal and opposite.

2. Constraint Forces

• When two or more bodies are connected together to form a group or system, the pair of action and reaction forces between any two of the connected bodies are called constraint forces. In other words, constraint forces are the forces existing internally within the body. 

• These forces constrain the connected bodies to behave in a specified manner defined by the nature of the connection.

• In simple terms, constraint forces, also called internal forces, are those forces which hold together the particles of a bødy. And if more than one body is involved then the force which holds the two bodies together is called the constraint force.