Mechanical Actions-Forces
Definition
Characteristics
Effects of a force
Representation
A force is a mechanical action exerted by a body on another body, it is known by its effects.
a) It sets a body into motion.
b) lt modifies its motion by changing its direction speed or stopping the motion.
c) It deforms the shape of a body.
A Force F is characterized by the following
point of application: it is a point where the force acts
line of action: the straight line where F acts
direction: the direction according to which the force acts
magnitude: the value or the module of the force
(S.I unit N → in Newtons)
(measured by a spring balance or dynamometer).
A force is represented by a vector F To draw it
a convenient scale must be chosen
scale varies from one representation to another.
Classification of forces
Contact forces: can not attract a body from a distance, it has to be in direct contact
Forces acting from a distance: force that can attract a body at a certain distance
3 types of forces acting from a distance
Gravitational forces
Magnetic Forces
(weights)
Electrostatic forces
(forces that come from electrifications)
Particular Forces
Weight (W): the weight is a force exerted by the Earth on an object.
Line of action: Vertical
Direction : downwards
Point of application : Center of gravity of the object
magnitude : W{N) = M(kg) × g(N/kg)
Tension
It is a force exerted by a string, chain , or spring on the object in order to hold it.
Line of action : through (along) the string
Direction: From the object to the string
Point of application : the contact between the object and the string
Magnitude: T=?
Normal Reaction
It is a force exerted by a support on the object in order to hold it
Line of action: always perpendicular to the support