Understanding Mechanical Properties and Forces
Mechanical Properties and Forces
A force is an interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity (which includes beginning motion from a state of rest), i.e., to accelerate. Force can also be described intuitively as a push or a pull. The unit of force in the International System of Units (SI) is the Newton (N). Forces are represented with arrows to indicate direction and magnitude.
Mechanical Properties of Materials
Mechanical properties determine the behavior of materials under applied forces. Key properties include:
- Resistance: The ability of a material to resist forces without excessive deformation or breaking.
- Toughness and Fragility: Toughness is the property of some materials to withstand repeated forces without breaking. The opposite property is fragility. A material like glass, which breaks easily upon impact or bending, is considered brittle.
- Elasticity: The ability of a material to recover its original shape after a deforming force is removed. There is a limit to this, called the elastic limit, beyond which the deformation becomes permanent and can even lead to breakage.
- Plasticity: The ability of a solid material to undergo permanent deformation without breaking.
- Ductility: The property of certain materials to deform permanently into thin wires without breaking.
- Malleability: The property of certain materials to deform permanently into thin sheets without breaking.
- Hardness: A measure of a material’s resistance to being scratched or penetrated.
Types of Efforts
When a force is applied to a body, we say that the body is subjected to an effort. The resistance of an object to an effort depends on three factors: size, shape, and the type of effort. There are five main types of efforts:
- Traction Effort: Occurs when two opposing forces act on a body, tending to stretch or lengthen it. Bodies subjected to traction can be flexible but should not be too elastic.
- Compression Effort: Occurs when forces acting on an object are in the same direction but opposite, tending to crush or shorten it. To support compression, a body should be rigid and preferably not very wide or long.
- Buckling: The deformation experienced by bodies subjected to compression when they are long and thin.
- Bending Stress: Occurs when forces acting on a piece are applied against its longitudinal axis, tending to bend it.
- Torque: The effect of forces that cause a body to twist or warp. The thicker the body, the more resistant it is to torque.
- Shear Stress: Occurs when two opposing forces act on the same part of an element. If the forces are large enough to overcome the material’s resistance, the result is a cut.