2.3
Introduction to force
Consider water flowing from a nozzle to a turbine vane. As the water hits the turbine vane, it exerts a force that causes it to move along the flow of…
When a man pulls or pushes a box, it moves in a horizontal direction. The pull or push exerted on the box that results in its motion is known as force. It is a vector quantity expressed in newton.
Forces acting on bodies can be categorized as external and internal forces. When the force applied externally on a body creates an effect, it is termed an external force, while the reaction forces existing inside the body are known as internal forces.
The principle of transmissibility states that if the point of application of a force on a body changes but remains in the same line of action, the resultant force on the body does not change.
Consider two forces acting on a rigid body. According to the principle of transmissibility, the body remains unchanged if the forces acting on the body are in the same line of action, even while acting at different points.
Since these forces are equal and opposite, their sum equals zero, and the resultant force on the body remains unchanged.
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Q1: What is force and how is it measured?
Force is an impact that changes an object's motion, shape, or orientation. It is a vector quantity with both magnitude and direction, measured in newtons (N) in the SI unit system. For example, an object with a mass of 1 kg accelerating at 1 m/s² experiences a force of 1 N. Forces can result from physical contact, such as pushing or pulling, or non-contact interactions like magnetic or gravitational forces.
Q2: What is the difference between external and internal forces?
External forces are applied to a body from outside and create reactive forces on its surroundings, such as body weight or friction. Internal forces are reaction forces existing within the body material itself. When an external force acts on a bracket, for example, the external effects are reactive forces from the foundation and bolts, while internal effects are the resulting stresses and deformations distributed throughout the material.
Q3: What does the principle of transmissibility state?
The principle of transmissibility states that if a force's point of application changes but remains on the same line of action, the resultant force on a rigid body remains unchanged. Two equal forces acting from different points on the same line of action produce the same effect as a single force. This principle is fundamental to understanding how forces affect rigid bodies in mechanics.
Q4: How do forces cause motion in objects?
When a force is applied to an object through pushing or pulling, it causes the object to move. For instance, when water from a nozzle hits a turbine vane, it exerts a force that causes the vane to move along the flow direction. The magnitude and direction of the applied force determine how the object's motion, shape, or orientation changes.
Q5: Why is force considered a vector quantity?
Force is a vector quantity because it has both magnitude and direction. Simply knowing the strength of a force is insufficient; the direction in which it acts is equally important for predicting an object's response. This dual nature makes force fundamentally different from scalar quantities, which have only magnitude, and is essential for analyzing complex force systems.
Q6: What are internal stresses and deformations in a loaded body?
Internal stresses and deformations are the internal effects that occur within a material when external forces are applied. These effects depend on the material properties and geometries of the body. For example, when a bracket experiences an external force, internal stresses and deformations develop throughout its material, distributed according to how the material responds to the applied load.
Q7: How does the line of action affect force equivalence?
The line of action is the path along which a force acts on a body. According to the principle of transmissibility, forces acting on the same line of action are equivalent regardless of where they are applied, as long as they have equal magnitude and direction. This concept simplifies force analysis by allowing forces to be repositioned along their line of action without changing their effect on a rigid body.