Mechanical Principles: Forces, Energy, and Simple Machines
Key Mechanical Principles
Force (F) is any action that modifies the state of rest or motion of a body. It is measured in Newtons (N). A moment of a force (M) is the product of the value of the force by the distance between that point and the point of application of the force. Its unit of measurement in the SI is the Newton-meter (Nm). Work (W) done by a force is the product of the force produced by the displacement. In the SI, work is measured in Joules (J). Power (P) is the work done per unit of time. The power unit is the Watt (W), equivalent to the power required to perform work of 1 J in 1 second. (1 CV = 746 W) (1 hp = 746 W) (1 kgf · m/s = 9.8 W). Energy (E) is the ability of a system to do work, expressed as potential energy and kinetic energy. Potential energy (Ep) is the energy that a body possesses by virtue of its position or status. Yield (η) is the relationship between the energy obtained in the absorption system and is usually expressed in %. Angular Velocity (ω) is the velocity of rotation. It is measured in radians per second (rad/s) (ω = 2 × π/60 rad/s = 1 rpm). A machine is a set of mechanisms that perform a particular job. Mechanical Advantage is found by dividing the resistance of a body by the applied force (Fm).
Simple Machines
A Lever is a simple machine consisting of a rigid bar that rests on a support called a fulcrum. There are three classes of levers:
- First-class levers (inter-mobile) (e.g., pliers or scissors)
- Second-class levers (inter-resistance) (e.g., nutcracker, wheelbarrow, or paddles)
- Third-class levers (inter-power) (e.g., fishing rod or tweezers)
The law of equilibrium of the lever states that a lever is in equilibrium when the driving force (Fm) multiplied by the power arm (bp) is equal to the product of the resistance force (Fr) multiplied by the resistance arm (br) (Fm · bp = Fr · br). An Inclined Plane is a simple machine consisting of a flat surface forming an angle with the horizontal. A Wedge is a piece finished in a very acute angle. The operating principle of the wedge is the same as the inclined plane and amplifies the received forces. The mechanical advantage of the wedge indicates that for a constant head width, the longer the wedge, the lower the force that must be applied.
Other Simple Machines
A Winch is a simple machine consisting of a cylinder or drum that rotates on an axis. At one end is a handle for implementing the driving force (Fm). A Screw is a mechanical fastening device consisting primarily of a plane wrapped around a cylinder or cone. Advance (A) is the distance, parallel to the axis of the screw, that a nut moves when it is given a full turn. A Machine is a set of parts or elements, both mobile and stationary, grouped properly to utilize, direct, or regulate a form of energy, transforming it to produce a useful final effect.
Types of Machines
Prime movers transform energy obtained from fossil fuels, wind, water, steam, or electricity. Examples include general motors, turbines, and alternators. Machine operators use the energy provided by the prime movers for an immediate result. These, in turn, may harbor, modify, and transform other classes of energy.
Machine Elements
Auxiliary elements include mechanical energy storage (flywheel and elastic elements), mechanical energy dissipation (braces), and elements of friction (bearings and supports), as well as lubrication types. An accumulator is a mechanical device that can store or accumulate a certain amount of mechanical energy and return it at the right time. Well-known accumulators include the flywheel (which accumulates energy as rotational kinetic energy) and elastic elements (which store energy as elastic potential energy). A flywheel consists of a steel wheel dragged on the drive shaft, which rotates in unison with it. A typical example is the flywheel on an internal combustion engine. Elastic elements include springs. Springs are elements that are deformed by the action of a force and regain their original shape when the force ceases. Types of springs include compression springs, where the forces acting on them produce a shortening of their initial length.