Chapter 6. Basic Mechanical Principles

Force, work, energy and power. Force is measured in newtons (N). Work = force × distance (joules). Power = work / time (watts). Energy is the capacity to do work [8][11].

Simple machines: lever, wheel and axle, pulley, inclined plane, wedge and screw. They make work easier by changing the size or direction of a force.

Mechanical advantage (MA) = load / effort. For a lever, MA = effort arm / load arm.

Machines never create energy; the work put in is at least equal to the work done.

Torque is the turning effect of a force: torque = force × perpendicular distance from the pivot (N·m). Tighten fasteners to the specified torque to avoid damage [8][11].

Gears, belts and chains transmit motion and power. Gear ratio = number of teeth on driven gear / number of teeth on driving gear. A larger driven gear gives more torque and less speed.

Friction resists motion and causes wear and heat; lubricants (oil, grease) reduce it. Bearings support rotating shafts.

Fluid power. Pressure = force / area. In hydraulics, pressure applied to a confined liquid is transmitted equally in all directions (Pascal’s law), so a small force on a small piston can lift a large load on a large piston. Pneumatic systems use compressed air [8][11].

Heat and thermal expansion. Materials expand when heated; allow for this in pipes, rails and structures.

Maintenance basics. Lubricate, tighten, align, clean and replace worn parts according to a schedule.

Review: A lever has an effort arm of 2 m and a load arm of 0.5 m. What effort lifts a 200 N load? (Answer: MA = 4, so effort = 200 / 4 = 50 N.)