# Mechanical Power Variables 202

"Mechanical Power Variables" covers the changeable aspects of mechanical power. Basic power variables include speed, power, torque, horsepower, and mechanical forces. All machines rely on rotary motion, linear motion, or a combination of the two to perform work, and different power variables relate to each type of motion. Effectively converting one form of motion to another requires a clear understanding of the functional and mathematical relationship between the two forms.

Machine operators and maintenance personnel must often determine which power components are most suitable for specific operations, evaluate machine efficiency, and determine when machine components should be replaced. Familiarity with power variables and their effects can help to prevent machine downtime and component failure. After taking this class, users will understand the basic variables involved in power transmission so that they can use mechanical power properly, safely, and efficiently.

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## Class Details

Class Name:
Mechanical Power Variables 202
Difficulty:
Intermediate
Number of Lessons:
18

## Class Outline

• Mechanical Power Variables
• Force
• Work
• Power
• Work and Power Calculations
• Review: Force, Work, and Power Specifications
• Linear and Rotary Speed
• Torque
• Thrust
• Peak Torque and Power Levels
• Rotary Power Calculations
• Torque Calculations
• Review: Torque, Thrust, Horsepower, and RPM
• Friction
• Heat and Lubrication
• Tension
• Mechanical Efficiency
• Review: Friction, Tension, Lubrication, and Mechanical Efficiency

## Objectives

• Describe the importance of machine specifications.
• Describe mechanical forces.
• Describe work.
• Describe power.
• Describe work. Describe power.
• Distinguish between rotary and linear motion speed variables.
• Explain how to calculate torque.
• Describe thrust.
• Explain the functions of peak torque and power.
• Explain how rotary power is calculated.
• Explain how to use power and speed to calculate torque.
• Describe friction.
• Describe the relationship between friction, heat, and lubrication.
• Describe how tension relates to power transmission.
• Explain the concept of mechanical efficiency.

## Glossary

Vocabulary Term Definition
asperities Microscopic peaks found on all surfaces. Contact between asperities causes friction.
belt drive A mechanical system consisting of a flexible belt and at least two fixed pulleys that are used to transmit motion. Belt drive systems apply force over distance to accomplish work.
centimeters per minute cpm. A metric system unit of measurement for linear speed. Centimeters per minute is often used to indicate linear speed in machine specifications that use metric values.
composition The material makeup of an object. Composition affects the mechanical and physical properties of an object, including its ability to reduce friction.
constant A fixed number in an equation used to determine unknown variables. A constant is required to determine unknown torque and power values of rotary machine components at different levels of rpm.
contact forces Force created by physical contact between mechanical components. Contact forces, or mechanical forces, produce motion in mechanical systems.
drill A machine tool that uses rotary motion to create holes in a workpiece. Drills can be classified by their rotational speed, torque, power, and other specs.
driven component The device in a power transmission system that receives energy from a drive component connected to a power source. Driven components are typically connected to an output device that performs work.
electromagnetism A force of attraction between certain types of metals or objects charged with electricity. Electromagnetism is produced by an electric current.
English system A standard system of measurements based on the inch, pound, and Fahrenheit degrees. English system measurements are primarily used in the United States and England.
foot-pound ft-lb. An English system unit of measurement for work. Foot-pound indicates the amount of work needed to move one pound a distance of one foot.
foot-pounds per minute ft-lb/min. An English system unit of measurement for work accomplished in one minute. 33,000 foot-pounds per minute equals one horsepower.
force A push or pull that changes an object's motion or state of rest. Forces have specific directions and magnitudes.
formulas An equation used to represent the relationship between specific mathematical values. Formulas can be used to determine various input and output variables for mechanical components.
friction A force that resists motion between two components that are in contact with each other. Friction can be either static or kinetic.
ft-lb. Foot-pound. An English system unit of measurement for work. Ft-lb. indicates the amount of energy needed to move one pound a distance of one foot.
gear trains A system of gears used to transmit rotary motion from one part of a mechanical system to another. Gear trains can alter the speed, torque, and direction of energy in a mechanical system.
gravity A naturally occurring, non-contact force that pulls objects toward the earth. Gravity gives weight to loads that must be moved by machine components in mechanical systems.
grinding wheel A disc made of a bonded abrasive used to remove material from a workpiece surface. A grinding wheel rotates and shears away microscopic chips of material and can produce very fine surface finishes.
horsepower hp. A unit of power used to describe machine strength. One horsepower, or mechanical horsepower, equals 33,000 foot-pound (ft-lb.) of work per minute, or 746 watts.
hp Horsepower. A unit of power used to describe machine strength. One hp equals 33,000 foot-pound (ft-lb.) of work per minute, or 746 watts.
inches per minute ipm. An English system unit of measurement for linear speed. Inches per minute is commonly used to indicate linear speed in machine specifications.
kinetic friction Friction between objects in motion. Kinetic friction is generally less than static friction.
lb.-ft. Pound-feet. An English unit of measurement for torque. Lb.-ft. is calculated by multiplying pound-force by the distance from the rotational axis.
linear motion Motion that takes place along a straight line. Mechanical energy can take the form of rotary or linear motion.
linear speed The rate at which an object travels along a straight path. Linear speed is often expressed as inches per minute or centimeters per minute.
load The opposition to applied force in a mechanical system. Load is a value that often describes the amount of weight being carried or moved by a machine.
load The opposition to applied force in a mechanical system. Weight being carried or moved is an example of a load.
lubricant A substance used to reduce friction between two surfaces in relative motion. Oil and grease are common industrial lubricants.
maximum operating speed A machine specification that indicates the highest speed at which the machine can safely operate. Maximum operating speeds for machines may be expressed in inches per minute, centimeters per minute, or revolutions per minute.
mechanical efficiency A measure of the work output of a system versus the total energy input. An efficient system is able to convert a greater amount of the supplied energy into the intended useful work.
mechanical forces Force created by physical contact between mechanical components. Mechanical forces, or contact forces, produce motion in mechanical systems.
mechanical power variables The properties of mechanical energy that vary for specific machines and applications. Speed, torque, and horsepower are the three main mechanical power variables for mechanical systems.
metric system A standard system of measurement based on the gram, liter, and meter. Metric system measurements are widely recognized as standard internationally.
motion A change in an object's position as a result of force. Motion is created in mechanical systems by contact forces.
newton-meter Nm. A metric system unit of measurement for work. Newton-meter indicates the amount of work accomplished by one newton over a distance of one meter.
newton-meters per second Nm/s. A metric system unit of measurement for work accomplished in one minute. One newton-meter per second equals one watt.
newtons N. A metric system unit of measurement for force. One newton is equivalent to the amount of force required to accelerate one kilogram of mass at a rate of one meter per second squared.
Nm Newton-meter. A metric system unit of measurement for work. Nm indicates the amount of work accomplished by one newton over a distance of one meter.
non-contact forces Force created without physical contact between components. Non-contact forces must be overcome by machine components in mechanical systems.
peak horsepower The maximum horsepower a machine can exert, achieved at a certain rpm. After horsepower peaks, it will decrease with increasing rpm.
peak power ratings A machine specification that indicates how much horsepower the machine can produce. Horsepower ratings are often used to classify engines, chain drives, and other mechanical components.
peak torque The maximum torque a machine can exert, achieved at a certain rpm. After torque peaks, it will decrease with increasing rpm.
pound-feet lb.-ft. An English unit of measurement for torque. Pound-feet is calculated by multiplying pound-force by the distance from the rotational axis
pound-force lb. f. An English system unit of measurement for force. One pound-force is the amount of force necessary to accelerate an object weighing 32.17 pounds at a rate of one foot per second squared.
power The rate at which a machine accomplishes work in a specified period of time. Power is equal to the amount of work accomplished divided by the time it takes to do the work.
power transmission components A device that facilitates the transfer of energy from a power source to an output device that performs work. Common power transmission components in mechanical systems include gear trains, belt drives, and chain drives.
press brake A machine tool that moves up and down to bend and shape sheet metal. The press brake is used to form metal into parts for various components.
ram The main upper portion of a press brake that slides up and down within the press frame during operation. The ram receives energy from a prime mover through power transmission components.
revolutions per minute rpm. A unit of measurement that indicates the number of revolutions a machine component makes in one minute. Revolutions per minute is used in both the English and metric systems to express rotary speed.
roller chains The most common type of chain used in industry. A roller chain consists of links, fastened together by pins, that mesh with teeth in a sprocket to transfer motion.
rotary speed The rate at which an object rotates around its axis. Rotary speed is commonly expressed as rpm, or revolutions per minute.
rotational axis An imaginary straight line passing through the center of an object. A round component such as a gear typically rotates around its rotational axis.
rpm Revolutions per minute. A unit of measurement that indicates the number of revolutions a machine component makes in one minute. Rpm is used in both the English and metric systems to express rotary speed.
specifications A description of the essential physical and technical properties of a machine or device. Specifications are also called specs.
specs A description of the essential physical and technical properties of a machine or device. Specs are also called specifications.
speed The rate at which an object moves. Speed is used to measure both linear and rotational movement.
sprockets A gear or wheel with metal teeth that meshes with the links of a chain. Sprockets are used in chain drive systems to transmit motion.
static friction Friction between two objects in contact that are not moving. Static friction is generally greater than kinetic friction and must be overcome before an object can be set in motion.
Teflon A proprietary solid lubricant used to coat surfaces. Teflon is commonly used to reduce friction between two moving components.
tension A pulling force that is directed away from the object and attempts to move, stretch, or elongate the object. Belt drive systems must operate under proper tension to transfer power effectively.
thrust A force that occurs when an object accelerates in one linear direction. Thrust can be measured in pound-force or newtons.
thrust rating A machine specification that indicates the maximum amount of thrust a machine component can produce. Machines with higher thrust ratings can move heavier loads.
torque A force that causes rotation. Torque is often measured in pound-feet.
W Watts. A metric system unit measurement for power. 746 W equals one horsepower.
watts W. A metric system unit measurement for power. 746 watts equal one horsepower.
work The result of a force applied to an object and the distance through which the force is applied. Work is equivalent to force multiplied by distance.
wrench A hand tool that tightens and turns bolts and nuts. A wrench produces torque when the operator applies force to the handle.