How Mass and ForceWork

Terms such as mass, force, torque, work, power, and energy are frequently encountered around the industrial plant. This month's column, along with the next two, will take a look at what these terms mean and "how they work." What is mass? Generally, mass is defined as the measure of how much matter an object or body contains — in other words, the total number of subatomic particles (elect...

07/01/2001


Terms such as mass, force, torque, work, power, and energy are frequently encountered around the industrial plant. This month's column, along with the next two, will take a look at what these terms mean and "how they work."

What is mass?

Generally, mass is defined as the measure of how much matter an object or body contains — in other words, the total number of subatomic particles (electrons, protons, and neutrons) in the object. If you multiply your body mass by the pull of the Earth's gravity, you get your weight.

It is important to understand that mass is independent of your position in space. The body's mass on the moon is the same as on the Earth because the number of atoms is the same. The earth's gravitational pull, on the other hand, decreases as you move farther away. Therefore, you can lose weight by changing your elevation, but the mass remains the same.

Mass is important for calculating how fast objects accelerate when force is applied to them.

What is force?

One type of force commonly recognized is weight, which is the amount of force the Earth exerts on you. There are two interesting facts about this force.

  • It pulls you down, or more exactly, towards the center of the earth.

  • It is proportional to mass. If you have more mass, the earth exerts a greater force on you.

    • When stepping on the bathroom scale, a force is exerted on the scale. This force compresses a spring, which moves the needle. When you throw a baseball, force is applied to the ball, which makes it speed up. An airplane engine creates a force, which pushes it through the air.

      Force causes acceleration. If force is applied to a toy car by pushing it by hand, it starts to move.

      The movement of the car is governed by Isaac Newton's Second Law, which forms the foundation for classical mechanics. Newton's Second Law states that the acceleration (a) of an object is directly proportional to the force (F) applied, and inversely proportional to the object's mass (m) . Therefore, the more force applied to an object, the greater the rate of acceleration; and the more mass the object has, the lower the rate of acceleration. Newton's second law is usually summarized in equation form:

      a = F/m or F = ma .

      To honor Newton's achievement, the standard unit of force in the SI system was named the newton. One newton (N) of force is enough to accelerate one kilogram (kg) of mass at a rate of one meter per second, per second (m/sec2).

      In fact, this relationship is really how force and mass are defined. A kilogram is the amount of weight at which 1 N of force will accelerate at a rate of 1 m/sec2. In English units, a slug is the amount of mass that 1 lb of force will accelerate at 1 ft/sec2, and a pound mass is the amount of mass that 1 lb of force will accelerate at 32 ft/sec2.

      The Earth exerts enough force to accelerate dropped objects at a rate of 9.8 m/sec2, or 32 ft/sec2. This gravity force is often referred to as g in equations. If you drop an object off a cliff, for each second it falls, it speeds up by 9.8 m/sec2. If the object falls for 5 sec, it reaches a speed of 49 m/sec. If a car accelerated at this same speed, it would reach 60 mph in less than 3 sec!

      Usually, when talking about forces, there is more than one involved, and they are applied in different directions. Consider a car sitting still. Gravity exerts a downward force everywhere on the car, while the ground exerts an equal and opposite upward force on the tires. Therefore, the car does not move.

      When the car begins to accelerate, some new forces come in to play. The drive wheels exert a force against the ground in a horizontal direction that makes the car start to accelerate. When moving slowly, almost all of the force goes into accelerating the car. The car resists acceleration with a force equal to its mass multiplied by its acceleration. Force starts out large because the car accelerates rapidly at first. As it begins to move, air exerts a force against the car, which grows larger as the car gains speed. Aerodynamic drag force acts in the opposite direction of the force of the tires, which is propelling the car, so it subtracts from that force, leaving less force available for acceleration.



      Common units of mass and force

      1000 gram (g) = 1 kilogram (kg)

      = 2.205 pounds mass (lbm)

      1 lbm = 0.4536 kg

      1 slug = 14.5939 kg = 32.17 lbm

      1 lb force (lbf) = 4.448 Newton (N) = 4.448 joules/meter

       



Top Plant
The Top Plant program honors outstanding manufacturing facilities in North America.
Product of the Year
The Product of the Year program recognizes products newly released in the manufacturing industries.
System Integrator of the Year
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
September 2018
2018 Engineering Leaders under 40, Women in Engineering, Six ways to reduce waste in manufacturing, and Four robot implementation challenges.
July/Aug
GAMS preview, 2018 Mid-Year Report, EAM and Safety
June 2018
2018 Lubrication Guide, Motor and maintenance management, Control system migration
August 2018
SCADA standardization, capital expenditures, data-driven drilling and execution
June 2018
Machine learning, produced water benefits, programming cavity pumps
April 2018
ROVs, rigs, and the real time; wellsite valve manifolds; AI on a chip; analytics use for pipelines
Spring 2018
Burners for heat-treating furnaces, CHP, dryers, gas humidification, and more
August 2018
Choosing an automation controller, Lean manufacturing
September 2018
Effective process analytics; Four reasons why LTE networks are not IIoT ready

Annual Salary Survey

After two years of economic concerns, manufacturing leaders once again have homed in on the single biggest issue facing their operations:

It's the workers—or more specifically, the lack of workers.

The 2017 Plant Engineering Salary Survey looks at not just what plant managers make, but what they think. As they look across their plants today, plant managers say they don’t have the operational depth to take on the new technologies and new challenges of global manufacturing.

Read more: 2017 Salary Survey

The Maintenance and Reliability Coach's blog
Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
One Voice for Manufacturing
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Maintenance and Reliability Professionals Blog
The Society for Maintenance and Reliability Professionals an organization devoted...
Machine Safety
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
Research Analyst Blog
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Marshall on Maintenance
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
Lachance on CMMS
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Material Handling
This digital report explains how everything from conveyors and robots to automatic picking systems and digital orders have evolved to keep pace with the speed of change in the supply chain.
Electrical Safety Update
This digital report explains how plant engineers need to take greater care when it comes to electrical safety incidents on the plant floor.
IIoT: Machines, Equipment, & Asset Management
Articles in this digital report highlight technologies that enable Industrial Internet of Things, IIoT-related products and strategies.
Randy Steele
Maintenance Manager; California Oils Corp.
Matthew J. Woo, PE, RCDD, LEED AP BD+C
Associate, Electrical Engineering; Wood Harbinger
Randy Oliver
Control Systems Engineer; Robert Bosch Corp.
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
Design of Safe and Reliable Hydraulic Systems for Subsea Applications
This eGuide explains how the operation of hydraulic systems for subsea applications requires the user to consider additional aspects because of the unique conditions that apply to the setting
click me