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Machines Feedback

by Ron Kurtus

Readers have sent in a total of 26 comments and questions on Machines issues. They are listed according to date.

You can read them to further your understanding of the subject.



List of most recent 15 letters

Title

Topic

Country

Efficiency of a screw jack Efficiency Ghana
 
Increase mechanical advantage in simple machine Mechanical Advantage Uganda
 
Increasing efficiency through use Efficiency Nigeria
 
Finding center of gravity of a small machine General Australia
 
What do you lose with force advantage? Mechanical Advantage SA
 
What is the physics behind force and a lever? Levers USA
 
Need correction on Class 3 lever Levers USA
 
When is mechanical advantage equal to 1? Mechanical Advantage Nepal
 
Formula for calculating efficiency of a machine Efficiency Nigeria
 
Mechanical advantage greater than 1 Mechanical Advantage Nigeria
 
Why is a class one lever more efficient? Levers Pakistan
 
Using a lever in dental braces Levers USA
 
What type of lever is a bicycle handlebar? Levers India
 
Class of janglover lever Levers Nigeria
 
Rolling friction in bearings Bearings Kuwait
 

Next 15 letters

 





Efficiency

Efficiency of a screw jack

January 5, 2017

Question

A screw jack is being used to support the axle of a tractor,the load on it being 2.4 KN.The screw jack has an effort of effective radius 200 mm and a single-start square thread,having a load of 5 mm.Determine the efficiency of the jack if an effort of 60 N is required to raise the tractor axle.

DAASI - Ghana (27787)

Answer

Efficiency is the output work divided by the input work. Work is defined as the force times the distance moved.

The input force is 60 N and the output force is 2.4 KN. According to your configuration, you need to determine how far the input and output forces move to determine the work ratio.

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Mechanical Advantage

Increase mechanical advantage in simple machine

January 4, 2017

Question

How can mechanical advantage of simple machines be increased

mercy sharleen - Uganda (27782)

Answer

It depends on the type of simple machine. In a lever, you can change the distance from the fulcrum to change the mechanical advantage. See Mechanical Advantage Relationships

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Efficiency

Increasing efficiency through use

December 26, 2016

Question

Can the efficiency of a machine increases through consistent use or frequently ?

Felix - Nigeria (27581)

Answer

Factors that can reduce the efficiency of a machine are friction and heat build-up. In some machines, friction may be increased if it is not used often. This can be due to oxidation of the surfaces. In such a case, using the machine more often can reduce or eliminate this type of friction, thus increasing its mechanical efficiency.

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General

Finding center of gravity of a small machine

October 31, 2016

Question

Hi School of Champions

I've built a small machine in my home workshop that is a little heavy to rotate about an axis, before I redesign it in cad I need to calculate the center of gravity & force required to rotate it based on the current design and compare it to a revised cad design.

I can send a simple image that shows the problem.

Thank you, your help here would be much appreciated.

Darryl - Australia (27428)

Answer

The Center of Gravity article shows ways to find the COG. However, that might not be practical in your situation. But it might give you some ideas.

If you could hang the machine from a wire, you could find the COG. Rotating it from the wire with no friction would depend on its mass.

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Mechanical Advantage

What do you lose with force advantage?

September 28, 2016

Question

When you gain a force advantage you usually lose what?

Sphilile - SA (27334)

Answer

The force mechanical advantage requires a greater input distance than the resulting output distance.

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Levers

What is the physics behind force and a lever?

September 17, 2016

Question

Can you explain the physics behind the lever ? I know how to calculate, and understand it is the product of force*length, but I don't understand the force distribution(?) of why the force is increased due to the length ?
What is the mechanism that makes it works ?

Thank you,
Roy A

Roy - USA (27294)

Answer

That is a very good question, and it is not often mentioned in textbooks.

The relationship between forces and lengths of the lever arms is dependent on the Law of Conservation of Work and Energy. Work is defined as the force times the distance moved.

I updated several pages to show the derivation of the equation. See Increasing Force with a Lever.

I hope that helps your understanding.

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Levers

Need correction on Class 3 lever

July 24, 2016

Question

Please reverse the location of the fulcrum for the 3rd class lever. It should be above the lever, rather than below it. The lever will not work as illustrated. Unlike a 2nd class lever, there's no support there.

Clyde - USA (27167)

Answer

Thanks for pointing that out to me. It was very perceptive of you to notice that. Many resources on Class 3 levers simply place the fulcrum at the bottom.

I updated Levers are Simple Machines and to show requirements for the Class 3 lever fulcrum.

I hope that corrects the issue.

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Mechanical Advantage

When is mechanical advantage equal to 1?

July 18, 2016

Question

in what condition MA<1 MA>1 and MA=1 ?

bhabin - Nepal (27154)

Answer

The mechanical advantage (MA) equals 1 when there is no increase in the output compared to the input. An example is a pulley, where you simply change the direction of the object when you pull on the rope.

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Efficiency

Formula for calculating efficiency of a machine

May 29, 2016

Question

Formular for calculating efficiency of a machine

fatosa - Nigeria (27035)

Answer

The formula for the efficiency of a machine is E = Wo/Wi where Wo is the output work and Wi is the input work.

The output work is always less than the input work, because of losses due to friction and heat.

The work equals force times distance Wo = F*d.

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Mechanical Advantage

Mechanical advantage greater than 1

April 26, 2016

Question

When machanical advantage of a machine is greater than 1,what is the implication ? Is the machine a good machine or a bad machine ?

jimoh - Nigeria (26966)

Answer

You want the machine to have the force mechanical advantage to be greater than 1. That way you can lift a greater load than your effort.

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Levers

Why is a class one lever more efficient?

January 10, 2016

Question

why class one lever is more efficient

sneha - Pakistan (26676)

Answer

Efficiency is related to the distance that the object is moved divided by the distance the force moves. A Class 1 lever is arranged to move the object further for a given force than the other classes of levers.

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Levers

Using a lever in dental braces

December 6, 2015

Question

I am an orthodontist and will be speaking to a high school group soon on applied physics in orthodontics.

My question: attaching a longer wire in front of and behind a displaced tooth (say high up in the gum) certainly places less force on the displaced tooth than if the wire is shorter between the wire attached to the teeth in front and behind:( i.e, the wire is attached to the upper central incisor, bypasses the lateral incisor, attaches to a high displaced canine, bypasses the first bicuspid and attaches to the second bicuspid, thereby bypassing the teeth in front of and behind the high displaced canine to lessen the force to bring down the displaced canine).

What is considered the fulcrum, the load and the force? I presume that the displaced tooth is the load and the adjoining teeth are the fulcrums and the wire is the force? Are both arms of the portions of the wire in front of and behind the tooth considered effort arms vs. load arms?

Also, is this an example of a class one lever or a class 2 or 3 lever? Is there a better way to describe the physics property as to why a longer wire to the displaced tooth exerts lesser force than a shorter wire? Thanks so much for your help! Dr M Wintner, Pittsburgh

Dr. Morton - USA (26592)

Answer

I am not sure I can visualize how the wires are placed and the orientation of the lever. Perhaps the following two articles would help to answer your questions:

Torque control in lingual orthodontics with lever arm mechanics: a case report.

Locating the center of resistance of maxillary anterior teeth retracted by Double J Retractor with palatal miniscrews.

I hope that helps. Best wishes for success in your presentation.

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Levers

What type of lever is a bicycle handlebar?

July 5, 2015

Question

What type of lever is bicycle handle bar

Shantanu - India (26153)

Answer

While a standard lever pivots about a stationary fulcrum, a bicycle handlebar is used to turn or rotate the fulcrum. This is similar to the use of a screwdriver.

Instead of calling it a lever, handlebars could be classified as a tool to create a torque on the steering shaft.

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Levers

Class of janglover lever

June 24, 2015

Question

Which Class Of Lever Is A Janglover?.

Samuel - Nigeria (26120)

Answer

I am sorry, but I don't know what a Janglover is.

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Bearings

Rolling friction in bearings

April 9, 2015

Question

The following is a question appeared in one exam and the two answers
given by two different websites for the same are given below

13. Ball bearings are used in bicycles, cars, etc., because__:
A. The actual area of contact between the wheel and axle is increased
B. The effective area of contact between the wheel and axle is increased
C. The effective area of contact between the wheel and axle is reduced
D. None of the statements is correct

Answer: C
The basic premise in friction theory is that anything that reduced the area of contact between the wheel and axle will decrease the friction. Since the ball is a sphere, it only contacts the wheel and axle at a very small point, which helps it spin very smoothly.

Answer: D
Friction is independent of Surface Area

Hashir - Kuwait (25902)

Answer

If a hard object is sliding on a hard surface, the resistance from friction is approximately independent of the surface area in contact, However, ball bearings aren't meant to slide. Instead, they roll, and rolling friction is different and much less than sliding friction.

The reason ball bearings are used in bicycles and cars is so that they can roll around the axle, as opposed to having the wheel slide around the axle.

See: Rolling Friction for more information.

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