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Machines Feedback

by Ron Kurtus

Readers have sent in a total of 42 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

What is efficiency? Efficiency USA
 
Contact surface in rollers Rollers Pakistan
 
Direction of motion Three Lever Classes Tanzania
 
Not part of bicycle Three Lever Classes Guyana
 
Real world example Simple Machines USA
 
Force from pliers Three Lever Classes India
 
Property in lever classes Three Lever Classes Tanzania
 
Output work Efficiency Nepal
 
Output distance fir workbench Increasing Distance Moved with a Lever USA
 
Which is better pulley to use? Three Lever Classes USA
 
What type of lever is it? Levers India
 
What is the object lifted by a lever? Levers India
 
I need the proof of efficiency of machine General Nigeria
 
Class of lever of pressure cooker Three Lever Classes USA
 
When is change significant Mechanical Advantage USA
 

Next 15 letters

 





Efficiency

What is efficiency?

July 12, 2019

Question

What is efficiency?

Aeesha - USA (29104)

Answer

The efficiency of a machine indicates how well its input energy is converted to useful output energy or work. In other words, efficiency is the output work divided by the input work.

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Rollers

Contact surface in rollers

May 20, 2019

Question

As the friction does not depend upon the surface of contact then how rolling reduces the friction?

Abdur - Pakistan (29046)

Answer

If you consider sliding an object across the ground, you can see that using rollers or wheels results in much less friction.

The only friction in using rollers is due to a slight "stickiness" an the contact surface. But this is negligible.

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Three Lever Classes

Direction of motion

May 9, 2019

Question

With reference to the explanation given on the second class lever, you said the movement of both load and effort are in the same direction. THIS IS NOT CORRECT. Take an example of a wheelbarrow which in the second class, in it the load (weight) is directed downward while an effort which is applied is directed (acting) upwards, therefore the movements of these forces (load and effort) are opposite.
Thanks,
I'll be glad to get your reaction.

Issa - Tanzania (29029)

Answer

Thank you for your observations. With a wheelbarrow, you pull upward on the handles to raise the load.

I updated the images on Three Lever Classes to clarify the directions on the motions for the various lever classes.

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Three Lever Classes

Not part of bicycle

April 7, 2019

Question

which simple machine is not a part of the bicycle: pulley, lever, screw, or wedge?

fiaz - Guyana (28992)

Answer

You push on the pedals, which is a lever. The bicycle chain forms a pulley. Bicycles have screws to to hold things together. However, I can't think of where a wedge would be used, so a wedge probably is not part of a bicycle.

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Simple Machines

Real world example

January 28, 2019

Question

on youtube there is a 94 year old man using a tool called OTLVISE and He moves 300 lbs up stairs by Himself with it... Using a real world example teaches better the use of a simple machine as it uses a lever, wheels and a clamp with offset ergonomic handles.

john - USA (28925)

Answer

That sounds like an interesting device. Apparently, it is also used to move pool tables.

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Three Lever Classes

Force from pliers

December 11, 2018

Question

When an effort of 50N is applied on a pair of Pliers, it can overcome a load of 250 N. It is given the distance between fulcrum and load is 6cm. Find the length of the Pliers.

Chinmay - India (28875)

Answer

Increasing Force with a Lever gives the equation FO/FI = dI/dO.

In your problem, FI = 50 N, FO = 250 N, and dO = 6 cm. Thus dI = (6 * 250)/50 = 30 cm.

The total length of the pliers is 30 + 6 = 36 cm.

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Three Lever Classes

Property in lever classes

October 7, 2018

Question

What is the peculiar property does the effort has in all class levers

Hamis - Tanzania (28740)

Answer

It is the distance from the fulcrum.

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Efficiency

Output work

June 19, 2018

Question

In a machine a load of 3000N is lifted by 500N effort if the load travels a distance of 2m & effort travels a distance of 16m calculate
Ma, VR input work output work & efficiency

Krishtina - Nepal (28591)

Answer

There are three types of mechanical advantage: Distance, Force, and Speed. See Mechanical Advantage.

Force MA would be 3000/500 = 6.

Work is force x distance moved. Input work = 3000N x 2m.

If there are no losses due to friction, Efficiency = output work/input work.

I hope that helps.

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Increasing Distance Moved with a Lever

Output distance fir workbench

May 27, 2018

Question

Sir:
As a preamble, I'm in the process of building a wood shop workbench with hidden tools. (router, table saw, planner) i.e. when I press a button my tools rise up out of the bench. I've experimented with scissor lifts and winches, but now I'm liking your idea of using a Class 3 lever powered by a linear actuator.

Increasing Distance with a Lever

Now to my question: if DO/DI = do/di, I get DO = (do/di)xDI. Plugging in some numbers using do =67, di =20 and DI =52, I get DO = 174.2. My confusion is, in a class 3 lever, how can DO be significantly greater than do?

Thank you,
John M Hine, MD

John - USA (28566)

Answer

You are really looking at having a mechanical advantage, where the output distance (DO) is much greater than the distance of the output to the fulcrum (do). See Distance Mechanical Advantage for more information.

Off hand, I would think a screw configuration might work better than an lever.

Best wishes for success in makig your workbench. Let me know how things turn out.

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Three Lever Classes

Which is better pulley to use?

April 20, 2018

Question

Dear Ron,

I was reading a lot about the 3 classes levers, and must say that the explanation in your website was the most clear and easy to understand - thank you for this! (the example also really helped).

I have question regard the efficiency of a machine which utilize class 1 lever vs. machine which utilize class 3 lever. which one is better?

For example:
Case 1 (class 1 lever):
I have a long board, where a fulcrum is located in the middle in away that it divides the board into 2 parts of even length on both sides (in other words: a seesaw). Effort arm length = load arm length.
There is a load = X, and Effort= Y.
In such case, I push with effort X on one side, and the load Y will go up on the other side.

Case 2 (class 3 lever):
I have long board based on a fulcrum with a bearing on one side, and I pull the load up (maybe with a small cable in the end)
There is a load = X, and Effort= Y.
Effort arm length = load arm length.

In which case it will be easier to lift the load X up, assuming I would like to reach the same height in both cases?

Thank you!

Al - USA (28532)

Answer

I'm glad the material was useful to you.

Machine efficiency concerns losses due to friction, heat, etc. In the case of a lever, there is very little friction, so its efficiency should be 100%.

Usually, it is easier to push down on a lever, because you can use gravity to help you. However, pulling up on the load with a cable or even using a pulley could work better for you.

I hope that helps.

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Levers

What type of lever is it?

March 20, 2018

Question

I scoop hockey ball which lever applied
I hit six in cricket which lever apply

Dinesh - India (28478)

Answer

Look at where the effort force is applied, where the pivot point is, and where the load or output is to determine the type of lever. See Three Lever Classes for more information.

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Levers

What is the object lifted by a lever?

March 5, 2018

Question

The object to be lifted by a lever is called...???

Pradip - India (28467)

Answer

The object lifted by a lever is usually called the load.

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General

I need the proof of efficiency of machine

February 24, 2018

Question

I need the proof of efficiency of machine

Chibueze - Nigeria (28454)

Answer

The efficiency of a machine depends much on reducing losses due to friction.

See Efficiency of Machines for more information.

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Three Lever Classes

Class of lever of pressure cooker

January 5, 2018

Question

Pressure cooker is which type of class lever? Can we say pressure cooker simple machine?

Bhima - USA (28376)

Answer

Since a pressure cooker has no moving parts,, it could be considered a form of simple machine, where heat creates an internal pressure.

However, it is not a lever and really has no moving parts. But the heat can create pressure and a force.

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Mechanical Advantage

When is change significant

September 19, 2017

Question

Is there a point at which a change in mechanical advantage is considered to be empirically significant? +/-5%? +/-7%?

Greg - USA (28245)

Answer

The actual mechanical advantage of a given configuration can have a tolerance variation according to how accurate it is measured. This would have to be taken into consideration when seeing how significant a change would be. I really don't have any numbers, because it depends so much on the configuration.

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