# Machines Feedback

by Ron Kurtus

Readers have sent in a total of 37 comments and questions on Machines issues. They are listed according to date.

## List of most recent 15 letters

### Country

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

Materials for levers Levers India

Efficiency of a screw jack Efficiency Ghana

Increasing efficiency through use Efficiency Nigeria

Finding center of gravity of a small machine General Australia

Next 15 letters

## 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)

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.

## Property in lever classes

October 7, 2018

### Question

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

Hamis - Tanzania (28740)

It is the distance from the fulcrum.

## 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)

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.

## 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)

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.

## 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)

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.

## 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)

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.

## What is the object lifted by a lever?

March 5, 2018

### Question

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

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

## I need the proof of efficiency of machine

February 24, 2018

### Question

I need the proof of efficiency of machine

Chibueze - Nigeria (28454)

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

## 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)

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.

## 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)

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.

## Materials for levers

March 8, 2017

### Question

With what material mechanical lvers are made up of?
And what are the operation of mechanical levers?

Thank you :)

Chinmoy - India (27933)

A lever can be made of any material that is solid and strong enough to withstand a force. This includes some board used to lift an object on a pair of pliers. Look at the examples on the lever pages.

## 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)

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.

## Increase mechanical advantage in simple machine

January 4, 2017

### Question

How can mechanical advantage of simple machines be increased

mercy sharleen - Uganda (27782)

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

## Increasing efficiency through use

December 26, 2016

### Question

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

Felix - Nigeria (27581)

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.

## 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)

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.

## Misc

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.

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