Chap 3 design of machine elements subjected to bending

CHAPTER 3DESIGN OF MACHINE ELEMENTS

SUBJECTED TO BENDING

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Aim:

To understand how the three types of levers work and appreciate the

advantages/disadvantages of each one.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Expected Knowledge• Force

• VelocityKey Vocabulary

• Lever• Fulcrum

• Resistance• Effort

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Levers are…

• Simple machines that help us apply force.

• Rigid structures, hinged at some part with forces applied at two other points.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

We have levers within our body, and also use them externally for many different

reasons.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

All levers have three parts:

• Fulcrum • Resistance

• Effort

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Fulcrum

The pivot point.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Resistance (or load)

The weight that needs to be moved.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Effort

The force that is applied to move the resistance (or load).

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Levers perform two main functions:

To increase the resistance

(or force) that can be moved with a given effort e.g. a crowbar.

To increase the velocity at

which an object will move with a

given force. E.g. A golf club.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

FUNCTIONS of Levers

There are 3 classes of levers.

Each is structured in a different manner and has different

advantages.

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CLASSES of Levers

The fulcrum lies between the effort and the resistance.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

First class Lever

First Class Levers

Using a crowbar to move a rock.

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Principle of Levers

First Class Levers

Using a hammer to pull out a nail.

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Principle of Levers

First Class Levers

A see-saw.

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Principle of Levers

First Class Levers

Up and down movement of the head about the atlas joint.

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Principle of Levers

First Class Levers

Pulling an oar in a row boat.

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Principle of Levers

Second Class Levers

The resistance lies between the fulcrum and the point of effort.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Second Class Levers

The movement of the foot when walking.

(the calf muscle provides the effort and the ball of the foot is the pivot)

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Second Class Levers

Opening a door by the handle.

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Principle of Levers

Second Class Levers

Opening a bottle with a bottle opener.

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Principle of Levers

Second Class Levers

Pushing a wheel barrow.

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Principle of Levers

Third Class Levers

The effort lies between the resistance and the fulcrum.

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Principle of Levers

Third Class Levers

Biceps curl.

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Principle of Levers

Third Class Levers

Fishing with a rod.

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Principle of Levers

Third Class Levers

SUDHIR PATEL L.J.

POLYTECHNIC,A'BAD

Swinging a bat to hit a ball.

Principle of Levers

Application

Long levers

provide amplified power at the expense of speed of movement of the object being

moved.

Examples: – Using a jack to lift a crashed car.– Using a knife to get the lid off a tin.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Application

Short leversprovide speed

at the expense of power

Example: Levers designed to accelerate objects include:- Most body limbs used for throwing or

kicking because the muscle inserts near the pivot point.

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers

Application

• Can you think of sporting examples where there are longer and shorter levers?

• What happens to the effectiveness of a lever if the fulcrum is moved closer or further away from the load?

MISSAM RAZA Dept. -Mechanical LJ Polytechnic

Principle of Levers