MACHINES

MACHINES
It is a device that simplifies work.

How do machines simplify work
1. By changing the direction of force.
2. By reducing the effort required to do work
3. By increasing the speed of work.
Types of machines
1. Simple machines.
2. Complex machines.

A complex machine
It is a machine that is made up of many parts and simplifies work.
When two or more simple machines (tools) are put together a complex machine is made
Examples of complex machines
Tractor, Bicycle, Sewing machine, Car, Aero plane etc.

Simple Machine.

It is a device that is made up of few parts and simplifies work.
Examples of simple machines.

A hoeSee sawClaw hammerNut cracker.Human arm.Nut cracker.
A wheel barrowPincers.Water pumpSugar tongs.Spade.Sugar tongs.
A pair of scissorsCrow bar.Bottle openerFishing rodLadder.Stairs.


Classes of simple machines.
1. Levers
2. Inclined planes/slope
3. Pulleys.
4. Screws.
5. Wheel and axle
6. Wedges
Levers
Is a stiff rod that turns on a fixed point called a pivot or fulcrum.

Parts of a lever


1. Effort: is the force exerted on a machine to overcome the load.
2. Load / resistance: it is the weight of the body to be lifted.
3. Fulcrum or Pivot: is the turning point of a machine.
4. Load arm is the distance between the fulcrum and the load.
5. Effort arm is the distance between the fulcrum and the effort.


Classes of levers.
There are three classes of levers depending on the position of the fulcrum(f), Load(l) and effort(E)
First class levers
Fulcrum/pivot is between the load and effort

In this class, the effort arm is longer than the load arm.
The longer the effort arm, the smaller the effort applied.
The advantage of the first class lever is that less effort is used.
Examples of first class levers.

1 57
3
  

Second class lever
Load is between the fulcrum and effort.
The fulcrum and the effort are on either side. (FLE OR ELF)

The load is closer to the fulcrum than the effort
The effort applied is smaller compared to the load.
First and second class levers are referred to as force multipliers

Examples of second class levers.

11

Third class levers


Effort is between fulcrum and load
The fulcrum and the load are on the either side. (FEL)

The effort is closer to the pivot than the load
The effort used is greater than the load.
Third class levers are referred to distance multipliers.

The advantage of using this class is that the effort moves through a shorter distance
Examples of third class levers

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N.B
The formula PLE or FLE can help to determine the class of lever

The principle of moments. (The law of the lever)
The load force multiplied by the load arm is equal to the effort force multiplied by the effort arm.// it states that clock wise moments are always equal to anti-clock wise moments

Examples

  1. A man weighs 60 kgf. He sits 1.5 metres from the fulcrum of the see saw. How far from the fulcrum will the boy whose weight is 30 kgf sit in order to balance the man.
    Let the man be the effort and the boy be the load.
    Let the load be x metres.

3. A weight of 120 grams at a distance 3cm from the fulcrum is balanced by a weight of 30g on the other side. Find the distance from the 30kg weight to the fulcrum.
Take 120kgf as the effort and 30kg as the load.
Let y be the distance of the load from the fulcrum.
Then Load x load arm=Effort x Effort arm.
               30 x y             =120gf x 3cm
                  30y              = 360
                  30                     30
                      y              =12cm

The inclined plane (slope)
An inclined plane is a slanting surface.

Importance of an inclined plane.

  • It enables heavy loads to be raised using a lesser effort.
    Examples of inclined plane

Mechanical Advantage of machines.

Mechanical Advantage is the ratio of the load to effort. i.e. M.A = Load/effort.
M.A is the number of times a machine simplifies work.
M.A has no units since it is a ratio.
Friction lowers M.A.
Example;
John used a slope to raise a load of 60kgf from the ground to the higher level as shown below.

1

Work out the following

The effort distance=5m

The load distance=4m

Work done W=FXDM. A= Load Effort= Distance effort moves

Distance load moves=54

Work

Work is a product of force and the distance moved.

Work=Force x Distance moved.

Work done by the effort=effort x effort arm.

Work done by the load= load x load arm.

The unit of work is a joule.

The unit of force is the Newton.

The standard unit of distance is the metre.1 kgf = 10N1 joule(of work) is done when one newton (of force) moves through one metre( of distance)1 joule=1 N x 1 m1 joule=1 Nm

WEDGES

A wedge is a cutting tool. It is double inclined plane/slope.Examples of wedges

2
3

SCREWS

DIAGRAM SHOWING A SCREW.

screw

A screw is an inclined plane wound round

We use it to make our work easier.USES OF SCREWS

  1. Lifting very heavy things e.g. screw jack.
  2. It makes movement upstairs easier e.g. using a spiral staircase
  3. Used to fasten things together.

EXAMPLES OF SCREWS

types of screw

Wheel and axle

An axle is a rod passed through a wheel.The wheel rotates on an axle

.Examples of devices that use wheels and axles.

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USES OF WHEEL AND AXLE

  1. Drawing water from underground tanks using windlass/winch.
  2. Drilling holes in wooden materials using the brace
  3. Turning screws to fix things together using a screw jack.
  4. It helps in loosening the screws.
  5. Preparing eggs for frying using egg beaters