What is a machine?

Large and complex devices?Scissors, pliers and spanners are called
simple machine.

A simple machine which consists a bar
that turns about a fixed point called
fulcrum.Example: scissors, spanners, bottle
openers, pliers, staplers, nut crackers,
paper cutters and wheelbarrows.

scissors

Bottle openers

Pliers

staplers

Nut cracker

Wheelbarrows

A lever enables a small effort to
overcome a large load.The long stick is called the lever.

Effort (E)

Load (L)

Fulcrum (F)

Effort (E)

Load (L)

Fulcrum (F)

E = which is the force exerted by the boy.

F = which is the fixed point where the lever turns about.

L = which is the force from the large rock which must be overcome.

P

Q

The longer the distance of the effort from the fulcrum, the less effort is required to lift the load.If the man presses downwards at point Q, he will need to use more effort to lift the load.

Levers can be classified into three classes:

First class leverSecond class leverThird class lever.

depend on the position of the fulcrum.

fulcrum

effort

load

First class lever

The fulcrum is between the load and the effort.The load and the effort act in the same direction.

Advantages

A small effort can lift a heavy load if the effort arm is longer than the load arm.

fulcrum

load

effort

effort

load

hammer

A pair of pliers

-TIN OPENER

-SCISSORS

fulcrum

effort

load

Second class lever

The load is between the fulcrum and the effort.The load and the effort act in the opposite direction.

Advantages

The effort is always less than the load.

Wheelbarrows

Nut cracker

L

F

E

L

F

L

E

E

-PAPER CUTTER

-BOTTLE OPENER

fulcrum

effort

load

Third class lever

The effort is between the fulcrum and the effort.The load and the effort act in the opposite direction.

Advantages

A short distance moved by the effort makes the load move through a longer distance.

staplers

L

E

F

Fishing rod

L

E

F

-ICE TONG

-FORE-ARM

fulcrum

effort

load

fulcrum

load

fulcrum

load

The Principle of a first class lever.

load

effort

fulcrum

Load arm

Effortarm

Load X load arm = effort X effort arm

The Principle of a second class lever.

load

effort

fulcrum

Load arm

Effortarm

Load X load arm = effort X effort arm

The Principle of a third class lever.

load

effort

fulcrum

effort arm

Load arm

Load X load arm = effort X effort arm

Attention !!!!

The load arm is the distance from the load to the fulcrum.

The effort arm is the distance from the effort to the fulcrum.

Worked example 1

2N

30cm

effort

80cm

What effort is required to keep the lever in a horizontal position?

Effort X effort arm = load X load arm

Effort X (80 30) = 2 X 30

Effort = 2 X 30 = 1.2N

50

Worked example 2

load

4N

1m

Calculate the weight of the load.

Load X load arm = effort X effort arm

Load X (100 60) = 4 X 100

Load = 4 X 100 = 10 N

40

effort

60cm

Worked example 3

9N

Effort = 12 N

80cm

At what distance from the fulcrum must the effort act to maintain the lever in a horizontal position?

Effort X effort arm = load X load arm

12 X E = 9 X 80

E = 9 X 80 = 60cm

12

The moment of force

1.When we open a door or use a spanner to loosen a nut, we are applying a force that causes a turning effect to accomplish the desired task.

2. The turning effect is called the moment of force.

3.The moment of force is the product of the force and the perpendicular distance from the fulcrum to the force.

d

Force

Moment of force (Nm)= force (N) X
perpendicular distance (m)

From the equation:

The greater the force used, the greater is the moment of force.The longer the distance, the greater is the moment of force.

activity :10.2

Aim:To show the relationship between moment and the product of force and distance.

Diagram: Figure 10.6

Procedure:

1.The apparatus was set up as shown in Figure 10.6. The fulcrum was at the 5cm mark of the half-metre rule while the 5N weight was hung from the 15 cm mark.

2.The spring balance was used to lift the other end of the half-metre rule at the 45cm mark. When the half-metre was horizontal, the reading of the spring balance and the distance from the spring balance to the fulcrum were recorded.

3. The product of the force and its distance from the fulcrum was calculate.

4.Steps 2 and 3 were repeated with the spring balance at the 40cm, 35cm and 30cm mark of the half-metre rule.

5.My readings were recorded in the table as shown below.

Observation:

Distance (m)Force (N)Force X distance (Nm)0.40 0.350.300.25

By :