12 – SIMPLE MACHINES
Q. 1. Classify the following as a lever, a pulley and an
inclined plane :
A wedge, a needle, a staircase, a slide, the wheel of a
flagpole, nutcrackers, scissors an opener, an axe, a crane, a knife.
Ans.
• Simple machines : A lever, a pulley, a inclined plane, a
wedge.
• An inclined plane : A slide and a staircase.
• Wheel and axle :
The wheel of a flagpole.
• Wedge : A needle, an axe and a knife.
• Lever : nutcrackers, scissors, an opener.
• Complex machine : A crane.
Q. 2. Fill in the blanks using the proper word and complete
the statements :
(1) The ................ in the
centre, the ................ on one side and the .............. on the other
side make a lever of the first order.
(2) The ............. in the centre, the……....... on one
side and the ............. on the other side make a lever of the second order.
(3) The
................. in the centre, the ................ on one side and the
................. on the other side make a lever of the third order.
Ans. (1) The fulcrum in the centre, the load on one side and
the effort on the other side
make a lever of the first order.
(2) The load in the centre, the fulcrum on one side and the
effort on the other side make a lever of the second order.
(3) The effort in the centre, the load on one side and the
fulcrum on the other side
make a lever of the third order.
Q 3 Which
machines will you use to do the following work? Write their types.
The answers are given directly.
(1) To remove the lid of a tin (2) To lift bricks to the top
of a tall building (3) To cut
vegetables, (4) To draw water from a well.
(5) To hold a papad for roasting it.
Ans.
|
Work |
Machine |
Type
of a machine |
|
(1) To remove the lid of a tin |
Can opener |
Inclined plane (Screw) |
|
(2) To lift bricks to the top of a tall building |
A wheel and a rope to pick up
the heavy load |
Pulley |
|
(3) To cut
vegetables |
Knife or cutter |
Wedge |
|
(4) To draw water from a well |
Water wheel or rope |
Pulley |
|
(5) To hold a papad for roasting it |
A pairs of tongs |
Lever |
Q. 4. Write the
answers to the following questions in your own words:
(1) What is meant by simple machines?
Ans. Devices which are used for
day-to-day work to perform the work efficiently, in less time and with less
effort are called machines. The machines that have only one or two parts and
have simple and easy structure are called simple machines.
(2)
Mention the advantages of using a machine.
Ans. If machine is used, we can
finish the work in less time and with less effort. If machines are not used, we require more time
and more effort to complete even the simple tasks.
(3) What is meant by
complex machines ?
Ans. The machines in which many parts are joined with each
other are called complex machines. Different processes take place in these
individual parts. The structure of such machines is complicated. When a complex
machine is made, it may connect two or more simple machines in it.
(4) What is a
lever ? How are the orders of the lever determined?
Ans.(A) Lever is a simple machine having three components.
viz. fulcrum, load and effort.
(1) The support at which the rod of a lever rests is called
a fulcrum.
(2) The rotation of a lever takes place around a fulcrum.
(3) The weight lifted
by a lever is called a load. The load arm is the arm from the fulcrum to the
load.
(4) The force effort and the applied on the other side of
the lever is called effort. The arm between the effort the fulcrum is called
effort arm.
(B) the type of lever depend upon the positions of load,
fulcrum and effort .
In the first type of lever, the fulcrum is in the centre in
the second type of lever load is in the centre and in the third type of lever,
effort is in the centre. The other two components are on the either side.
(5) What is an Archimedes screw ? Where was it used for the first time?
Ans The well-known scientist Archimedes invented a machine
which is called Archimedes screw. It consists of a round pipe which is fitted
with a rod inside it. This pipe was placed at
an angle of 45. Its one end is inside the water and the
other end having rod rests on a flat surface. By turning the rod, water gets
lifted up in this device.
This machine was used to lift the
water from the hold of a ship.
How are machines
maintained?
Ans The maintenance of the machines is done in the following
ways (1) All the parts of a machine are wiped clean (2) Oil and other
lubricants are applied between the parts that may have friction. This reduces
wear and tear of the machines. (3) Machines are kept covered so that the dust
does not settle on them. (4) Metallic parts of the machine are painted externally
so that they don't catch rust. (5) Machines are always kept dry.
Q 5. Why is this so?
(1) Traveller's bags have wheels.
Wheel is a simple machine. If the heavy bag is to be lifted,
it will require more effort. Instead, drawing it on wheels become easier and
efficient. It consumes lesser time and lesser energy to carry a bag. Therefore,
traveller's bags have wheels
(2) Machines
have to be maintained.
Ans. Parts of the machine undergo wear and tear. Due to
constant rubbing some parts may even get damaged. The weather, the rust and the
dust may spoil the parts of the machines. If the machine is not functioning
well, we may not use this facility when we need it the most. Therefore,
machines need to be maintained regularly.
(3) A bicycle
is said to be a complex machine.
Ans. A bicycle is made from combination of two to three
simple machines. The pedals, the handle. the wheels and the axle all are simple
machines. In combination they work together, therefore a bicycle is said to be
a complex machine.
Q 6 Name the levers mentioned in the following passage.
Identify the fulcrum, load and effort of each and say which type of lever it is
:
trees in the garden
Ravi gets thirsty
Ravi and Savita sit on a see-saw in a garden. In the
meantime, a gardener is trimming trees in the garden. He puts the leaves and
other garbage in a wheelbarrow. Later. Ravi gets thirsty and he buys lemon
sherbet. The sherbet seller cuts the lemon and squeezes it
using a lemon squeezer. He puts small pieces of ice in the
glass with help of the tongs.
Ans In the above paragraph there are simple machines : Their
fulcrum, load and effort are as follows. The type of lever used is dependent on
these positions.
|
Simple
machine |
Fulcrum |
Effort |
Load |
Type |
|
See-saw |
Centre |
On one side |
On the other side |
First |
|
Scissors |
Centre |
On one side |
On the other side |
First |
|
Wheelbarrow |
On one side |
On the other side |
Centre |
Second |
|
Lemon squeezer |
On one side |
On the other side |
Centre |
Second |
|
Tongs |
On the other side |
Centre |
On one side |
Third |
