1.
What
do you mean by simple machine?
-
The
devices which are very simple in structure and make our daily work easy, faster
and convenient are known as simple machines. For example: knife, pen, forceps,
scissors etc.
2.
How
do the simple machines make our works easier?
-
The
simple machines make our works easier in the following ways:
i.
They
increase the speed of doing work
ii.
They
transfer the force from one point to another point.
iii.
They
multiply the applied force.
iv.
They
change the direction of applied force.
3.
Name
the type of simple machines.
-
The
simple machines are of six types on the basis of their structure which are:
Lever, Pulley, Wheel & Axle, Screw, Wedge, Inclined plane.
4.
What
is effort?
-
The
external force applied to a simple machine to make it work is known as effort.
5.
What
is load?
-
The
resistance which is overcome by a machine is known as load.
6.
What
do you mean by input work?
-
The
energy applied to a machine to make it work is known as input work. In another
word, input work can also be defined as the work done on the machine by effort
is known as input work. Mathematically, Input Work = Effort X Effort Distance
7.
What
do you mean by output work?
-
The
performance of machine while overcoming load is known as output work. In
another word, the work done by the machine is known as output work.
Mathematically, Output work =
Load X Load Distance
8.
What
do you mean by Mechanical Advantage?
-
Literally,
Mechanical Advantage is defined as the capacity of a machine to magnify the
effort. Mathematically, it can be defined as the ratio of Load to Effort i.e.
MA = Load/Effort. (It doesn’t have any
unit, because it is a ratio.)
9.
What
do you mean by Velocity Ratio?
-
The
Velocity Ratio is defined as the ratio of Effort Distance to the Load Distance.
Mathematically, VR = Effort Distance/Load Distance. (It doesn’t have any unit,
because it is a ratio.)
10. Why
VR is always greater than MA?
-
It
is because the MA is depends on friction while VR depends on the structure of a
machine. So, VR is always greater than MA.
11. A
machine has MA = 4, what does it mean?
-
It
means that the machine can magnify effort by 4 times.
12. A
machine has VR = 5, what does it mean?
-
It
means that the machine has Effort distance 5 times greater than Load distance.
13. Define Efficiency?
-
Efficiency
is defined as the ratio of Output work to the Input work expressed in
percentage. Mathematically, Efficiency(ŋ) = (output work/Input work)X100%
-
Similarly,
it can also be defined as the ratio of Mechanical Advantage to the Velocity
Ratio expressed in Percentage. Mathematically, Efficiency(ŋ) = (MA/VR)X100%
14. No
any simple machine has 100% of efficiency, why?
-
It
is because some of the input energy is lost due to the friction. So, no any
simple machine has 100% of efficiency.
15. A
machine has 78% of efficiency, what does it mean?
-
It
means that 22% of input energy is lost due to friction, only 78% of input work
converted into output work.
16. What do you mean by ideal or
perfect machine?
-
The
imaginary machines which have 100% of efficiency and do not contain any
friction are known as idea or perfect machines.
17. Differentiate
between simple machine and ideal machine.
-
The
following are the differences between simple machine and ideal machine:
Simple
Machine
|
Ideal
Machine
|
1.
These
bear friction.
|
1. Theses do not
bear any friction.
|
2.
These
never have 100% of efficiency.
|
2. These always have 100% of efficiency.
|
3. These are real machines.
|
3.
These are imaginary machines.
|
4. These are of six types.
|
4.
These do not exist in real life.
|
18. What is the working principle of
a simple machine?
-
In
an ideal machine, input work = output work i.e.
Effort X Effort Distance = Load X Load Distance
19. What is the working principle of
a lever?
-
When
a lever is in an equilibrium condition under the action of effort and load,
then input work is always equal to output work i.e. Effort X Effort Distance =
Load X Load Distance.
20. What do you mean by lever?
-
Lever
is the rigid bar which is capable to rotate about a fixed point (fulcrum) to
lift the load is known as lever.
21. What is fulcrum?
-
The
fixed point at which lever is mounted is known as fulcrum.
22. What is effort distance and load
distance?
-
The
distance between fulcrum and effort is known as effort distance or effort arm
and the distance between load and fulcrum is known as load distance or load
arm.
23. What are the types of lever?
-
On
the basis of position of fulcrum, load and effort the lever can be classified
into three classes: (i) First Class Lever (ii) Second Class Lever and (iii)
Third Class Lever
24. Define first class lever with
suitable examples.
-
The
lever in which fulcrum lies between load & effort is known as first class
lever. For example: scissors, Nail Puller, Sea Saw etc.
25. Points
to be remembered for first class lever:
-
We
can adjust Effort Distance and Load Distance in the first class lever.
-
If
ED = LD, then VR = 1, MA=1
-
If
ED>LD, then VR.>1, MA>1
-
If
ED<LD, then VR<1, MA<1
26. In
metal cutting scissors, cutting edges are made shorter than cloth cutting
scissors, why?
-
In
metal cutting process more effort is required than cloth cutting. If cutting
edges are made shorter, MA will be greater than 1 i.e. effort will be
magnified. So in metal cutting scissors, cutting
edges are made shorter.
27. Define second class lever.
-
The
lever in which load lies between fulcrum and effort. For example: Nut cracker,
bottle opener etc. (in second class
lever ED>LD, so VR & MA are always greater than 1)
28. Define third class lever.
-
The
lever in which effort lies between fulcrum and load is known as third class
lever. For example: forceps, stapler etc. (in
third class lever ED<LD, so VR & MA are always less than 1).
29. A lever of length 1m has been
used to lift a load of 600N by applying an effort of 200N. If load is at 20cm
from fulcrum, calculate mechanical advantage, velocity ratio and efficiency.
-
Given, Effort = 200N
Load = 600N
Load Distance = 20cm
= 20/100 = 0.2m
Effort Distance =
1-0.2 = 0.8m
MA = ?
VR = ?
Efficiency = ?
We know that, MA = Load/Effort
= 600/200
= 3
VR
= ED/LD
= 0.8/0.2
= 4
Efficiency
= (MA/VR)X100%
= (3/4)X100%
=300/4
= 75%
30. A load of 400N is lifted by an
effort of 100N. If load distance is
20cm, what will be the effort distance?
-
Given Load = 400N
Effort = 100N
Load Distance = 20cm =
20/100 = 0.2m
Effort Distance = ?
We know that, Effort X Effort Distance = Load X
Load Distance
or, 100 X Effort
Distance = 400 X 0.2
or, 100 X Effort
Distance = 80
or, Effort Distance =
80/100
or, Effort Distance =
0.8m
31. A
long spanner is used to open a knot, why?
-
It
is because a long spanner has greater mechanical advantage than smaller one due
to its long effort distance. So a long spanner is used to open a knot.
32. Differentiate
between MA & VR.
-
Following
are the differences between MA & VR:
MA
|
VR
|
1.
It
is the ratio of load to effort
|
1. It is the
ratio of Effort Distance to Load Distance.
|
2. It depends on the friction.
|
2.
It depends on the structure of a machine.
|
33. Forceps
are used in daily life even it has MA is less than 1, why?
-
Because
it increases the speed of our daily works and transfers from one point to the
another point of machine.
Have a Good Luck and Thanks for Reading.
Please Post your comments, likes or sharing.
ReplyDelete