Unit 3 - Simple Machine - Class 9

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 moment.

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 another point of machine.

34.  Define pulley.

-          Pulley is a wheel made up of wood or metal that rotates on an axle.

35.  Classify the pulley.

-          Pulley can be classified into three types:

i.                    Fixed pulley

ii.                  Movable pulley and

iii.                Block and Tackle pulley

36.  Define fixed pulley, movable pulley and block & tackle pulley.

-          Fixed pulley: The pulley which does not move with the load is called fixed pulley. It is used in well to pull water.

-          Movable pulley: The pulley which moves up and down with the load is called movable pulley.

-          Block & Tackle pulley: Block & Tackle pulley is the combination of fixed and movable pulley.

37.  How velocity ratio of pulley can be calculated?

-          Velocity ratio of pulley can be calculated as:

i.                    For fixed pulley: VR = 1

ii.                  For movable pulley: VR = 2

iii.                For block & tackle pulley: VR = No. of pulleys used.

38.  Fixed pulley can’t magnify effort, but it is used for simple machine, why?

-          It is because:

i.                    Fixed pulley changes direction or force.

ii.                  It transfers force from one point to another point.

iii.                It increases the rate of doing work

39.  A pulley system has 80% of efficiency. What should be the number of pulley if MA to be 4? What should effort to be applied to overcome the load of 1000N?

-          Given,

Efficiency (ŋ) = 80%

MA = 4

Load = 1000N

No. of pulley (VR) = ?

Effort = ?

We know that, Efficiency (ŋ) = (MA/VR) x 100%

            or, 80% = (4/VR)x100%

            or, VR = 4x100/80

            or VR = 5

Therefore, no. of pulley should be 5.

Again, MA = Load/Effort

            or, 4 = 1000/Effort

            or, Effort = 1000/4
            or, Effort = 250N

        

40.  Define wheel and axle with suitable example.

-          Wheel and axle consist two cylinders having different diameter fitted in one common axis. Larger is called wheel and smaller is called axle. For example, steering, pedal of cycle etc.

-          In another language wheel & axle can be defined as a device having two co-axial cylinders

41.  How velocity ratio of wheel and axle can be calculated?

-          Velocity Ratio of wheel and axle (VR) = Radius of wheel (R)/Radius of axle(r)

42.  Wheel and axle is known as continuous lever, why?

-          It is because it can rotate continuously up to 360⁰ to perform work but ordinary lever can rotate only up to 90⁰. So, it is called as continuous lever.

43.  Define Inclined plane.(Inclined plane can be defined in so many ways, you may choose any one)

-          Inclined planes are slanted surfaces which are used for movement up to some height.

-          A plane that makes an angle with a horizontal plane is called an inclined plane.

-          A slope that reduces the effort to lift a load is called inclined plane.

-          For example, roads on hill and mountains, ladder, plank etc.

44.  How velocity ratio of inclined plane is calculated?

-          Velocity ratio of inclined plane is calculated as

(VR) = Length of inclined plane (l)/Height of inclined plane (h)

45.  What should be done to load the same mass on a truck?

-          The length of inclined plane should be increased because less effort is required for longer plane and more effort is required for shorter plane.

46.  What is moment?

-          The turning effect of force (torque) about a point is known as moment.

47.  How moment can be calculated?

-          Moment can be calculated as, Moment = Force X Perpendicular distance from fulcrum

48.  In which factors moment depends?

-          Moment depends on force and length of arm.

49.  The probability of breaking of taller tree is more why?

-          It is because taller tree has more perpendicular length from its root (fulcrum), so turning effect (moment) is more. So, probability of breaking or taller tree is more.

50.  Define law of moment.

-          When a body is in equilibrium, the sum of the clockwise moment about a point is equal to the sum of the anticlockwise moment. It is called the law of moment.

-          GOOD LUCK -

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