ICSE Living Science Physics for Class 6 Solutions Chapter 7 Simple Machine

Check Your Progress (Page 78)

Answer the following.

Question 1.
What is a machine ?
Answer;
Tools and objects that help us to perform the same amount of work with much less effort than if we did the work manually, are called machines. Example : lever, hammer, knife, etc.

Question 2.
What do you understand by a complex machine ?
Answer:
Machines such as sewing machines or cars that have more than one moving part are called complex machines.

Question 3.
Name the simplest of all types of machines.
Answer:
Lever

Question 4.
State the principle of levers.
Answer:
The principle of a lever states that the product of the load and the load arm is always equal to the product of the effort and the effort arm.
Load x Load arm = Effort x Effort arm
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 1
The above ratio is called the mechanical advantage of a lever.

Question 5.
What is a Class I lever ?
Answer:
In Class I levers (also called levers of first order), the fulcrum lies between the load and the effort, i.e., the load and the effort are on the opposite sides of the fulcrum. Examples : See-saw, pairs of scissors, pliers, beam balance, etc.
The mechanical advantage of a Class I lever is always greater than one. These levers act as force multipliers.
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 2

A. Tick the most appropriate answer.

Question 1.
The force applied on a machine to do work is called the
a. load
b. effort
c. efficiency
d. fulcrum
Answer:
b. effort

Question 2.
If the effort lies between the fulcrum and the load, then the lever belongs to which class ?
a. Class I
b. Class II
c. Class III
d. Class IV
Answer:
c. Class III

Question 3.
Which of the following is a Class II lever ?
a. Pliers
b. A beam balance
c. A nut-cracker
d. A knife
Answer:
c. A nut-cracker

Question 4.
A pair of scissors is an example of a/an
a. wedge
b. lever
c. inclined plane
d. screw
Answer:
b. lever

Question 5.
The mechanical advantage of an inclined plane is always
a. greater than 1
b. less than 1
c. equal to 1
d. zero
Answer:
a. greater than 1

Question 6.
The effort required to lift a load of 800 N by using a lever having a mechanical advantage of 1.6 is
a. 1080 N
b. 240 N
c. 720 N
d. 500 N
Answer:
d. 500 N

Question 7.
A machine made up of two or more sloping surface is known as .a
a. wedge
b. screw
c. pulley
d. lever
Answer:
a. wedge

Question 8.
The useful work done by a machine is known as the
a. input energy
b. output energy
c. efficiency
d. effort
Answer:
b. output energy

B. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
There are four types of simple machines.
Answer:
False. There are six types of simple machines.

Question 2.
The load and effort can act at a single point in a lever.
Answer:
False. The load and effort cannot act at a single point in a lever.

Question 3.
A screw is a special case of an inclined plane.
Answer:
True

Question 4.
The effort required to insert a screw into wood is less than that needed to insert a nail into wood.
Answer:
True

Question 5.
A single movable pulley is a pulley that has its axis of rotation fixed.
Answer:
False. A single fixed pulley is a pulley that has its axis of rotation fixed.

Question 6.
A rotation spindle tap is an example of a wheel-and-axle arrangement.
Answer:
True

Question 7.
A sewing needle is a wedge type simple machine.
Answer:
True

Question 8.
Work done by a machine is always more than the work done on a machine.
Answer:
False. Work done by a machine is always less than the work done on a machine.

C. Answer the following in a word or two or in a sentence.

Question 1.
Given an example of a Class I lever. >
Answer:
See-saw, pair of scissors

Question 2.
Which type of machine is used to squeeze a lemon ?
Answer:
Class II lever

Question 3.
Write the relationship between mechanical advantage, load and effort.
Answer:
Mechanical advantage (MA) = Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 3

Question 4.
Name the type of machine made by putting two inclined planes together.
Answer:
Wedge .

Question 5.
Give one example of a machine used to multiply speed.
Answer:
Class III lever (hockey stick, forceps)

Question 6.
Write the formula for calculating the efficiency of a machine.
Answer:
Efficiency = Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 4
The percentage value of efficiency of a machine is calculated as :
Efficiency = Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 5

D. Answer the following in short.

Question 1.
Explain the various functions that a machine can perform.
Answer:
Various functions that a machine can perform are :

  • Changing the direction of applied force – Example : When a flag is hoisted with the help of a pulley.
  • Changing the magnitude of applied force – Example : Bottle opener multiplies the applied force and much less effort is required to open the cap.
  • Applying force at a convenient point – Example : In a pair . of scissors, the input force is applied at the handle of the scissors which cuts the paper at the other end of the blade.
  • Changing the speed of an object – Example : While riding a bicycle, force is applied on pedals which multiplies the speed.

Question 2.
What is the basis of classification of levers ?
Answer:
Levers are classified on the basis of the relative positions of load, effort and fulcrum.

Question 3.
What is the function of a screw ? Give any one use of a screw.
Answer:
A screw is a special type of an inclined plane which has a sharp and pointed tip and can be turned (using a screw driver, bolt or a jack.) It acts as a force multiplier and less effort is required to do the work. Example : Screw forced and rotated into wood travels a greater distance with less effort than a nail would. Bolt rotating inside the fixed nut and jack used to lift a car use the principle of screw.

Question 4.
Using a suitable example, describe how a machine acts as a force multiplier.
Answer:
It is very difficult to open the sealed metal cap of a cold drink bottle with our bare hands. A simple machine like a bottle opener (Class II lever) multiplies the applied force and much less effort is required to open the cap. Hence, it acts as a force multiplier.

Question 5.
What do you understand by the term ‘efficiency of a machine’?
Answer:
The ratio of the work done by the machine to the work done on the machine is called efficiency of a machine
Efficiency = Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 4
[Work done by a machine is called the output energy and the work done on a machine is called the input energy.]

Question 6.
Mention any two methods by which we can take care of machines.
Answer:
Taking care of machines : Some of the ways in which machines should be cared for are given below.

  1. Machines should be kept in a clean environment, which is free from dust and moisture.
  2. When not in use, machines should be kept covered to prevent collection of dust on them.
  3. Machines made of iron should be protected from rust by coating them with paint.
  4. The moving parts of a machine should be regularly oiled with a good-quality machine oil to reduce friction and wear and tear.

E. Answer the following in detail.

Question 1.
Draw simplified diagrams by clearly showing the position of load, effort and fulcrum for Class I, Class II and Class III levers.
Answer:
Class I –
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 7
Class II lever –
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 8
Class III lever –
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 9

Question 2.
How does a pulley make work simpler ? Differentiate between a single fixed pulley and a single movable pulley.
Answer:
A pulley is a wheel or a circular disc that can rotate freely about its axle. It is used to lift Heavy objects. It is neither a force multiplier nor a speed multiplier. It only changes the direction of the applied force from upwards against gravity to downwards towards gravity. There are two types of pulley systems – Single fixed pulley and single movable pulley.

Single fixed pulley:

  • This pulley has a fixed axis of rotation.
  • The load is attached to one end of the rope.
  • Only the direction of the force is changed, not the magnitude, [We can lift the object higher but heaviness of load remains the same]
  • The mechanical advantage of this pulley is 1.
  • Example : Used to draw water from wells.
    Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 10

Single movable pulley :

  • The axis of rotation of this pulley is not fixed.
  • The load is attached to the pulley.
  • The direction of the force as well as the magnitude of force change.
  • The mechanical advantage of of this pulley is 2.
  • Example : Used in construction cranes, weight lifting, machines in gym, etc.
    Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 11

Question 3.
Explain the wheel-and-axle arrangement in brief. How does the handle of a bicycle work for this arrangement?
Answer:
Wheel-and-axle arrangement consists of two cylinders of different diameters joined together such that if one is made to rotate, the other also rotates. The axle is a cylinderical rod fixed to the centre of a circular disc-like object called the wheel. This machine acts as a speed multiplier device. In riding a bicycle, when we apply force on the wheel (by pedal), the fixed axle rotates with it easily. This force that turns the axle produces a much larger movement of the wheel.
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 12

Question 4.
What is a wedge ? Explain the principle on which it works by giving suitable examples.
Answer:
A wedge is a double inclined plane such that the two sloping surfaces taper to form either a sharp edge or a pointed edge. Examples : A knife, an axe, a chisel. In some special cases, the number of inclined planes used can be more than two as well. In such cases, the sloping surfaces generally taper to form either a very sharp or a pointed edge to split or pierce materials. Pins, nails and needles are examples of pointed wedges. The front end of a boat is shaped like a wedge so that it can easily cut across the flowing water. The wedge works on a principle of an inclined plane.

Question 5.
What is an inclined plane ? What is the use of an inclined plane ?
Answer:
An inclined plane is a rigid sloping surface over which heavy loads can be raised or lowered to a certain height or depth. The mechanical advantae of an inclined plane is the ratio of the length of the plank to the vertical height of the load raised. Its value is greater than one. Therefore, an inclined plane acts as a force multiplier. Thus, it can be used to lift heavy loads.

Example : If a heavy box needs to be loaded on a lony, it is far easier to push it over an inclined plane than to lift it up. Steeper the inclined plane, greater will be the effort required to push up the load. Sloping ramps, flyovers, roads on hills and staircases are all examples of inclined planes.

F. Give reasons for the following.

Question 1.
Machines arc able to make our work convenient.
Answer:
Machines help us to perform the same amount of work with much less effort than if we did the work manually. They also make our work faster and easier by multiplying the speed or the force applied.

Question 2.
The efficiency of a machine is always less than 100%.
Answer:
Efficiency of a machine is always less than 100% as output energy is always less than the input energy, because some energy is lost to overcome friction.

Question 3.
The front end of a boat is shaped like a wedge.
Answer:
The front end of a boat is shaped like a wedge so that it can easily cut across the flowing water.

G. Solve the following numerical problems.

Question 1.
The length of a lever is 2 m. Calculate its mechanical advantage if the fulcrum is situated at a distance of 40 cm from the effort.
Answer:
Length of the lever = 2m = 200 cm
Length of the effort arm = 40 cm
Length of the load arm = 200 cm – 40 cm = 160 cm
Mechanical advantage = ?
We know that,
Mechanical advantage =  Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 13
MA = \(\frac{40 \mathrm{~cm}}{160 \mathrm{~cm}}\) = 0.25

Question 2.
The length of the load arm of a lever is 6 m long and the effort arm is 3 m long. What is the effort required to lift a load of 40 N ?
Answer:
Length of the load arm = 6 m
Length of the effort arm = 3 m
Load = 40N
Effort = ?
We know that .
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 14
By putting values, we get
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 15

Question 3.
Calculate the mechanical advantage of a crowbar of length 240 cm if its fulcrum is situated at a distance of 40 cm from the load.
Answer:
Length of crowbar = 240 cm
Length of load arm = 40 cm
Length of effort arm = 240 cm – 40 cm = 200 cm
Mechanical Advantage = Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 16
\(\frac{200 \mathrm{~cm}}{40 \mathrm{~cm}}\) = 5

Question 4.
What effort will be required to lift a load of 500 N by a single movable pulley ? [Hint : Mechanical advantage of a single movable pulley is two],
Answer:
Load = 500 N
Mechanical advantage (MA) = 2
of a single movable pulley
Effort = ?
We know that,
MA = Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 3
⇒ Effort = \(\)\frac{500}{2}latex] N = 250 N

H. Draw diagrams of the following.

Question 1.
A class II lever
Answer:
Class II lever –
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 18

Question 2.
A screw
Answer:
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 20
A screw

Question 3.
A single movable pulley Ans.
Answer:
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 21

I. Solve the crossword puzzle.

Across
5. The fixed point about which a lever can rotate
6. A type of simple machine made up of an iron bar
7. A type of machine formed when two inclined planes are put together
Down
1. A circular disc that can rotate freely about its axle
2. The force applied on a lever
3. A type of machine made up of a cylinderical rod with spiral threads.
4. The cylinderical rod fixed to the centre of a wheel
Answer:
Living Science Physics Class 6 ICSE Solutions Chapter 7 Simple Machine - 22

Living Science Physics Class 6 ICSE Solutions

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