Science note, calss-8, Unit-Measurement

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Science Note-Class 8

Unit-1 Measurement

Type-1 Definition

Measurement = Measurement of unknown quantity with known quantity is called measurement.  Or knowing the exact amount of an object is called measurement.

Physical Quantity = A quantity that can be measured mathematically is called a physical quantity.  For example: area, mass, time, volume, etc. 

Fundamental Unit = A unit that does not depend on other units of measurement is called a basic unit.  For example: meter, kilogram, second etc.

Derived Unit = A unit that depends on a unit of other measurements or is made up of a basic unit is called a derived unit.  Caste: Jul, Newton, Watt, Pascal, etc.

Mass = Mass of matter in an object is called mass.

1 kg mass = The lid lump made of platinum and iridium metal kept in the International Weights and Measures Department is called one kilogram mass.

Weight = The force that the earth pulls an object towards its center is called weight.

Time = The period between two events is called Time.

One Solar Day = The time it takes for the earth to rotate once on its axis is called a solar day.

One Second = One segment of 86,400 segments of a day is called a second.

S.I. unit = The international system of measurement is called S.I.  The unit is called.

C.G.S. System = A system that measures length in centimeters, mass in grams, and time in seconds is called CGS system.

F.P.S. System = The system of measuring length in feet, mass in pounds, and time in seconds is called FPS system.

M.K.S. System = The system that measures length in meters, mass in kilograms and time in seconds is called MKS system.

Type-2 Different

Distinguish the given questions:

Basic unit and derivative unit


Mass and weight 


Type-3 Numerical Problem

Mass

Convert into Gram

Example:

1. 2.5kg

Here, 2.5×1000 gram

          =2500 gram Ans.

Do yourself as given example

2. 5kg                Ans.5000 gram 

3. 24.5kg          Ans.24500 gram

4. 37.25kg        Ans.37250 gram 

5. 0.95kg          Ans.950 gram 

6. 10.11kg        Ans.10110 gram 

7. 98.234kg     Ans.98234 gram 

Time

Convert into Second

Example:

1. 6 hrs.

Here, 6×60 min 

         = 360 min

         = 360×60 sec

         = 21600 sec Ans.

2. 5 solar day

Here, 5×24 hrs. (1 solar day=24 hrs.)

         =120 hrs.

         =120×60 min 

         =7200 min 

         =7200×60 sec 

         =432000 sec Ans.

Do yourself as given example

3. 12 hrs.            Ans.43200 sec 

4. 1 solar day     Ans.86400 sec

5. 12 solar day   Ans.1036800 sec

6. 1 year             Ans.31536000 sec 

7. 9 year             Ans.283824000 sec

Weight

1. Weight of a man 40kg  If so, how much does it weigh?  (g =9.8m/s²)

Here, 

Mass of human     (m)= 40kg 

Weight of human (W)= ?

We know that,

                         W=m×g 

                             =40×9.8

                             =392 N Ans.

Weight of human(W)=392 N 

Do yourself as given example

2. What is the weight of an object weighing 90 kg? (g=9.8m/s²) Ans.882 N 

3. What is the weight of an object if its mass is 78.75kg ? (g=9.8m/s²) Ans.771.75 N 

4. Find the mass of an object with a mass of 420kg. (g=9.8m/s²) Ans.4116 N 

Type-4

1. What do you mean the weight of an object is 5kg ?

Ans. The weight of an object is 5kg which means that 5kg of 1kg is 5 times.

2. Why is the unit of time called the basic unit?

Ans. The unit of time does not depend on other units of measure, that is, it is independent, so it is called the basic unit.

3. Why is the unit of acceleration called the unit of derived ?

Ans. The unit of acceleration depends on the units of other measurements, that is, the basic units are formed together, so it is called the unit of derived.

4. Write units and symbols of different physical quantities.

Ans.


5. How many solar days in a second ? Calculate.

Ans. Here,

         1 solar day= 24 घन्टा 

                           =24×60 min 

                           =1440 min 

                           =1440×60 sec 

       1 solar day=86400 sec

Now,

        86400 sec= 1 solar day

         1 sec        = 1/86400 solar day Ans.

Very Important Questions for exam:

1. Distinguish between body and weight.  

2. Distinguish between the basic unit and the unit.  

3. What is meant by an object weighing 5kg?  

4. Why is the unit of length called the basic unit?  

5. Why is the unit of pressure called the unit of origin?  

6. S.I.  What is an S.I. unit?  

7. What is a basic unit?  Write with Example 

8. What is the unit of origin?  Write with examples.  

9. How many seconds does a saree have in a day?  

10. How many solar days are there in a second?  

11. What is physical quantity?  Write with examples.

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