Fundamental Quantities

                  There are 7 fundamental quantities, namely: length, mass, time, temperature, electric current, amount of substance, and luminous intensity. 

Length.  In daily life, length is used for measuring distance, thickness of a book, etc. In science length represents the distance between two points, for instance the length of the side of a triangle is the distance between two corners of the triangle. The SI  of length is meter (m). 

Mass. The amount of materials in the substance is called mass. Mass is not the same as weight. The mass is determined by the contained materials and fixed state although the object’s position changes. Weight depends on the position of the object on the earth and is affected by the gravitational force. In SI, mass uses fundamental unit of kilogram (kg) and is measured with lever balance while the unit of weight is Newton (N) and is measured with spring balance. 

Time. Time is the duration between two events. For example, daylight is between the sunrise and sun set. Life time is between birth and death. The SI unit for time is second (s). 

Temperature. Fire is hot but ice is cold. A hot object is said to have high temperature, but a cold object has low temperature. Thus temperature shows the degree of hotness and coldness of an object. The common measuring tool for temperature is a thermometer. 

     Questions:

1.      How many types of fundamental quantities are there? What are they?

2.      Give examples of objects around us that have length!

3.      What is ‘mass’?

4.      What is the difference between ‘mass’ and ‘weight’?

5.      What is ‘time’?

6.      What is ‘temperature’?

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Definition of Measurement

Measuring is an important scientific skill.  To measure the length of a table using a book, you compare the length of the table with the length of the book, and the book is used as a unit. Length is one of base quantity.

The result of measurement is useful if it uses a standard of measurement. It is an agreed unit of measurement with fixed value. A book used as a unit of measurement is not standard because there are different sizes of books.

Measuring systems. People used to use their body as units of measurement such as fathoms, span, foot, and step. But those units are not standard and can cause difficulty in communicating them.

You may hear people use units of measurement such as: gallon for water, yard for thread, and inch for pipe. Those units are examples of units in the British system.  After the 1700 some scientists used measuring system called the metric system. Then, in 1960 the metric system was used and officially called the international system or SI units (Le Systeme International d'Unites). In the SI, each base quantity has a unit, for example, meter for length, second for time, and kilogram for mass.

Questions:

1. Books are not standard measurement. Why?
2. What parts of body did people use to use as units of measurement?
3. What is a unit for ‘time’?
4. What is a unit for ‘mass’?
5. “Those units are examples of units in the British system.” What does the underlined word refer to?
6. What measuring system did scientist use after the 17^th century?

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The Definition of Heat

       What will happen if you touch a cool wall with your hands for five minutes? Your hands will feel cooler and the parts of the wall that you touch will be warmer. The temperature of your hands decreases while the temperature of the wall increases. The heat energy flows from your warm hands to the cool wall. 

   The energy flowing from an object with higher temperature to another object with lower temperature is called heat. The heat always flows from an object with higher temperature (hot) to another object with lower temperature (cool). You cannot feel cool if you are standing near a fire. 

            Heat is measured in unit of calorie. One calorie is defined as the amount of the heat energy required to raise the temperature of 1 ^oC of  1 gram of water. It will take 500 calories to heat 500 grams of water from 20 ^oC to 21 ^oC. In International System, heat is measured in unit of Joule. One Calorie is equal to  4.184 Joule, and it is frequently rounded up to  4.2 joule.

            Your body converts some food you eat into heat energy. The heat energy provided by the food is measured in Calorie (Kilocalorie). We use kilocalorie for the food to simplify the expression. One kilocalorie (kcal) of food is equal to 1000 calories.

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