Units of Measurement
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📚 Units of Measurement
(in simple terms)
2- 🎯 Take the Practice Quiz( Test your understanding )
What You'll Learn
📖 1 - What is a Unit of Measurement?
To be able to measure a quantity, it is necessary to define a unit for that quantity. In fact, a unit is a specific portion of a quantity that we use to compare the quantity.
Let's give an example. Suppose we want to measure the length of a board. For this, we use a one-meter rod. Here, the length of the board is the quantity, and that one-meter rod we selected is the unit. The act of comparing the board with the rod is called measurement. Three well-known units that are most commonly used in daily life are the units of time (second), length (meter), and mass (kilogram).
📖 2 - Why should the unit of measurement be standard?
The number obtained from measurement must be expressed with an appropriate unit. In the previous example, consider two scenarios. In the first scenario, assume the length of the board is 5 times the length of the rod. In the second scenario, we choose a smaller rod; the length of the board could be, for example, 500 times the length of the rod (see the video).
This shows that the unit needs to be standard. That is, the same number should be obtained everywhere in the world. For example, one person says the distance from Earth to the Sun is 150 million. Another says it is 93 million. Both numbers are correct, provided the first is in kilometers and the second in miles. We conclude that: firstly, having a unit is essential, and secondly, it must be chosen as a standard so that others (all over the world) understand what we mean. This is why the International System of Units (SI) was established.
💡 notice:
- The chosen unit must be appropriate for the quantity itself. For example, length cannot be expressed in seconds (this point is simple but can sometimes cause mistakes. Its importance becomes fully apparent in topics like magnetism, electricity, etc.).
- Every measurement consists of two parts: the first part is the measured number, and the second part is the appropriate unit. For example, when we say an object's mass is 5 kilograms, we have expressed both parts. The first part is the number 5, and the second part is the unit kilogram.
📖 3 - What are the Characteristics of a Unit?
For a unit to be standard and useful, it must have certain characteristics:
- It must be constant and not change. For example, a spring cannot be used as a unit of length because its length is not constant. This is why a human handstrong is not suitable for this purpose, as people's hands have different sizes.
- It must be accessible so that everyone can use it; in other words, it can be replicated. For example, the unit of length, the meter, is a bar made of platinum and iridium. This bar is kept in France. Accurate copies of this unit have been sent to all countries. In this way, it becomes accessible to everyone.
- It must be possible to determine it with high precision so that precise experiments can be designed. For example, consider nanoparticles; their dimensions are very small (on the order of one billionth of a meter). To express the dimensions of these particles and even smaller ones, we need to be able to apply the unit with whatever precision is required for the measurement (some books do not mention the third point).
✏️ example 1:
Determine whether the following statements are true or false:
- With the help of unit we can compare the measurement results of a quantity with each other.
- All quantities have unit.
- A quantity can have different unit
✅ answer:
- True. In fact, this is the very reason for the existence of units. For example, the speed of one car is 50 meters per second. The speed of another car is 60 meters per second. These two can be easily compared.
- False. Because some quantities are expressed as a single number, such as the coefficient of friction or the refractive index of a transparent material. For example, we say the coefficient of friction between two surfaces is 0.2. That means it has no unit.
- True. For example, we express length in meters, but in some countries it is expressed in feet.
✏️ example 2:
Determine whether the following statements are true or false.
- The feeling of cold is a quantity.
- The results of different measurements of a quantity are the same.
✅ answer:
- The feeling of cold is not a quantity because it cannot be measured. Note that the degree of hotness or coldness of an object is a quantity because it can be measured with a thermometer. But here we are talking about the feeling of cold, which is related to human tactile sense. Sensation is not measurable.
- The results of different measurements of a quantity may not be the same. For example, the distance from Earth to the Sun may be expressed in miles or meters, which are not the same number. In this example, the quantity is the same, but the units are different(Discussion of approximation and error later).
📝 Practice Quiz
units-of-measurement
Frequently Asked Questions
📌 What is a unit?
It is a specific amount of a quantity that we use to compare the quantity.📌 What are the most important characteristics of a unit?
It must be reproducible, not change, and be precise.We Value Your Feedback
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