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Scalar and vector quantities


You already know: everything that can be measured is called physical greatness. Time, mass, length, area and temperature are examples of quantities that we can understand from their values ​​and from the units of measurement in which these values ​​are expressed.

Consider the following situation:

You and your family left for the beach and halfway after an hour, stopped for a snack and after another hour arrived at the beach.

What was the total time since you left home until you reached the beach?

- The answer leaves no doubt: they will answer that the time was two hours.

However, some physical quantities are not well defined when we report only their value associated with a unit.

Think of another situation:

Two people push the same box, which is standing still. These people make strength of the same intensity.

What will happen to the box?

- You'll get it right if you answer that depends. If both people push the box in the same direction, it will move in that direction. However, if one person pushes the box in one direction and the other pushes it in the opposite direction, both forces being equal, the box will probably not move out of place.

Why doesn't the result of the two-push action depend on just how intense they were?

- The answer is that the push, ie the force applied to the box, is a Vector greatness.

What is vector greatness?

To answer this question, some concepts need to be defined.

The value of a physical quantity is called intensity of a physical greatness. Intensity is always a positive value. Some physical quantities have the characteristic of being vertical, horizontal and inclined to the horizontal or vertical, and this feature is called direction.

For each direction there is the possibility of two senses. For example, a horizontal push can be left or right. A vertical push can be up or down.

Quantities that need, in addition to their value associated with a unit, direction and meaning to be fully determined are called Vector quantities.

Examples of vector quantities are: the strength, speed, acceleration and position of a body.

The quantities that only need one unit value to be fully determined are called scalar quantities. Examples of scalar quantities are: the time, mass, length, area and temperature.

The vector quantities are represented by oriented segments, as shown below.

Scalar quantities: are fully defined with their value associated with a unit.