In classical physics, mass identifies the amount of matter present in a given object. By matter we mean everything that can be physically touched, that is, that has a physical consistency, weight and is subject to forces present in nature. Mass is generally related to the size of an object, but this relationship is not always true. For example, a balloon could be much larger than another object, but have a significantly smaller mass. There are several methods to measure this physical quantity.
Steps
Method 1 of 3: Calculate Mass Using Density and Volume
Step 1. Identify the density of the object under examination
The density of an object or substance measures the concentration of matter present in a unit of volume. Each material or substance has its own density; you can perform a simple online search or you can consult a physics or chemistry manual to find out the density of the material of which the object you are studying is made. The unit of measure for density is the kilogram per cubic meter (kg / m3) or the gram per cubic centimeter (g / cm3).
- To convert the measurements of these two units, you can use this equality: 1000 kg / m3 = 1 g / cm3.
- The density of liquids is often measured in kilograms per liter (kg / l) or in grams per milliliter (g / ml). These two units of measurement are equivalent: 1 kg / l = 1 g / ml.
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Eg:
diamond has a density of 3, 52 g / cm3.
Step 2. Calculate the volume of the object under examination
The volume identifies the amount of space occupied by an object. The volume of a solid is measured in cubic meters (m3) or in cubic centimeters (cm3), while the volume of liquids is measured in liters (l) or in milliliters (ml). The formula for calculating the volume of an object depends on its physical form. Refer to this article to calculate the volume of the most common geometric solids.
- Express volume using the same unit of measurement used to express density.
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Eg:
since the diamond density is expressed in g / cm3, its volume should be expressed in cm3. We therefore assume that the volume of the diamond we are studying is 5000 cm3.
Step 3. Multiply the volume by the density
To find the mass of an object, multiply its density by the volume. During this operation, pay close attention to the units of measurement involved to obtain the correct one with which to express the mass (kilograms or grams).
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Eg:
we have assumed to have a diamond with a volume of 5000 cm3 with a density of 3, 52 g / cm3. To calculate its mass, we need to multiply these two values to get 5000 cm3 x 3, 52 g / cm3 = 17.600 grams.
Method 2 of 3: Calculating the Mass in Other Scientific Areas
Step 1. Determine the mass by knowing the force and acceleration
Newton's second law, relating to dynamics, states that the force is given by the mass multiplied by the acceleration: F = ma. If we know the force applied to an object and its acceleration, we can use the inverse formula to derive the mass that is: m = F / a.
Force is measured in N (newtons). A newton is also defined as (kg * m) / s2. Acceleration is measured in m / s2; therefore, when we divide the force by the acceleration (F / a), the respective units of measurement cancel each other out, expressing the final result in kilograms (kg).
Step 2. Understand what mass and weight mean
Mass defines the amount of matter present in a given object. Mass is an invariable quantity, that is, it does not change according to external forces unless a portion or part of the object is removed or more matter is added. The weight instead measures the effect produced by the force of gravity on the mass of an object. Moving the same object to places subjected to a different force of gravity (for example from the Earth to the Moon) its weight will vary accordingly, while its mass will remain unchanged.
It can therefore be deduced that an object with a higher mass weighs more than an object with a lower mass, if exposed to the same force of gravity
Step 3. Calculate the molar mass of an object
If you're struggling with a chemistry problem, you may come across the scientific term molar mass. It is a concept related to mass which, instead of measuring that of an object, measures that of a mole of a substance. Below is the method to calculate it within the most common contexts:
- Molar mass of an element: in this case refer to the atomic mass of the element or compound in question you wish to measure. This size is expressed in "atomic mass units" (the symbol is "u", but sometimes you can find it expressed in "amu" from the English "atomic mass units" or "uma" from the literal translation into Italian, but it is of two units of measurement now obsolete). Multiply the molar mass by Avogadro's constant, 1 g / mol, to express it with the standard unit of measurement that is "g / mol".
- Molar mass of a compound: adds together the atomic masses of each atom present in the compound in order to calculate the total "u" (unit of total atomic mass) of one of its molecules. When finished, multiply it by Avogadro's constant, i.e. 1 g / mol.
Method 3 of 3: Measure Mass with a Scale
Step 1. Use a laboratory balance equipped with three slide weights
It is a widely used tool for calculating the mass of an object. This scale is equipped with three measuring rods, on each of which a sliding weight is mounted. These cursors allow you to move a specific known mass along the balance rods and then to take the measurement.
- This type of scale is not affected by the force of gravity, so it measures the real mass of a given object and not its weight. This is because the principle of operation is based on comparing a known mass with an unknown mass.
- The weight of the central rod allows for increments of 100 g. The lower shaft allows a weight increase of 10 g, while the cursor of the upper shaft allows a reading between 0 and 10 g. On all measuring rods there are notches whose purpose is to facilitate the positioning of the respective cursors.
- Using this type of balance it is possible to obtain a very precise mass measurement. The error that can be made is only 0.06 g. Think of how this scale works like a rocking swing.
Step 2. Place each of the three scale sliders on the far left of each measuring rod
You must perform this step when the instrument plate is still empty; in this way, the scale should measure a mass equal to zero grams.
- If the moving indicator of the scale is not perfectly aligned with the fixed one, it means that it needs to be calibrated. To do this, you have to act on the appropriate adjustment screw that you should find under the plate, on the left side.
- This step is mandatory because it is necessary to verify that, when the pan is empty, the balance measures a mass exactly equal to 0, 000 g. This way you can be sure that the measurement of the mass you want to weigh is precise and accurate. The weight of the weighing pan or of the container in which the object to be weighed will be positioned is called "tare", hence the name of the action we have just performed, ie "tare" the measuring instrument.
- The weighing pan must also be calibrated correctly before proceeding by acting on the relative adjustment screw located exactly under the pan itself. Also in this case, the scale measurement must be zero. When finished, place the object to be weighed in the center of the weighing pan. Now, by acting on the cursors of the measuring rods, we are ready to find out the mass of the object under examination.
Step 3. Move only one cursor at a time
You must place the 100g one first by moving it to the right along its measuring rod. Keep moving the weight until the moving scale indicator drops below the fixed one. The number indicated by the position reached by the first cursor indicates hundreds of grams. Remember to move it only one notch at a time to get an accurate reading.
- Repeat this step by moving the 10g slider to the right. Again, continue until the moving scale indicator drops below the fixed one. The number that distinguishes the notch immediately to the left of the cursor represents tens of grams.
- The upper measuring rod of the scale does not have reference marks in which to position the relative cursor. In this case, the weight can assume any position along the entire length of the rod. The bold numbers on the rod measurement scale indicate grams, while the intermediate notches, present between individual numbers on the scale, indicate tenths of a gram.
Step 4. Calculate the mass
At this point, we are ready to calculate the mass of the object under examination. To do this, it is necessary to add together the three numbers measured by the relative cursors of the scale.
- Read the number on the measurement scale of each rod as if it were a ruler. To do this, refer to the left notch of the scale which is closest to the cursor.
- For example, let's say we want to measure the mass of a canned soft drink. If the slider of the lower measuring rod shows 70g, the middle one shows 300g and the top one measures 3.44g, it means that the can has an overall mass of 373.34g.
Advice
- The symbol used to refer to the mass is "m" or "M".
- If you know the volume and density of an object, you can calculate its mass using one of the many websites that offer such a service.
