Mass means the amount of matter in an object. Matter is something that can be felt physically. In general, mass is related to the size of the object, but this is not always the case. For example, a balloon may be larger than another object, but have less mass. There are several methods you can use to calculate mass.
Step
Part 1 of 3: Determining Mass from Density and Volume of an Object
Step 1. Find the object's density
Specific gravity is an indicator of the density of matter in an object. Each material has its own specific gravity which can be found on the internet or textbooks. The scientific unit for specific gravity is the kilogram per cubic meter (kg/m3), but you can also use grams per cubic centimeter (g/cm3) for smaller objects.
- Use this formula to convert specific gravity units: 1,000 kg/m3 = 1 g/cm3
- On the other hand, the specific gravity of a liquid is often expressed in kilograms per liter (kg/l) or grams per milliliter (g/ml). These units are equivalent; 1 kg/l = 1 g/ml.
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Example:
diamond has a specific gravity of 3.52 g/cm3.
Step 2. Calculate the volume of the object
Volume is the amount of space occupied by an object. Express the volume of a solid in cubic meters (m3) or cubic centimeters (cm3), and the volume of fluid in liters (l) or milliliters (ml). The volume formula is determined by the shape of the object. Read this article for general noun formulas.
- Use the same units as those listed in specific gravity units.
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For example:
because we express the specific gravity of diamonds in units of g/cm3, we must express the volume of the diamond in cm3. Let's say the volume of our diamond is 5,000 cm3.
Step 3. Multiply the volume and density of the object
Multiply the two numbers, and you'll get the mass of the object. Pay attention to the units of measure during the calculation, and you will get the units of mass (kilograms or grams) in the final result.
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For example:
we have a diamond with a volume of 5,000 cm3 and specific gravity 3.52 g/cm3. To find the mass of a diamond, do the calculation of 5,000 cm3 x 3.52 g/cm3 = 17,600 grams.
Part 2 of 3: Calculating Mass in Other Physics Problems
Step 1. Determine the mass with the force and acceleration
Newton's second law of motion states that force is equal to mass times acceleration, or F = ma. If you know the resultant force on an object and its acceleration, you can change this formula to calculate mass to: m = F / a.
Force is expressed in units of N (newtons), which can also be written (kg * m)/ s2. Acceleration is expressed in units of m/s2. When calculating F/a, the units of force and acceleration are mutually exclusive so that the answer is expressed in kilograms (kg).
Step 2. Understand the difference between mass and weight
Mass is the amount of matter in an object, which will not change unless one part of the object is cut or added. Weight is a measure of the effect of the gravitational force on the mass of an object. If you move an object to a place with a different gravitational force (say from the earth to the moon) its weight will change, but its mass will not.
However, an object of greater mass will weigh more than an object of less mass if it is affected by the same gravitational force
Step 3. Calculate the molar mass
While working on a chemistry assignment, you may come across the term "molar mass." Molar mass is a relative concept, which measures not one object, but one mole of a compound. Here's how to calculate it in most sample questions:
- For an element: find the atomic mass of the element or compound you are calculating. This is the atomic mass unit or amu. Multiply by the molar mass constant, 1 g/mol, so that it can be expressed in standard molar mass units g/mol.
- For a compound: add up the atomic masses of the atoms making up the compound to get the total amu for the molecule. Multiply this total by 1 g/mol.
Part 3 of 3: Measuring Mass with a Balance
Step 1. Use a three-arm balance
This balance is widely used to calculate the mass of objects. This balance has three arms equipped with weights. The weights on the balance arm can be shifted so that you can measure the mass of the object.
- This three-arm balance is not affected by the force of gravity, so it can provide an accurate measure of mass. The way it works is by comparing the mass of a known object with the mass of the object being sought.
- The middle balance arm has a scale of 100 g, while the back arm has a scale of 10 g, and the front arm can read from 0 to 10 g. The weights on the arm are located at one point.
- You can measure the mass of an object accurately using this balance. The measurement error on the three-arm balance is only 0.06 g. Imagine this balance sheet working like a seesaw.
Step 2. Slide the three weights up to the left end of the arm
Slide everything while the balance plate is still empty, so the number that reads is zero.
- If the marker on the right end of the arm is not parallel to the equilibrium line, you must calibrate the balance by turning the screw on the lower left side of the balance plate.
- You should do this step to make sure the empty balance plate weighs 0.000 g so that it doesn't affect the reading of the results obtained. The weight of the balance plate is called the tare.
- You can also turn the dial under the dish in or out until it reads zero. Place the object to be measured on the balance plate. Now, you are ready to determine the mass by sliding the weight.
Step 3. Slide the weights one by one
First, slide the weight on the 100 g arm to the right. Continue sliding until the marker is below the equilibrium point. The scale on the balance arm is calculated from the left side stating the mass of the object in units of hundreds of grams. Swipe from one point to another.
- Slide the weight on the 10 g arm to the right. Keep sliding until the marker is below the equilibrium point. The scale on the balance arm is calculated from the left side stating the mass of the object in tens of grams.
- The front arm of the balance is not marked with a scale. You can shift the weights to any side. The number that is read on the arm represents the mass of the object in grams. The bold lines between the numbers on the arms represent tenths of a gram.
Step 4. Calculate the mass of the object
Now, you can calculate the mass of the object on the balance plate. You only need to add up the numbers that are read on the three arms of the balance.
- Read the front arm like reading a ruler. You can read it to the nearest half line.
- For example, let's say you measure the mass of a can of soda. If the back arm reads 70 g, the middle arm reads 300 g, and the front arm reads 3.34 g, the mass of the can of soda is 373.34 g.
Tips
- The symbol for mass is m or M.
- You can use an online calculator to calculate mass if you already know the volume and specific gravity.
