Measuring Length with a Metric Ruler

You’ve probably been using a ruler to measure length since you were in elementary school. But you may have made most of the measurements in English units of length, such as inches and feet. In science, length is most often measured in SI units, such as millimeters and centimeters. Many rulers have both types of units, one on each edge. The ruler pictured below has only SI units. It is shown here bigger than it really is so it’s easier to see the small lines, which measure millimeters. The large lines and numbers stand for centimeters. Count the number of small lines from the left end of the ruler (0.0). You should count 10 lines because there are 10 millimeters in a centimeter.

Q: What is the length in millimeters of the red line above the metric ruler?
A: The length of the red line is 32 mm.
Q: What is the length of the red line in centimeters?
A: The length of the red line is 3.2 cm.

Measuring Mass with a Balance

Mass is the amount of matter in an object. Scientists often measure mass with a balance. A type of balance called a triple beam balance is pictured in Figure below. To use this type of balance, follow these steps:

1. Place the object to be measured on the pan at the left side of the balance.
2. Slide the movable masses to the right until the right end of the arm is level with the balance mark. Start by moving the larger masses and then fine tune the measurement by moving the smaller masses as needed.
3. Read the three scales to determine the values of the masses that were moved to the right. Their combined mass is equal to the mass of the object.

Q: What is the maximum mass this triple beam balance can measure?
A: The maximum mass it can measure is 610 grams (500 grams + 100 grams + 10 grams).
Q: What is the smallest mass this triple beam balance can measure?
A: The smallest mass it can measure is one-tenth (0.1) of a gram.

To measure very small masses, scientists use electronic balances, like the one in the Figure below. This type of balance also makes it easier to make accurate measurements because mass is shown as a digital readout. In the picture, the balance is being used to measure the mass of a white powder on a plastic weighing tray. The mass of the tray alone would have to be measured first and then subtracted from the mass of the tray and powder together. The difference between the two masses is the mass of the powder alone.

Measuring Volume with a Graduated Cylinder

At home, you might measure the volume of a liquid with a measuring cup. In science, the volume of a liquid might be measured with a graduated cylinder, like the one sketched below. The cylinder in the picture has a scale in milliliters (mL), with a maximum volume of 100 mL. Follow these steps when using a graduated cylinder to measure the volume of a liquid:

1. Place the cylinder on a level surface before adding the liquid.
2. After adding the liquid, move so your eyes are at the same level as the top of the liquid in the cylinder.
3. Read the mark on the glass that is at the lowest point of the curved surface of the liquid. This is called the meniscus.

Q: What is the volume of the liquid in the graduated cylinder pictured above?
A: The volume of the liquid is 67 mL.
Q: What would the measurement be if you read the highest point of the curved surface of the liquid by mistake?
A: The measurement would be 68 mL.

This text was adapted from CK12.com. It is licensed under the Creative Commons (CC BY-NC 3.0) 

When measuring it is important to consider if your measurements are accurate and/or precise. For more information see the next blog post.

Accuracy

The accuracy of a measurement is how close the measurement is to the true value. If you were to hit four different golf balls toward an over-sized hole, all of them might land in the hole. These shots would all be accurate because they all landed in the hole. This is illustrated in the sketch below.

Precision

As you can see from the sketch above, the four golf balls did not land as close to one another as they could have. Each one landed in a different part of the hole. Therefore, these shots are not very precise. The precision of measurements is how close they are to each other. If you make the same measurement twice, the answers are precise if they are the same or at least very close to one another. The golf balls in the sketch below landed quite close together in a cluster, so they would be considered precise. However, they are all far from the hole, so they are not accurate.

Explore More

Review the concepts of accuracy and precision. Then play the dart game until you obtain scores that are both accurate and precise.