Lab 1: Measurement, Precision, and Accuracy

Physics, like other fields of science, is based on watching what happens and doing experiments. Scientists use many kinds of measurements in physics, including length, volume, mass, and temperature. To make good measurements, you need to understand two important ideas: accuracy and precision.

Imagine you use a ruler to measure a piece of string that is marked as 30.48 centimeters (or 0.3048 meters) long. Accuracy means how close your measurement is to the real, correct value. If you measure the string three times and all three measurements are very close to 30.48 cm, your measurements are accurate.

Precision means how close a group of repeated measurements are to each other — in other words, how much they spread out. Precision looks at the range between measurements and whether you keep getting similar results. For example, if your measurements of the string don't change very much between tries, they are precise.

In this lab you will learn:

• How to measure volume using the displacement method
• How to measure mass using a triple beam balance, a spring scale, and an electric balance
• How to measure distance using rulers, meter sticks, and string

Activity 1: Measuring Volume

Volume is the amount of space that something takes up, or the amount of space inside a container. In this activity, you will measure the volumes of three objects (with known volumes) using a graduated cylinder — a container marked with measurement lines.

You will also learn the displacement method. This is a way to measure volume by placing an object into a container that holds a known amount of water. When the object goes underwater, the water level rises. How much the water level rises tells you the volume of the object. This method works well for objects that have odd shapes, making it hard to measure their length, width, and height directly.

When you take a measurement, you record significant figures. These are the numbers you can read directly from your measuring tool, plus one extra digit that you estimate. To figure out how many significant figures a measuring tool can give you, look at how finely it is marked — this tells you which digits you know for certain.

Here are the rules for counting significant figures:

• Nonzero digits (1–9) always count as significant.
• Zeros count as significant if they are between two nonzero digits.
• Zeros at the end of a number, like in 1000, do not count as significant — unless they come after a decimal point, like in 2.00.
• Zeros at the beginning of a number, like in a decimal such as 0.005, do not count as significant.