In most physics experiments, we need to make precise measurements. Many accurate, and sensitive instruments have been developed to make measurements of various physical quantities. In this experiment, you will use a meterstick, a vernier caliper, and a micrometer caliper to measure length; a balance to measure mass; and a stop watch to measure time.

Most of the readings in this experiment will be made using the "cgs" system of unit, that is centimeter (cm) for length, gram (g) for mass, and second (s) for time. Some length measurements will also be made by using millimeter (mm) as the unit.

Measurement of Length


Measurement of Mass
In physics, mass of an object represents the quantitative measure of the inertia of the object. Inertia can be thought of the reluctance of the object to have its state of motion changed; in other words, it tends to remain at rest, or if in motion, it tends to keep in motion with a constant velocity. It is important to note that mass of an object is not equivalent to its weight. Weight of an object represents the gravitational force acting on it.

The balance you will use in this experiment consists of a double beam with scales etched on each beam (the lower beam reads up to 200 grams in 10-g divisions, and the upper beam reads up to 10 grams in 0.1-g divisions), a pointer, and two pans attached to either side of the beam, so that the beam and the pans swing freely. The pans should be balance when they are empty, and the pointer should rest on the zero mark etched on the scale located midway between the two pans. An adjustment nut at the end of the beams can be used to calibrate the balance.

To measure the mass of an object, place the object on the left-hand pan of the scale. Slide the movable permanent mass attached to the lower scale until the right-hand side of the balance moves down. This means the mass is too large. Move the permanent mass back one unit on the lower scale such that the balance moves upward, indicating that there is not enough mass to balance the scale. Now move the smaller permanent mass on the top scale to the right until the beam is balanced. The mass of the object is then equal to the sum of the masses indicated on each scale.

The maximum mass that can be measured directly in this fashion is 210 grams. For objects that are over 210 g, a known mass (chosen from a mass set) can be placed on the right-hand pan of the scale (see the figure above). After balancing the scale, the mass of the object is then the sum of the masses indicated on each scale plus the additional mass on the right-pan.


Measurement of Time
A digital timer (a stopwatch) will be used to measure time interval. The timer displays the elapsed time in minutes, seconds, and hundredths of a second. The last digit displayed is the first doubtful figure. For instance, the time displayed is 12.56 s; the first uncertain figure in this reading is the "6" in the hundredths place.