Properties of Matter Study Guide

Updated on Sep 27, 2011


There is a field of physics that studies the mechanical behavior of rigid objects, The objects of study were found in a solid state, they were rigid (of fixed shape and volume), and they were acted on by forces, In this lesson, we will study different phases: in particular, liquid and gas phases, And we will define basic concepts such as density and pressure, We will also study why some objects float and others don't, and how pressure spreads in a fluid.

Phases of Matter

The previous chapters analyzed one of the states that matter can be found in—the solid phase, At an atomic level, the solid state is defined by a clear structure where atoms and ions occupy rather fixed positions. Solid objects have a clear shape and volume. Although they are characterized by some elastic properties, it takes different strengths to change the shape of a solid object. This strength depends on the internal bonding of the particles.

We will now look at some basic characteristics of two other phases of matter—the liquid phase and gas phase. Liquids and gases together are also known as fluids.


Analogy is a powerful tool in the world of science. Remember, we defined forces that deal with mechanical interaction and cause static and dynamic effects. We also defined torque as the anaJog of force, in cases where rotational motion (instead of linear motion) was a possible outcome of interaction. The objects of interaction were solid objects of definite shape. In the case of liquids, the shape is no longer a constraint: Depending on the container, a liquid can change its shape and its effect on the surrounding medium. What do we mean by that? Imagine this case: two liters of water (remember, liter is a unit for volume) divided equally into two containers of shapes as shown in Figure 10.1. Do you think they have the same interaction with the surface of support?


The answer is no because although each liter of water will act with the same weight on the surface of support, but the area is different in the two cases. If a person wears sneakers and then changes into high heels, the mark left on a soft asphalt will be different. It will be deeper when the person is on heels even though the weight of the person did not change. Although the weight was the same, the surface area of support is smaller with the heels, and therefore, the effect on the support surface area is larger. The quantity measuring the force and the effect on the surface on which it acts is called pressure.

There are many units for pressure, but the SI unit is Different fields of application deal with different ranges of pressure and with different measuring instruments. Therefore, applications have imposed different scales. Some of the most used scales are the pascal (Pa), the milibar (mb), the inch of mercury or milimeter of mercury (mmHg), and the pound per square inch (PSI).


Pressure measures the force exerted perpendicularly per unit area.

If the force is due to the weight of the liquid, then the definition above becomes:


Units of Pressure

1 atm = 101,325 N/m2

1 mb = 1 hPa (hecto pascal) = 100 Pa

1 in Hg = 33.8639 mb = 3,386.39 Pa

1 mmHg = 133.32 Pa

1 PSI = 6.895 kPa


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