Reflection

concept of density

Vernier callipers

The Role of Units Physicists, like other scientists, make observations and ask basic questions. For example: how big is an object? How much mass does it have? How far did it travel? To answer these questions, they make measurements with various instruments (e.g., meter stick, balance, stopwatch, etc.). The measurements of physical quantities are expressed in terms of units, which are standardized values. For example, the length of a race, which is a physical quantity, can be expressed in meters (for sprinters) or kilometers (for distance runners.) Without standardized units, it would be extremely difficult for scientists to express and compare measured values in a meaningful way. Distances given in unknown units are maddeningly useless. All physical quantities in the SI system of units are expressed in terms of combinations of seven  fundamental physical  units, which are units for: length, mass, time, electric current, temperature, amount of a substance, and luminous intensit...

There are two kinds of forces, or attractions, that operate in a molecule— intramolecular  and  intermolecular . Let's try to understand this difference through the following example. Figure of towels sewn and Velcroed representing bonds between hydrogen and chlorine atoms We have six towels—three are purple in color, labeled  hydrogen  and three are pink in color, labeled  chlorine . We are given a sewing needle and black thread to sew one hydrogen towel to one chlorine towel. After sewing, we now have three pairs of towels: hydrogen sewed to chlorine. The next step is to attach these three pairs of towels to each other. For this we use Velcro as shown above. So, the result of this exercise is that we have six towels attached to each other through thread and Velcro. Now if I ask you to pull this assembly from both ends, what do you think will happen? The Velcro junctions will fall apart while the sewed junctions will stay as is. The attachment created by Velcro...