 Measurements and Physics - dummies

A great deal of physics has to do with making measurements — that’s the way all physics gets started. For that reason, physics uses a number of measurement systems, such as the CGS (centimeter-gram-second) system and the MKS (meter-kilogram-second) system. You also use the standard English system of inches and feet and so on — that’s the FPI (foot-pound-inch) system. The most common measurement system in introductory physics is the MKS system.

In physics, most measurements have units, such as meters or seconds. For example, when you measure how far and how fast a hockey puck slid, you need to measure both the distance in centimeters and the time in seconds.

For reference, the table gives you the primary units of measurement in the MKS system.

MKS Units of Measurement
Measurement Unit Abbreviation
Length meter m
Mass kilogram kg
Time second s or sec
Force newton N
Energy joule J
Power watt W
Pressure Pascal Pa
Electric charge coulomb C
Electric current ampere A
Electric potential volt V
Magnetism tesla T

These are the measuring sticks that will become familiar to you as you solve problems and triumph over the math in physics. Also for reference, the next table shows the primary units of measurement (and their abbreviations) in the CGS system.

CGS Units of Measurement
Measurement Unit Abbreviation
Length centimeter cm
Mass gram g
Time second s or sec
Force dyne dyn
Energy erg erg
Power erg per second erg/s
Pressure barye Ba
Electric charge franklin Fr
Electric current biot Bi
Magnetism gauss G

## Sample question

1. You’re told to measure the length of a racecar track using the MKS system. What unit(s) will your measurement be in?

The correct answer is meters. The unit of length in the MKS system is the meter.

## Practice questions

1. You’re told to measure the mass of a marble using the CGS system. What unit(s) will your measurement be in?

2. You’re asked to measure the time it takes the Moon to circle Earth using the MKS system. What will your measurement’s units be?

3. You need to measure the force a tire exerts on the road as it’s moving using the MKS system. What are the units of your answer?

4. You’re asked to measure the amount of energy released by a firecracker when it explodes using the CGS system. What are the units of your answer?

The following are the answers to the practice questions:

1. grams

The unit of mass in the CGS system is the gram.

2. seconds

The unit of time in the MKS system is the second.

3. newtons

The unit of force in the MKS system is the newton.

4. ergs

The unit of energy in the CGS system is the erg.