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.
| 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.
| 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
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
You’re told to measure the mass of a marble using the CGS system. What unit(s) will your measurement be in?
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?
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?
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:
grams
The unit of mass in the CGS system is the gram.
seconds
The unit of time in the MKS system is the second.
newtons
The unit of force in the MKS system is the newton.
ergs
The unit of energy in the CGS system is the erg.
