Measurements in Physics

Fundamental Units• The SI system (AKA the System International or

the metric system

• There are 7 fundamental units:1. Meter (m)- measures distance2. Kilogram (kg) – measures mass3. Second (s) – measures time4. Ampere (amp) –measures electric current 5. Kelvin (K) – measures temperature6. Mole (mol) – measures chemical quantities7. Candela (cd) – measures light intensity

Derived Units• Derived units are combinations of two or more

fundamental units. • Examples of derived units:

1. Newton- Measures force2. Hertz –Measures frequency3. Joule – measures energy4. Coulomb – measures charges5. Volt – measures potential difference6. Watt – measures power7. Ohm – measures resistance

Why Use the SI Units?• Unlike our common measurements, the

metric system is based on multiples (or powers of) 10.

Scientific Notation• The conversions and expression of measurement

sin the metric system are made easy by Scientific Notation

• The format is always: #.### x 10#

o Note: The number before the decimal cannot be a zero, it must be a 1-9 digit!

o Example 3.0x108

• The power of the ten is referred to the magnitude of the numbero Positive exponents are large numberso Negative exponents are small numbers

Converting to and from

• Simply count decimals!

Q. Write in decimal notation: 3.6x1012

A. Since the power is positive, I know that the number has to get larger. The magnitude is 12, so I have to move the decimal 12 places to the right.

Con’tQ. Write in decimal notation 4.36x10-11 R. Since the power is negative, I know that the

number has to get smaller. The magnitude is 11, so I have to move the decimal 11 places to the left.

Con’tQ. Write in scientific notation 300000000

R. Since this is a large number I know the power of ten will be positive. So I count the number of times I move the decimal over so that just one nonzero number is in front of it and make this number the positive power of ten.

Con’tQ. Write in scientific notation: 0.00000000578

R. Since this is a small number, the magnitude of ten must be negative. So I count the number of places I move the decimal until one number is in front of it, and make this the negative power of ten.

Try- Your turn to practice

Tough- This is hard, but you can

do it!

Let’s Practice…

Significant figures• One benefit of scientific notation, is it allows

numbers to represent only the significant figures.• To determine the number of significant figures:

o Is the decimal point absent or present?

Teacher- Let me model to help

you out.

Together- Volunteers?

Try- Your turn to practice.

Tough- This is hard, but you can

do it!

Let’s Practice…

Pre-Fixes• Instead of writing out the power of ten (like we

just did), scientists often use prefixes on the base unit to establish the magnitude of the measurement.

• The prefixes you need to know are listed on page 1 of your reference table.

• These prefixes also signify the order of magnitude of a measurement (by looking at the notation on our chart)

Another word for “order of magnitude”

• To convert between scientific notation and prefixes:1. Put the number in scientific notation2. Find the power of ten from the notation on the

chart3. Rewrite the original number replacing the power

of 10 (so the x10#) with the prefix.4. Don’t forget to use the correct base units!

• To convert between prefixes and scientific notation (or powers of 10)1. Make sure your units have a prefix.2. Find the prefix on the chart.3. Rewrite the original number replacing the prefix

with the power of 10 notation from the chart.4. Don’t forget to use the base units (that no longer

have the prefix)

Converting Formats

Let’s PracticeQ. Write in standard units: 19 KJA. The prefix we have is a K. Looking on the chart,

the notation of K is x103, so I rewrite the 19, replace the K with x103 and put on my base unit of J. My answer is 19x103 J

Let’s PracticeQ. Write with a prefix : 6.9 x 10-9 mA. The notation we have is x 10-9 , and looking at

the chart that is the “nano” prefix. So I rewrite the number 6.9 and preplace the power of ten with the symbol for nano so my answer is 6.9 nm.

Teacher- Let me do another one

Together- Let’s try one together

Try- Your turn to practice

Tough- This is hard, but you can

do it!

Let’s Practice…

Converting Between Prefixes

• We can use the following chart:

• Easy trick: The number of zeros correspond to the power of ten for the prefix!

• Another hint: when your going from big to small prefixes multiply. When you go from small to big prefixes divide.

Convert Between Units

Q. Complete the following conversionsTeacher: 350 µg = _______ mg

Together: 20 km = _______ m

Try: 850 l = _______ ml

Try: 8 cm = _______ m

Try: 3 mg = _______ g

Tough: 3x108m = _____________km

Approximating Size• Now that you practiced measuring the metric

system, you will often be asked to approximate the size of something.

• Based on what you learned fill in the following chart to help you remember:

The measurement of…

Is approximately….

one shoulder to the opposite finger tip

100 m (remember this equals 1 m)

10-1 m

10 -2 m

100 m

1 kg

1 g

100 kg

Performing Operations• It is easy to perform mathematic

operations as long as we can use our calculators!

Math Review• Can you successfully…?1. Solve for a specific variable2. Perform exponent operations 3. Solving for the missing side of a right triangle4. Find an angle in a right triangle

Find out by doing each section of the worksheet at the corresponding station. Once you are done, get your answers checked. Based on what you did incorrectly and your conversation with Miss Shea, fill out page 8 of your notes.Notice: If you don’t have quality notes written for EACH section, you will receive a zero for today’s work!