Catalyst (5 min)

Complete the following calculations:1. 5.5 – 4.0 = ________2. 7.9 – 2.7 = _______________3. 4.6 – 7.0 = ___________4. 23 + 273 = ________5. X + 273 = 363, X = _________

You will need to bring a calculator tomorrow!

Catalyst (5 min)

Complete the following calculations:

1. 5.5 – 4.0 = ________

2. 7.9 – 2.7 = ________

3. 4.6 – 7.0 = ______

4. 23 + 273 = ________

5. X + 273 = 363, X = _________

1.5

5.2

- 2.4

296

90

The Metric System

SI (System International)10/5/10

Metric System

Used by every country in the world, except the USA.

Always used by scientists. Also called SI, which is French stands

for System International. Based on the number 10, so it’s

easy!

Measuring Length Length is the

distance between two points.

Basic unit = meter.

Meter = m ruler or meter

stick

Measuring Mass

Mass is the amount of matter (stuff) that makes up an object.

Basic unit = gram.(g)

Tool: scales

Measuring Volume Volume is the

amount of space contained in an object.

Base unit = Liter (L).

We measure volume with a graduated cylinder or beaker.

Measuring Temperature

Temperature is the measure of the average heat or heat energy

Basic unit= degree Celcius (°C) or Kelvin (K)

We use thermometers to measure temperature.

K = °C + 273

Let’s review our basic units!!!

Length Meter (m)

MassGram (g)

Volume Liter (L)

Temperature°C or K

We need more accuracy

We can’t measure everything with just basic units

We need prefixes!

Metric Prefixes We add prefixes BEFORE basic units to make new units

that are smaller or bigger Common prefixes from large to small:

kilo (k) = 1000centi (c ) = 1/100th milli (m) = 1/1000th

Example: kilogram (kg) = 1000 g 100 centimeters (cm) = 1 m

1000 milliliters (mL) = 1 L

Why is measurement important?

We make measurements in the lab

We use measurements to back up our conclusions

If our measurements are not accurate, our conclusions are not supported!

When is measurement important?When is measurement important?

Why does messing up the dosage of medicine cause more problems for children than adults?Children have smaller bodiesA small amount of medicine has a larger affect in a

child than in an adult

KEY POINT: When measuring, we need to be accurate and precise, or end up with some serious consequences!

AccuracyAccuracy

Definition: how close a measured value is to an accepted value

KEY POINT: accurate measurements = meaningful

Accurate

Not Accurate

PrecisionPrecision

Definition: how close a series of measurements are to one another

Key Point: more precision = more support if accurate

Precise

Not Precise

Accuracy vs. PrecisionAccuracy vs. Precision Accuracy: measurement vs. actual value Precision: similarity between repeated

measurements YOU CAN BE ACCURATE, PRECISE, BOTH OR

NEITHER!

Accurate

Precise, not accurate

Accurate AND Precise

Not Accurate, Not Precise

ErrorError

Error is a measurement of accuracyHigher error = less accurate measurement

(BAD!!)Equation:

error = |experimental – actual|

Example:Example:Julio weighed himself at the gym. The scale said he weighed 79.3 kg, but he really weighs 81.6 kg. What is the error in his measurement?

error = |experimental – actual| = |79.3 – 81.6|

= |-2.3| = 2.3 kg

Example as a Class!Example as a Class!

Christian measured the length of his Snickers bar to be 10 cm long. In reality, the candy bar is actually 9.5 cm long. What is the error in his measurement??

Error = |experimental – actual|

= |10 cm – 9.5 cm|

= |-0.5 cm|

0.5 cm!

BRING A CALCULATOR TOMORROW!

Classwork AssignmentSelect TWO of the following problems and calculate the error

in the following measurements on a separate sheet of paper. Turn into the homework stack when finished. Don’t foget units in your answers!

1. Experimental measurement: 4.5 km, Actual measurement: 3.2 km

2. Experimental measurement: 12.5 L, Actual measurement: 11.4 L

3. Sandra measured the mass of a ball to be 55.0 g, but the ball is really 53.9 g.

4. Juan thought the field looked about 122.5 m, but it was actually 135.9 m long.

5. Maria thought the glass held 344 mL of liquid, but it only had 315 mL.