Calculators - Sept 15 Class

- Your calculator has functions that you can use to do this easily

• EXP
• EE
• X10
• S.N.

- Do NOT use the '^' on your calculator. It does not recognize the order of operations in all cases

Expressing Error
- Error is a fundamental part of science
- There are usually 3 reasons for error:

Physical errors in the measuring device

'Sloppy' measuring

Changing ambient conditions

- Error is taken to be half the smallest division on your measuring device

Calculated Errors
- Two different parts of possibilities: Absolute Error and Percentage Error
- Absolute Error:

• measured value minus accepted valueabsolute error = measured - accepted
• positive number means you're over the accepted value
• negative number means you're under the accepted value

- Percentage Error:

• most common
• percent error = absolute error/accepted value
  

Example: You measured the weight of an orange to be 15N. The atual weight is 17.5 N. What i the percentage error? (14%)

Dimensional Analysis

- Want to know what 100km/h is in miles/hour?
- Just like converting between currencies, in Chemistry it is usually necessary to convert between units.. this process is called dimensional analysis

Steps
- There are 4 steps:

1. Find a unit equality
2. Find the conversion factors
3. Add a conversion factor
4. Cancel units

Example: How many miles are equal to 120 km?

Posted by Erin

Measurement & Chemistry - Sept 11 Class

In friday's lesson we learned the 7 Fundamental Units, Prefixes & SI units, and Significant Digits.

- Accurate measurements are essential in the scientific method.
- The SI system (System International) is the most common system in use today.
- France started the metric system about 300 years ago.

7 Fundamental Units (*need to know or most likely to use)

• Mass* (kg)
• Distance* (m)
• Time* (s)
  
• Temperature* (K)
  
• Amount* (mol) ----> 6.02 x 10^23
  
• Current (A)
  
• Luminosity (cd)

Prefixes & SI Units

Use the prefixes to convert the symbols!


Significant Digits
1. Digits 1-9 are always significant.
2. Zeros are significant if they are right of the decimal.

EX. 2.010-->ALL 4 digits are significant compared to 0.002-->ONLY the "2" is significant.