The Physics of Everyday Things
What is Physics?
Physics is the branch of science that deals with the properties and interactions of matter and energy. First we start off with Conversions and Measurement.
Conversions and Measurement
SI System - the internationally accepted system of measurement
The SI System contains seven base units, to all of which prefixes can be added to group the units as larger or smaller
Q: Convert 1.08 kg to mg.
Find your current prefix on the chart and the one you are converting to. One kilograms is 106 times larger than one milligram, so you would move the decimal place over six places to the left.
A: 1,080,000 mg
Lab Summary - SI System
The lab about the SI System demonstrated why it is important that everyone use the same units. Using the SI System makes it easier for people to work together, leaving less room for error when making difficult conversions from other units of measurement. In this lab, we built boxes of paper using our fingers to measure and all the boxes turned out to be slightly different sizes, which would not be the case were a standard unit of measurement used.
Significant Figures
Significant figures allow your measurements to be accurate
All numbers are significant except:
- All zeroes to the right of a decimal but to the left of a non-zero ex. 0.00045 (2 sig figs)
- Zeroes placed at the end of a number with no decimal unless stated ex. 604,000 (3 sig figs)
- The customary zero placed at the before a decimal ex. 0.663947 (6 sig figs)
When multiplying or dividing, you must have the same number of significant figures as the number with the least amount of significant figures within the question
When adding or subtracting, round all numbers to the same amount of decimal places before performing the operation and you must have the same units
Lab Summary - Uncertainty in Measurement
This lab helped us to see the difference between precision and accuracy and their importance in physics and measurement. Precision is about how small of a unit you are able to measure to. Accuracy is how correct your measuring is. Here we learned about percent error, which show you how large or small your error in measuring is compared to the accepted values. Absolute deviation was another concept, which compares the observed value to an average of a set of values. In summary, this lab focused on the importance of correct measurement and significant figures in reporting errors.
Formulas
Percentage Error = Observed Value - Accepted Value x100%
Accepted Value
Absolute Deviation = (Observed Value – Average Value)
Scientific Notation
Scientific notation is used to represent very large or very small numbers.
- When multiplying numbers in scientific notation, add the exponents.- When dividing, subtract the exponents.
- When adding or subtracting, the exponents must be the same and then you may add or subtract the significant digits as they are.
Ratios
Ratios are can be helpful when making conversions.
Constructing and Interpreting Data
When making a graph:- On the x-axis should be the independent variable- On the y-axis should be the dependent variable (the data that is measured)- Label properly with units and a title “Y vs. X”- Draw a line of best fit- Find the equation of your line by choosing two points on your line, finding the slope (m) and using the y = mx+b formula
Interpolation - when you read information from your graph from within the data that you graphed
Extrapolation - when you read info from your graph from outside the data you graphed
Direct relationship - when one variable increases the other variable increases
Inverse relationship - when one variable increases the other variable decreases
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