Notes:Color Guide • Gold: Important concept. Write this down. • Orange: Definition. Write this down. • Blue: Important information, but you do not need to copy. • Red: Example. Copy if needed. • White: Will be discussed by Ms. King.
Chapter 1: The Science of Physics Section 1: An Intro to Physics
Definition: physics – the study of the interactions between matter and energy. • Physics revolves around concepts that explain occurrences in the universe. • Examples: • Why does an object fall toward the ground instead of floating? • Why does a rolling ball stop after a while. • How do engineers know how much weight an elevator can hold?
Physics can be separated into many sub-branches: Mechanics Electromagnetism Nuclear Physics Aerodynamics Astrophysics Thermodynamics Optics Acoustics
? Obviously, physics involves the scientific method: Observing Hypothesizing Experimenting Drawing Conclusions • From the scientific method, theories, principles, and laws have been produced. • Definition: scientific theory - an explanation for an event that is based on observations only. • Definition: scientific law – a statement describing an event that always happens in the universe
Law vs. Theory • Theories are unproven…stuck at the “hypothesis” stage. • Scientific laws have been proven through repeated experimentation. Throughout the course, we will come across various laws. We will perform experiments to verify them.
Definition: data – a collection of recorded facts about an event. • Data is extremely important in physics. • Much of what we do will revolve around various types of data. • Some examples of data: • The speed of a train. • The mass of a rock. • The amount of time an object falls. • The amount of force applied to an object. • The angle at which a light ray reflects.
Most of our data will come in numerical form. • Much of this data will have “units” attached. • Definition: unit – a quantity used to measure data. • Measurements are meaningless without units. • Examples of units: • Cups • Liters • Pounds • Meters • Kilograms • Light Years • Feet • Inches m A kg s cd K mol
A m • Definition: base unit – a unit that cannot be broken down into other units. There are 7 base units. • Length/Distance: meter (m) • Mass: Kilogram (kg) • Time: second (s) • Temperature: Kelvin (K) • Electric Current: Amp (A) • Molecular Weight: Mole (mol) • Luminosity: candela (cd) We will define the rest of these units as we come across them. kg s cd mol K m kg s K A mol cd
Definition: derived unit – a unit produced by combining multiple base units. • Example: m/s (meters per second) is the unit for speed. • It is derived from two base units: meters & seconds. • Example: Newtons is the unit for force. • It is derived from kilograms, meters, and seconds. • We will encounter MANY derived units. • Understanding these units will help you understand how to rearrange formulas.
Prefixes can be used to modify the SI units. • Adding a prefix makes a unit larger or smaller. • For example: • One KILOmeter is equal to 1000 meters. • One millimeter equals .001 meters.
Accuracy vs Precision • When collecting data, it is important to realize that no measurement is perfect. • We describe the quality of data by its accuracy and precision. • Definition: accuracy – the quality of being close to the true value. • Accurate data is close to the actual value. • Definition: precision – the consistency of a measurement. • Precise data can be measured repeatedly to obtain the same value.
High Accuracy High Precision Accuracy vs Precision
Chapter 1: The Science of Physics Section 2: Representing Data
With a partner, answer the following: • What are two reasons for using graphs instead of numbers? • Describe what you see in each graph shown below.
Our focus, for now, will be on line graphs. However, there are several different “relationships” that can be seen on line graphs.
First, some stuff you need to understand. When experimenting, you will collect two types of data: Definition: independent variable – the factor that you change in an experiment. Definition: dependant variable – the factor that changes in response to the independent variable. Confused? How about an example…
Consider this: Carmen wants to determine if the amount of force an object hits the ground with changes when dropped from different heights. With your partner, discuss how Carmen should perform this experiment. Identify the dependent and independent variables, and explain why you chose them.
If you were to graph Carmen’s results, where would you place the data? Generally, the independent variable is placed on the X axis, and the dependent on the Y axis. Of course, there are always exceptions… Force Height
Suppose we plot several data points, shown on the graph. If we were to draw a “line” that best fits on top of those points, what kind of line would it be? A straight line, of course. Definition: best fit line – the line that can be drawn as close as possible to every data point on a graph.
In this case, the best fit is “linear”. • Definition: linear relationship – a scenario in which the best fit is a straight line. • It is represented by the equation y = mx+b. • “b” is the y-intercept…the point where the graph crosses the y-axis. • It’s also the value of y when x=0. • Slope is rise/run, or Δy/Δx. Sound familiar??
Drawing the best fit line does NOT mean that you connect the dots! Nor does it always start at the origin.