Chapter 1: The Nature and Science of Physics Textbook Notes

• Physics


  Branch of science that describes the interactions of energy, matter, space, and time; and the fundamental mechanisms that underlie every phenomenon
• Model


  A representation of something that is often too difficult to display directly. While it is justified with experiments, it is accurate under limited situations.
• Theory


  An explanation for patterns in nature that is supported by scientific evidence and verified multiple times by various groups of researchers. Some include models.
• Law


  Uses concise language to describe a generalized pattern in nature that is supported by scientific evidence and repeated experiments. It can often be expressed in the form of a mathematical equation
• Scientific method


  The process of how scientists inquire and gather information about the world. It begins with an observation and question the scientist will research. Then, the scientist performs some research and forms a hypothesis. Next, they will test that hypothesis through an experiment. Last, the results are analyzed and the scientist draws a conclusion.
• Classical physics


  Physics as it was developed from the Renaissance to the end of the 19th century. It gave approximations under the conditions that matter must be moving at speeds less than 1 percent of the speed of light, objects dealt with must be large enough to be seen with a microscope, and only weak gravitational fields can be involved.
• Modern physics


  Consists of relativity and quantum mechanics, which deal with the very fast and the very small.
• Relativity


  Must be used whenever an object is traveling at greater than about 1 percent of the speed of light or experience a strong gravitational field
• Quantum mechanics


  Must be used for objects smaller than what can be seen with a microscope
• Relativistic quantum mechanics


  Describes the behavior of small objects traveling at high speeds or experiencing a strong gravitational field. It is the best universally applicable theory we currently have.
• Physical quantity


  Defined by specifying how it is measured or by stating how it is calculated from other measurements
• Units


  Standardized values that express measurements of physical quantities
• English units, customary, or the imperial system


  Units historically used in nations once ruled by the British empire and still widely used in the US.
• SI units or the metric system


  The units used by nearly every country other than the US. It is also the system used by mathematicians and scientists.
• Fundamental units


  The units that are used to measure fundamental physical quantities. Includes length (in meters), mass (in kilograms), time (in seconds) and electrical current (in ampere)
• Derived units


  The units for all physical quantities other than the fundamental physical quantities. They can be expressed as algebraic combinations of length, mass, time, and electrical current
• Second or s

  The time required for 9,192,613,770 Cesium atoms vibrations to occur.
• Meter or m


  The distance light travels in a vacuum in 1/299,792,458 of a second
• Kilogram or kg


  Defined in terms of the second, meter, and Planck's constant (h)
• Order of magnitude


  The scale of a value expressed in the metric system.
• Conversion factor


  A ratio expressing how many of one unit are equal to another unit. Ex: 12 inches in 1 foot.
• Suppose you drive the 10.0 km from school to home in 20.0 min. Calculate the average speed (a) in kilometers per hour and (b) in meters per second.

  (a) 60 min/hr (b) 8.33 m/s
• Some hummingbirds beat their wings more than 50 times per second. A scientist is measuring the time it takes for a hummingbird to beat its wings once. Which fundamental unit should the scientist use to describe the measurement? Which factor of 10 is the scientist likely to use to describe the motion precisely? Identify the metric prefix that corresponds to this factor of 10.

  They will use the fundamental unit of seconds. They will likely need to measure in milliseconds, or 10^-3 seconds.
• Accuracy


  How close a measurement is to the correct value for that measurement
• Precision


  How close the agreement is between repeated measurements, which are repeated under the same conditions
• Uncertainty


  A quantitative measure of how much your measured values deviate from a standard or expected value. If measurements are not accurate or precise, this measure will be high.
• Factors contributing to uncertainty

  Limitations of the measuring device, the skill of the person making the measurement, irregularities in the object being measured, and any other factors that affect the outcome.
• Percent uncertainty

  Delta A / A X 100%
• A grocery store sells 5 pound bags of apples. You purchase four bags over the course of a month and weigh the apples each time. You obtain the following measurements: week 1: 4.8 lb, week 2: 5.3 lb, week 3: 4.9 lb, and week 4: 5.4 lb. You determine that the weight of the 5 lb pound has an uncertainty of +/- 0.4lb. What is the percent uncertainty of the bag's weight?

  5lb +/- 8%
• Method of adding percents


  The percent uncertainty in a quantity calculated by multiplication or division is the sum of the percent uncertainties in the items used to make the calculations.
• A high school track coach has just purchased a new stopwatch. The stopwatch manual states that the stopwatch has an uncertainty of +/- 0.05s. The team's top sprinter clocked a 100 meter sprint at 12.04 seconds last week and at 11.96 seconds this week. Can we conclude that this week's time was faster.

  No, the uncertainty of the stopwatch is too great to effectively differentiate.
• Determine the number of significant figures in the following measurements: A). 0.0009, b) 15,450.0, c) 6 X 10^3, d) 87.990, and e) 30.42

  a.) 1, b) 6, c) 1, d) 5, and e) 4
• A woman has two bags weighing 13.5 pounds and one with a weight of 10.2 pounds. What is the total weight of the bags with correct significant figures?

  37.2 pounds
• The force, F, on an object is equal to its mass, m, multiplied by its acceleration, a. If a wagon with mass 55 kg accelerates at a rate of 0.0255 m/s^2, what is the force of the wagon?

  1.4 N
• Approximate the height of a 39-story building if 2 people make up one story and 1 person is 2m.

  156m