Physics Chapter 1

1. Physics Chapter 1

2. What is Physics? • The study of the physical world with the use of basic concepts, equations and assumptions to describe the physical world

3. Any problem that deals with temperature, size, motion, position, shape or color involves physics

4. The Scientific Method • No single set of procedures that scientists follow but there are certain steps common to all good investigations

6. Models • Physicists often use them to explain the most fundamental features of various phenomena • Because it is usually impossible to describe all aspects of the phenomenon at the same time • To analyze an event or observation • They break it down into parts and then decide which parts are impossible to study

8. Models • Ex. Basketball – many observations can be made about the game: size, spin, weight, etc. – simplify and decide what to study • System  a set of items or interactions considered a distinct physical entity for the purpose of study – then eliminate all other information • Say you want the system to be (time in the air), eliminate factors that don’t affect this system

9. Models • They help build hypotheses • Galileo – scientists at the time thought heavier objects fell faster than lighter objects. Galileo hypothesized that all objects fell at the same rate in the absence of air resistance • He performed many experiments keeping all variables the same except for the weight • Controlled experiment – experiment involving manipulation of a single variable or factor • Conclusions must be able to be verified by others because scientists also research the work of other scientists

11. Measurements in Science • To test a hypothesis about how changing one variable affects another variable – measurements must be made and the number can’t stand alone – we use units to express what is being measured – dimension • Basic dimensions – length, mass, time, temperature and electric current

12. Standard Measurement for Science • SI or Systeme International – with 7 base units each describing a single dimension • Length – meter – m • Mass – kilogram – kg • Second – time – s

14. Units can be combined, depending on what is observed – derived units are formed by combining the 7 base units with multiplication or division – m/s for speed • Newtons (N) = 1 kg * m/s2

16. Physics describes a broad range of topics and requires measurements from very small to very large between them. Because they are hard to read and write, they are expressed in powers of 10

18. Accuracy and Precision • Careful measurements are crucial to physics because theories are based on observation and experimentation • Accuracy – describes how close a measured value is to the true value of the quantity measured • Precision – refers to the degree of exactness with which a measurement is made and stated

20. Accuracy vs. Precision • Ex. Shoe for measurement exp. • The shoes measurement has little accuracy – how do you estimate a fractional part of the shoe • The tool (shoe) lacks precision because repeated measurements produce little agreement

21. Problems with accuracy are due to error • Human error occurs so take repeated measurements to be certain they are consistent or accurate • Method error occurs if different ways to obtaining a measurement is done • When measuring length with a meter stick, choose a line of sight directly over what is being measured • Ex. Parallax – speedometer more accurately read by driver. Why? • Instrument error – calibrate all lab equipment before use

23. Precision describes the limitations of the measuring instrumentPrecisPrecision describes the limitations of the measuring instrumention describes the limitations of the measuring instrument • Precision describes the limitations of the measuring instrument • A measurement of 1.325 m more precise than 1.3 m • Such as trying to measure millimeter with a ruler marked only in centimeters you might have to estimate

25. Significant figures • Significant figures – digits in a measurement that are known with certainty plus the first digit that is uncertain • Pencil measurement – 18 cm was actually measured with the ruler and the 3rd significant figure is the estimated number • When using 0’s it is difficult to tell whether it is a place holder or a significant digit • To correct this problem report all values using scientific notation

28. Rules for calculating with significant figures • + or – : final answer should have the same number of digits to the right of the decimal as the smallest measurement with the smallest number of digits to the right of the decimal • * or / : final answer has the same number of significant figures as the measurement having the smallest number of significant figures

29. Calculators are great but they often exaggerate the precision of your final results – in order to provide answers with the correct number of significant figures – you will have to round the results of a calculation

30. Mathematics and Physics • Tables, graphs and equations make data easier to understand • Graphs – to better analyze data – look for patterns or trends • They summarize date from tables and/or indicate relationships between variables • Equations – show how 2 or more variables are thought to be related • Many physics equations do not contain numbers because they represent a simple description of the relationship between physical quantities • Letters are used to represent specific quantities – variables and other specific quantities are abbreviated with letters that are bold or italicized • Units are simply abbreviated

31. Evaluating Physics Expressions • Dimensional analysis can weed out invalid equations • Quantities can be added or subtracted only if they have the same dimensions and the 2 sides of an equation must have the same dimensions • Order of magnitude estimations check answers • Determining the power of 10 that is closest to the actual numerical value of the quantity • Can be used to estimate numbers in situations in which little info is given