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What is Physics?

The goal of physics is to use a small number of basic concepts , equations , and assumptions to describe the physical world. These physics principles can then be used to make predictions about a broad range of phenomena.

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What is Physics?

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  1. The goal of physicsis to use a small number of basic concepts, equations, and assumptions to describe the physical world. • These physics principles can then be used to make predictionsabout a broad range of phenomena. • Physics discoveries often turn out to have unexpected practical applications, and advances in technology can in turn lead to new physics discoveries. What is Physics?

  2. There is no single procedure that scientists follow in their work. However, there are certain steps common to all good scientific investigations. • These steps are called the scientific method. The Scientific Method

  3. A hypothesis must be tested in a controlled experiment. A controlled experiment tests only one factor at a time by using a comparison of a control groupwith an experimental group. Controlled Experiments

  4. SI Standards

  5. In SI, units are combined with prefixesthat symbolize certain powersof 10. The most common prefixes and their symbols are shown in the table. SI Prefixes

  6. Measurements of physical quantities must be expressed in units that match the dimensions of that quantity. • In addition to having the correct dimension, measurements used in calculations should also have the same units. Dimensions and Units For example, when determining area by multiplying length and width, be sure the measurements are expressed in the same units.

  7. Accuracy is a description of how close a measurement is to the correct or accepted value of the quantity measured. • Precision is the degree of exactness of a measurement. • A numeric measure of confidence in a measurement or result is known as uncertainty. A lower uncertainty indicates greater confidence. Accuracy and Precision

  8. It is important to record the precision of your measurementsso that other people can understand and interpret your results. • A common convention used in science to indicate precision is known as significant figures. • Significant figuresare those digits in a measurement that are known with certainty plus the first digit that is uncertain. Significant Figures

  9. Even though this ruler is marked in only centimeters and half-centimeters, if you estimate, you can use it to report measurements to a precision of a millimeter.

  10. Rules for Determining Significant Zeros

  11. Rules for Calculating with Significant Figures

  12. Tables, graphs, and equations can make data easier to understand. Mathematics and Physics

  13. quantitative graph - shows the relationship between two variables in the form of a curve For the relationship: y =f (x) x- the independent variable • plotted along horizontal axis • positive values to the right of the origin • is the one over which the experimenter has complete control y- the dependent variable • plotted along vertical axis • positive values above the origin • the one that responds to changes in the independent variable Graphical Methods

  14. Ex: In an experiment where given amount of gas expands when heated at a constant pressure, the relationship between the variables, V and T, may be graphically represented as follows It is proper to plot V= f(T) rather than T= f(V) The experimenter can control the temperature of the gas, but the volume can only be changed by changing the temperature

  15. The process of matching an equation to a curve is called curve fitting. • The desired empirical formula, can usually be determined by inspection, and requires an assumption that the curve represents a linear or simple power function. • If data plotted on rectangular coordinates yields a straight line, the function y= f(x) is said to be linearand the line on the graph could be represented algebraically by the slope-intercept form: y = mx+b where: m -is the slope b –is y-intercept Curve Fitting

  16. Consider the graph of • velocity vs. time • The curve is a straight line, indicating that v =f(t) is a linear relationship v =mt +b where slope m =(Δv) / (Δt)= (v2-v1) /(t2-t1) from the graph m = (8.0m/s)/(10.0s)= 0.80 m/s2 • The curve intercepts the v-axix at v =2.0 m/s ( velocity when the first measurement was taken) when t =0, b =v0 =2.0m/s • The general equation, v =mt +b can be rewritten as v =(0.8 m/s2)t + 2.0m/s

  17. Consider the graph of Pressure vs. Volume: • The curve appears to be a hyperbola (inverse function). This function suggest a test plot of P vs 1/V. • The equation for this straight line is: P= m(1/V) +b where b =0, P =m(1/V) when rearranged, this yields PV = constant which is known as Boyle’s Law

  18. Consider the graph of distance vs. time. • The curve appears to be a top-opening parabola • This function suggest that a test plot be made of d vs. t2 • Since the plot is linear • d =mt2+b • The slope m =(Δd) / (Δt2) =(.80m)/(.50s)2= 1.6m/s2 b=0 (curve passes through the origin) The mathematical expression that describes the motion of the object is: d =(1.6m/s2)t2

  19. Consider the graph of distance vs. height • The curve appears to be a side-opening parabola. This function suggest a plot be made of d2 vs. h • Since the graph is linear, the expression is:d2= mh +b • The slope m =Δd2 / Δh m =2.5 cm2/ 5.0 cm= 0.50cm • b=0 (the curve passes through origin) • The mathematical expression is: d2 = (0.5 cm)h

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