Chapter 1 An Introduction to Physics - St. Monica Academy€¦ · Copyright © 2010 Pearson...

Copyright © 2010 Pearson Education, Inc.

Chapter 1 An Introduction to Physics


The Science of Physics

v Physics Is Everywhere! v Motion v Heat v Sound v Light v Electricity


What Is Physics All About? •  Matter •  Energy •  Force

“Stuff”


1-1 Physics and the Laws of Nature

Physics is the study of the fundamental laws of nature.

•  These laws can be expressed as mathematical equations.


Units of Measurement

v Le Système International d’Unités v SI

v Units Universally Used by Scientists



v SI Units v Length – meter (m) v Mass – kilogram (kg) v Time – second (s) v Temperature – Kelvin (K) v Amount – mole (mol)



v SI Units (Derived) v Area – square meter (m2) v Volume – cubic meter (m3) v Density – kilogram/cubic meter (kg/m3) v Energy – Joule kg*m2/s2 (J)


1-2 Units of Length, Mass, and Time SI units of length (L), mass (M), time (T): Length: the meter One meter is the distance traveled by light in a vacuum in 1/299,792,458 of a second Mass: the kilogram One kilogram is the mass of a particular platinum-iridium cylinder kept at the International Bureau of Weights and Standards, Sèvres, France. Time: the second One second is the time for radiation from a cesium-133 atom to complete 9,192,631,770 oscillation cycles.


1-4 Significant Figures

•  precision of measurements is limited

•  significant figures: the number of digits in a quantity that are known with certainty

•  Your Final Answer Cannot be More Accurate than Your Least Precise Entry.


Measurement: v Significant Figures (Rules)

v Zeros between other Nonzero digits ARE Significant EXAMPLE: 101.2

v Zeros in Front of Nonzero digits ARE NOT Significant EXAMPLE: 0.00004

v Zeros at the End of a Number, Right of the Decimal Point ARE Significant EX: 152.00

v Zeros at the End of a Number that doesn’t have a decimal point ARE Significant EX: 4000


1-4 Significant Figures •  the number of significant figures after multiplication or division is the number of significant figures in the least-known quantity Example: 10.75 * 3.54 = 38.1 •  the number of decimal places after addition or subtraction is the number of decimal places in the least-known quantity Example: 39864.25 + 3.4 = 39867.7 •  the number of significant figures in the value of

a trigonometric function is the number of significant digits in the angle

Example: sin 35.1° = 0.575


Measurement: v Significant Figures

v 1.024? v 0.0039? v 8.200m? v 600m? v 1.75m + 2.435m = v 3234.5m x 1.245m =

4 2 4 3

4.19m 4027m


Example: A tortoise travels at 2.51 cm/s for 12.23 s. How far does the tortoise go?

Answer: 2.51 cm/s × 12.23 s = 30.7 cm (three significant figures)



v Problem v 16.2m + 5.008m + 13.48m =


v Solution v 16.2m + 5.008m + 13.48m = 34.7m


v Problem v 5.006m + 12.0077m + 8.0084m =


v Solution v 5.006m + 12.0077m + 8.0084m = 25.022m


v Problem v 78.05cm2 – 32.046cm2 =


v Solution v 78.05cm2 – 32.046cm2 = 46.00cm2



Scientific Notation •  Leading or trailing zeroes can make it hard to determine number of significant figures: 2500, 0.00003602 •  Each of these has four significant figures •  Scientific notation writes these as a number from 1-10 multiplied by a power of 10, making the number of significant figures much clearer: 2500 = 2.500 × 103 Now write 0.00003602 in scientific notation: 0.00003602 = 3.602 x 10-5


1-5 Converting Units

Converting feet to meters:

1 m = 3.281 ft (this is a conversion factor)

Or: 1 = 1 m / 3.281 ft

316 ft × (1 m / 3.281 ft) = 96.3 m

Note that the units cancel properly – this is the key to using the conversion factor correctly!


v Problem: A bottle of wine contains 1.5L. How many mL does it contain? How many µL?


v Solution: 1.5L = 1.5x103 mL

1.5L = 1.5x106 µL


v Problem: A speed of 515.2 km/hr is the highest recorded train speed on any national rail system. Express this speed in meters per second.


v Solution:

515.2 km * 1000 m * 1 hr = 143.1 m/s hr km 3600 s


1-7 Scalars and Vectors

Scalar – a numerical value, usually positive. Examples: distance, speed, mass

Vector – a quantity with both magnitude and direction, may be positive or negative. Examples: displacement, velocity, force


1-8 Graphs v Graphs

v Variables v Independent Variable (IV)

v Manipulated by the Experimenter v Represented on the “x” axis v “Control” or “Explanatory” variable

v Dependent Variable (DV) v Variable(s) in the Experiment whose values

are dependent on the Independent Variable v Represented on the “y” axis v “Experimental” or “Response” variable


v Problem v A physics student placed a 1.0-kg mass on a

horizontal table that was nearly frictionless. The student then applied various horizontal forces to the mass and measured the acceleration for each force applied. The results of the experiment are shown in this table. Plot the values and draw the best fit curve.

Force (N) (m/s2) 5.0 4.9 10.0 9.8 15.0 15.2 20.0 20.1 25.0 25.0 30.0 29.9


v Solution ac

cele

ratio

n (m

/s2 )

Force (N)


v Problem v What is the relationship shown between force

and acceleration?

Force (N) (m/s2) 5.0 4.9 10.0 9.8 15.0 15.2 20.0 20.1 25.0 25.0 30.0 29.9

Force (N)

acce

lera

tion

(m/s

2 )

Direct (Linear) Variation


Homework

p. 16 Multiple Choice (all odd problems) pp. 17-19 Probs. 3, 9, 15, 21, 31, 35, 51, 55

Chapter 1 An Introduction to Physics - St. Monica Academy€¦ · Copyright © 2010 Pearson...

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