Notes

Outline

Physics 2001 Introduction: What is Physics The scientific study of the basic properties of matter and energy

The Galaxies, The Large View

The Cosmos

The Atom- The small view

The small-Fundamental Particles

Science An organized method of study using the scientific method: Observation Hypothesis Experiment Modification of Hypothesis

Parts of Science Consists of Physical Sciences, Life Sciences, Social Sciences

Physical, Social and Life Sciences Life Sciences Biology, Anatomy,Physiology,… Physical Sciences Physics, Geology, Chemistry,… Social Sciences: Psychology, Sociology..

Physics 2001 Chapter 1 Motion

Drag Racing-an example of the importance of acceleration and average speed In drag racing the first car to the end of the course wins. This usually means the one with the fastest acceleration However one car can accelerate faster at the beginning and the other might still win if it accelerates more at the end.

3 Basic Aspects of Nature Space Time Matter

3 Fundamental Physical Quantities Distance Time Mass

Units Size or amount used in measuring something (physical quantity) Based on standard, Standard: something of known size, e.g. Length of Kings Foot = “Ruler”, or foot.

Aspect vs Quantity Space vs Distance…Distance=how space is measured feet, meters, miles, etc. Time vs. Time in seconds, min.,etc Matter vs mass, mass=how matter is measured kilogram, gram, slug, etc.

Exponents An exponent is a number telling us the other number is multiplied by itself this many time. 102 = 10 x 10 =100 104 = 10 x 10 x 10 x 10 Negative exponents are 1 divided by the number 10-2 = 1/10 x 1/10  or .01 (2 decimal places) 10-4 = 1/(10 x 10 x 10 x 10) = .0001 (4 dec. places)

Prefixes A word put in front of another word to alter the meaning of the word. Example word: boat, Prefix: life New word: lifeboat In physics we use prefixes frequently, especially in units.

Metric System A special system of units, consisting of units for all the known physical quantities and concepts used by science. Example length: meter Mass: Gram Time: second Prefix: kilo = 1 thousand, kilometer = 1000 meters; kilogram = 1000 grams.

Common Prefixes in the Metric System Deci = 1/10th Deca = 10 times Centi = 1/100th  = 10 -2 Milli = 1/1000th =  10 -3 Micro = 1/1000,000th  = 10 -6 Mega = 1,000,000 times  =   10 +6 Giga = 1,000,000,000 times  = 10 +9

Physical Objects

Measurement

Length, Time

The Breath Experiment

Metric vs. British System

Conversions To convert from one unit to another Get the conversion factor Multiply it by the number of units E.g. 1 m = 3.28 ft 12 m = 12 x 3.28 = 39.36 ft

Cycle and Period: A cycle is one complete phase of  something Period (T) The time for one complete cycle of a periodic process.

Frequency (f) The number of cycles of a periodic process that occur per unit time. The unit of measure of frequency is the hertz (Hz). (s-1 =1/sec) To get frequency from period, divide 1 by period.  T=12(s), f = 1/12(Hz)

Mass (m) . A measure of an object's resistance to acceleration. A measure of the quantity of matter in an object Measured in grams, kg (SI units), slugs (British Units)

Speed (v) Rate of movement. Rate of change of distance from a reference point. The distance that something travels divided by the time elapsed. V= Δd/Δt  (Δ = greek letter delta, = change in something). Δd/Δt = change in distance/change in time (time for the change to happen)

Calculating Speed An object is 8 ft from the door, 3 seconds later it is 23 feet from the door, Δd=final-original=23-8=15 ft The object moves 15 feet in 3 seconds V= Δd/Δt = 15/3 = 5 ft/sec

Velocity Velocity is Speed with direction. E.G. 90 meters/second North 30 meters/second South West 80 mph South, etc.

Vectors vs Scalars Vectors have size and direction, e.g. 90 meters North Scalars have only size, e.g. 90 meters. Vector 120 miles per hour (mph) East (E). Scalar 120 miles per hour We draw vectors on paper to represent them.

Drawing Vectors When representing a vector we must use a grid, the grid shows direction, like North, South, East, and West, and size. For example the size of 1 inch on the grid may stand for 10 miles per hour of velocity.  This is the “scale” Something 2 inches long would be 20 miles per hour.

One Dimensional Vector Addition Back and forth in the same direction.

Two Dimensional Vector Addition, To add vectors: Draw the first vector, A Draw the second vector,B, with it’s tail starting at the head of the first vector The answer, or resultant is drawn from the tail of the first to the head of the last.

Vector Addition Example

Average Speed Vs Instantaneous Speed, Velocity, Average speed is speed over some time or distance, but it may be changing, to know it exactly we need to know it at a very short “instant” in time.  This is the instantaneous speed or velocity.

Trigonometry,

Pythagorean Theorem, Right Triangles,  c2 = a2 + b2 Hypotenuse squared = sum of the squares of the sides in a right triangle

Pythagorean Theorem

30 deg. triangle

3-4-5 Right Triangle 3-4-5 Right Triangle

Acceleration Rate of change of velocity. The change in velocity divided by the time elapsed. Δv/Δt = change in velocity/change in time (time for the change to happen)

Example of Acceleration Problem Velocity 9 m/s E After 2 sec. v= 15 m/s E Change in v=(final-original)15-9 or 6 m/s E  a=Δv/Δt a = 6m/s/2sec = 3 m/s/s(m/s2) E

Determining v from a and t When a is constant, v = a x t  a = 5 m/s2  t = 20 s  v = 5 m/s2 x 20 s = 100 m/s

Centripetal Acceleration Acceleration of an object moving along a circular path. It is directed toward the center of the circle. a = v2/r = square of velocity divided by the radius of the circle.

Example Cent. Acc. Particle moves in a circle of radius 5 m Speed is 12 m/s.  What is Cent. Acc.? Cent. Acc. = v2/r = (12 m/s)2 / 5 m = 144 m2/s2 / 5m = 28.8 m/s2

Simple Types of Motion: Zero Velocity, Constant Velocity  d = v x t  when v=constant E.g. v = 10 m/s; t = 5 s  d = 10 m/s x 5 s = 50 m

Distance vs. Time Graphs, Slope of the distance vs time graph = velocity

Constant Speed Graphs Speed vs. time, plots a straight line.

Accelerated motion, When velocity is changing we have accelerated motion. The simplest case is when acceleration is constant, such as the acceleration of gravity near the earth’s surface.

Speed vs. Time Graphs. When speed is constant the graph is a straight horizontal line. When speed is accelerated uniformly (constant acceleration) the graph is a straight line at an angle. The slope is the acceleration. See fig. 1.26

Constant Acceleration, Acceleration of Gravity  g = acceleration of gravity = 9.8 m/sec/sec. d = ½ at2  (½ x a x t x t)

D = ½ at2 Problem  a = 9.8 m/s2  t = 5 sec.  What is d? ½ at2 = ½ x 9.8 m/s2 x 5 s x 5 s = 4.9 x 25 m /s2 x s2 = 122.5 m

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