PHYSICS & MEASUREMENT

RESUME OF PHYSICS TASK

PHYSICS & MEASUREMENT

 

ANDI RYANSYAH (3415106799)

LUTHFI ANZANI (3415106770)

MECHANICS

Physics and Measurement

1.1 Standards of Length, Mass, and Time.

1.2 Matter and Model Building.

1.3 Density and Atomic Mass.

1.4 Dimensional Analysis.

1.5 Conversion of Units.

1.6 Estimates and Order-of-Magnitude

      Calculations.

1.7 Significant Figures.

1.1 Standards of Length, Mass, and Time.

In 1960, an international committee established a set of standards for the fundamental quantities of science. It is called the SI (Système International), and its units of length, mass, and time are the meter, kilogram, and second, respectively. Other SI standards established by the committee are those for temperature (the kelvin), electric current (theampere), luminous intensity (the candela), and the amount of substance (the mole).

 

LENGTH

As recently as 1960, the length of the meter was defined as the distance between two lines on a specific platinum–iridium bar stored under controlled conditions in France. This standard was abandoned for several reasons, a principal one being that the limited accuracy with which the separation between the lines on the bar can be determined does not meet the current requirements of science and technology. In the 1960s and 1970s, the meter was defined as 1 650 763.73 wavelengths of orange-red light emitted from a krypton-86 lamp. However, in October 1983, the meter (m) was redefined as the distance traveled by light in vacuum during a time of 1/299 792458 second.

MASS

The SI unit of mass, the kilogram (kg), is defined as the mass of a specific platinum–iridium alloy cylinder kept at the International Bureau of Weights and Measures at Sèvres, France. This mass standard was established in 1887 and has not been changed since that time because platinum–iridium is an unusually stable alloy. A duplicate of the Sèvres cylinder is kept at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland.

TIME

In 1967, the second was redefined to take advantage of the high precision attainablein a device known as an atomic clock (Fig. 1.1b), which uses the characteristic frequencyof the cesium-133 atom as the “reference clock.” The second (s) is now defined as 9 192 631770 times the period of vibration of radiation from the cesium atom.

                                                                                                           

          

            (a)                                                                         (b)

Figure 1.1 (a) The National Standard Kilogram No. 20, an accurate copy of the

International Standard Kilogram kept at Sèvres, France, is housed under a double bell jar in a vault at the National Institute of Standards and Technology. (b) The nation’s primary time standard is a cesium fountain atomic clock developed at the National Institute of Standards

and Technology laboratories in Boulder, Colorado. The clock will neither gain nor lose a second in 20 million years.\

1.2 MATTER and MODEL BUILDING

Quark have 6 different varieties:

1. up(+2/3)

2.charmed(+2/3)

3.top(+2/3)

4.down(-1/3)

5.strange(-1/3)

6.Bottom(-1/3)

a.Proton=2 up+1down=2(+1/3)+(-1/3)=+1

b.Neutron=1up+2down=+1/3+2(-1/3)=0

                                                           

                                                                                                                                                                                                                                                              

 RUTHERFORD ATOM MODEL                                                      THOMPSON ATOM MODEL

1.3 Density&atomic mass

Density p of any substance is defined as its mass per unit volume:

P=m/v

The numbers of protons and neutrons in the nucleus of an atom of an element are related to the atomic mass of the element, which is defined as the mass of a single atom of the element measured in atomic mass unit. Atomic Mass = proton+neutron

*Quick quiz  1.1

In a machine shop, two cams are produced, one of aluminum and one of iron. Both cams have the same mass. Which cam is larger?

(a) The aluminum cam

(b) the iron cam

(c) Both cams have the same size.

ANSWER: (a). Because the density of aluminum is smaller than that of iron, a larger volume of aluminum is required for a given mass than iron.

1.4 Dimensional Analysis

For example, the symbol we use for speed in this book is v, and in our notation the dimensions of speed are written [v]=L/T. As another example, the dimensions of area A are [A]=L²

*Quick quiz 1.2

True or False: Dimensional analysis can give you the numerical value of constants of proportionality that may appear in an algebraic expression.

ANSWER: False. Dimensional analysis gives the units of the proportionality constant but provides no information about its numerical value. To determine its numerical value requires either experimental data or geometrical reasoning.

1.5 Conversion of Units.

Sometimes it is necessary to convert units from one measurement system to another, or to convert within a system, for example, from kilometers to meters. Equalities between SI and U.S. customary units of length are as follows:

1 mile = 1 609 m = 1.609 km            1 ft = 0.304 8 m = 30.48 cm

1 m = 39.37 in. = 3.281 ft                  1 in. = 0.025 4 m = 2.54 cm (exactly)

*Quick Quiz 1.3

The distance between two cities is 100 mi. The number of kilometers between the two cities is

(a)  smaller than 100

(b)  larger than 100

(c)  equal to 100.

ANSWER: (b). Because kilometers are shorter than miles, a larger number of kilometers is required for a given distance than miles.

1.6 Estimates and Order-of Magnitude Calculations

It is often useful to compute an approximate answer to a given physical problem even when little information is available. This answer can then be used to determine whether or not a more precise calculation is necessary.

Such an approximation is usually based on certain assumptions, which must be modified if greater precision is needed. We will sometimes refer to an order of magnitude of a certain quantity as the power of ten of the number that describes that quantity. Usually, when an order-of magnitude calculation is made, the results are reliable to within about a factor of 10. If a quantity increases in value by three orders of magnitude, this means that its value increases by a factor of about 10³ = 1 000. We use the symbol ~ for “is on the order of.”

Thus, 0.008 6 ~ 10^-2       0.002 1 ~ 10^-3     720 ~ 10³

1.7 Significant Figures

The number of significant figures in a measurement can be used to express something about the uncertainty. For example, if we wish to compute 123 + 5.35, the answer is 128 and not 128.35. If we compute the sum 1.000 1 + 0.000 3 = 1.000 4, the result has five significant figures, even though one of the terms in the sum, 0.000 3, has only one significant figure. Likewise, if we perform the subtraction 1.002 - 0.998 = 0.004, the result has only one significant figure even though one term has four significant figures and the other has three. In this book, most of the numerical examples and end-of-chapter problems will yield answers having three significant figures. When carrying out estimates we shall typically work with a single significant figure.

*Quick Quiz 1.4

Suppose you measure the position of a chair with a meter stick and record that the center of the seat is 1.043 860 564 2 m from a wall. What would a reader conclude from this recorded measurement?

ANSWER : Reporting all these digits implies you have determined the location of the center of the chair’s seat to the nearest *0.000 000 000 1 m. This roughly corresponds to being able to count the atoms in your meter stick because each of them is about that size! It would be better to record the measurement as 1.044 m: this indicates that you know the position to the nearest millimeter, assuming the meter stick has millimeter markings on its scale.