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DESCRIBING BASICS OF VECTORS IN DETAILED
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physics oscillations and waves
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11TH GRADE PHYSICS
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PHYSICS FOR GRADE 11
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PHYSICS- GRADE 11 AND GRADE 12 (MODE1)UNIT 1 Measurement
Learning Objectives
1.01 Identify the base quantities in the SI system.
1.02 Name the most frequently used prefixes for SI units.
1.03 Change units (length, area, and volume) by using chain-link conversions
1.04 Explain that the meter is defined in terms of the speed of light in vacuum
1.What Is Physics?
Physics is based on measurement of physical quantities. Certain physical quantities have been chosen as
base quantities (such as length, time, and mass); each has been defined in terms of a standard and given
a unit of measure (such as meter, second, and kilogram). Other physical quantities are defined in terms
of the base quantities and their standards and units.
Physics is the branch of science deals with design and conduct the experiments.
EXAMPLE: Without clocks of extreme accuracy, the Global Positioning System (GPS) that is now vital to
worldwide navigation would be useless.;
2.Measuring Things:
We measure each physical quantity in its own units, by comparison with a standard. The unit is a unique
name we assign to measures of that quantity
EXAMPLE: meter (m) for the quantity length
Base Quantities: A small number of physical quantities, such as length and time, and assign standards to
them alone. We then define all other physical quantities in terms of these base quantities and their
standards.
Quantity Unit Name Unit Symbol
Length meter m
Time second s
Mass kilogram kg
3) Changing Units
We often need to change the units in which a physical quantity is expressed. We do so by a method
called chain-link conversion. In this method, we multiply the original measurement by a conversion
factor (a ratio of units that is equal to unity). For example, because 1 min and 60 s are identical time
intervals, we have
,1 min/60sec= 1 and 60 s/1 min=1
Thus, the ratios (1 min)/ (60 s) and (60 s)/ (1 min) can be used as conversion factors. This is not the same
as writing 1/60 =1 or 60 = 1must be treated together.
Because multiplying any quantity by unity leaves the quantity unchanged, we can introduce conversion
factors wherever we find them useful. In chain-link conversion, we use the factors to cancel unwanted
units. For example, to convert 2 min to seconds, we have
2 min = (2 min) (1),2min{60min/1min} =120sec
If you introduce a conversion factor in such a way that unwanted units do not cancel, invert the factor
and try again. In conversions, the units obey the same algebraic rules as variables and numbers.
4.Length
The meter came to be defined as the distance between two fine lines engraved near the ends of a
points, object, mediums.
The meter is the length of the path traveled by light in a vacuum during a time interval of 1/299 792 458
of a second. This time interval was chosen so that the speed of light c is exactly c =299 792 458 m/s.
Observation
Sample Problem 1.01 Estimating order of magnitude, ball of string
The world’s largest ball of string is about 2 m in radius. To the nearest order of magnitude, what is the
total length L of the string in the ball?
Analysis
We could, of course, take the ball apart and measure the total length L, but that would take great effort
and make the ball’s builder unhappiest. Instead, because we want only the nearest order of magnitude,
we can estimate any quantities required in the calculation.
Calculations: Let us assume the ball is spherical with radius R= 2 m. The string in the ball is not closely
packed (there are uncountable gaps between adjacent sections of string). To allow for these gaps, let us
somewhat overestimate the cross-sectional area of the string by assuming the cross section is square,
with an edge length d =4 mm. Then, with a cross-sectional area of d² and a length L, the string occupies a
total volume of
V= (cross-sectional area) *(length)=d²L
This is approximately equal to the volume of the ball
4 3
Given, π r which is about 4 R3 because π is about 3. Thus, we have the following
3
2 3
ⅆ L=4 R
3
4R
L= 3
2 =4*2 m /(4*10
−3
) which is 2∗106 m 106=103 km
d
,5)Time
Time has two aspects. For civil and some scientific purposes, we want to know the time of day so that
we can order events in sequence. In much scientific work, we want to know how long an event lasts.
Thus, any time standard must be able to answer two questions: “When did it happen?” and “What is its
duration?”
Definition: -Any phenomenon that repeats itself is a possible time standard
6) Mass
The masses of atoms can be compared with one another more precisely than they can be compared
with the standard kilogram. For this reason, we have a second mass standard. It is the carbon-12 atom,
which, by international agreement, has been assigned a mass of 12 atomic mass units (u). The relation
between the two units is
1u=1.660∗10−27kg
with an uncertainty of ±10 in the last two decimal places. Scientists can, with reasonable precision,
experimentally determine the masses of other atoms rela- tive to the mass of carbon-12. What we
presently lack is a reliable means of extending that precision to more common units of mass, such as a
kilogram.
7) Density
As we shall discuss further in Chapter 14, density r (lowercase Greek letter rho) is the mass per unit
volume: m/V Densities are typically listed in kilograms per cubic meter or grams per cubic centimeter.
The density of water (1.00 gram per cubic centimeter) is often used as a comparison. Fresh snow has
about 10% of that density; platinum has a density that is about 21 times that of water.
m
φ=
v
Review & Summary
Measurement in Physics
Physics is based on measurement of physical quantities. Certain physical quantities have been
chosen as base quantities (such as length, time, and mass); each has been defined in terms of a
standard and given a unit of measure (such as meter, second, and kilogram). Other physical
quantities are defined in terms of the base quantities and their standards and units.
SI Units The unit system emphasized in this Notes is the International System of Units (SI).
Standards, which must be both accessible and invariable, have been established for these base
quantities by international agreement. These standards are used in all physical measurement,
for both the base quantities and the quantities derived from them.
, Changing Units Conversion of units may be performed by using chain-link conversions in which
the original data are multiplied successively by conversion factors written as unity and the units
are manipulated like algebraic quantities until only the desired units remain.
Length The meter is defined as the distance traveled by light during a precisely specified time
interval.
Time The second is defined in terms of the oscillations of light emitted by an atomic (cesium-
133) source. Accurate time signals are sent worldwide by radio signals keyed to atomic clocks in
standardizing laboratories.
Mass The kilogram is defined in terms of a platinum – iridium standard mass kept near Paris. For
measurements on an atomic scale, the atomic mass unit, defined in terms of the atom carbon-
12, is usually used.
Density The density r of a material is the mass per unit volume.
Important Measures and units
1.
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