Physics Subject Area
Test
Basic Nature of Physics
* A scientific theory summarizes a hypothesis or
group of hypotheses that have been supported
with repeated testing.
* A law generalizes a body of observations. At
the time it is made, no exceptions have been
found to a law. Scientific laws explain things,
but they do not describe them.
*
*
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.
*
*Physics uses models that describe phenomena.
*A model is a pattern, plan, representation, or
description designed to show the structure or
workings of an object, system, or concept.
*A set of particles or interacting components
considered to be a distinct physical entity for
the purpose of study is called a system.
*
*Models help scientists develop hypotheses.
*A hypothesis is an explanation that is based on
prior scientific research or observations and that
can be tested.
*The process of simplifying and modeling a
situation can help you determine the relevant
variables and identify a hypothesis for testing.
Galileo modeled the
behavior of falling objects
in order to develop a
hypothesis about how
objects fall.
If heavier objects fell faster than slower ones,
would two bricks of different masses tied
together fall slower (b) or faster (c) than the
heavy brick alone (a)? Because of this
contradiction, Galileo hypothesized instead
that all objects fall at the same rate, as in (d).
*
* 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 group with an experimental group.
*
*
In SI, the standard measurement system for science, there
are seven base units.
*
Each base unit describes a single dimension, such as
length, mass, or time.
*
The units of length, mass, and time are the meter (m),
kilogram (kg), and second (s), respectively.
* Derived units are formed by combining the seven base
units with multiplication or division. For example, speeds
are typically expressed in units of meters per second
(m/s).
*SI Standards
*
In SI, units are
combined with
prefixes that
symbolize
certain powers of
10. The most
common prefixes
and their
symbols are
shown in the
table.
*
A typical bacterium has a mass of about 2.0 fg. Express
this measurement in terms of grams and kilograms.
Given:
mass = 2.0 fg
Unknown:
mass = ? g
mass = ? kg
*Sample Problem, continued
Build conversion factors from the relationships given in
the SI Prefixes Table. Two possibilities are:
1 𝑥 10−15 𝑔
1 𝑓𝑔
𝑎𝑛𝑑
1 𝑓𝑔
1 𝑥 10−15 𝑔
Only the first one will cancel the units of femtograms to
give units of grams.
(2.0 fg)
1 𝑥 10−15 𝑔
( 1 𝑓𝑔 )
= 2.0 𝑥 10−15 𝑔
*
*
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.
*
*
It is important to record the precision of your measurements so
that other people can understand and interpret your results.
*
A common convention used in science to indicate precision is
known as significant figures.
*
Significant figures are those digits in a measurement that are
known with certainty plus the first digit that is uncertain.
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.
*Rules for Determining
Significant Zeros
*Rules for Calculating with
Significant Figures
*Rules for Rounding in
Calculations
*
Tables, graphs, and equations can make data easier to
understand.
For example, consider an experiment to
test Galileo’s hypothesis that all objects
fall at the same rate in the absence of air
resistance.
In this experiment, a table-tennis
ball and a golf ball are dropped in
a vacuum.
The results are recorded as a set
of numbers corresponding to the
times of the fall and the distance
each ball falls.
A convenient way to organize the
data is to form a table, as
shown on the next slide.
*Data from Dropped-Ball
Experiment
*Graph from DroppedBall Experiment
*
* Oscilloscope
electrical equipment that allows
signal voltages to be viewed as a twodimensional graph
Voltmeter, ohmmeter, ammeter a
common electrical meter (multimeter),
capable of measuring voltage,
resistance, and current
Spectrometer an optical instrument
used to measure the properties of light
over a portion of the electromagnetic
spectrum
*
* Archimedes
* Greek mathematician, physicist, engineer,
astronomer, and philosopher
*
Law of levers
* Archimedes screw
*
Archimede’s Principle
Michael Farady
* English chemist and physicist
* Contributed to the fields of electromagnetism and
electrochemistry
* The “farad” - unit of capacitance
* Farady constant – the charge on a mole of electrons
*
about 96,485 coulombs
Sir Isaac Newton
* English physicist, mathematician,
* astronomer, alchemist, and natural philosopher
* Three Laws of Motion
*
1. Inertia
*
2. F=ma
*
3. Action/Reaction
*
Universal Law of Gravitation
Neils Bohr
* Danish physicist
* Understanding of atomic structure and
quantum mechanics
* Placed electrons in discrete orbits
around the nucleus
Determined chemical properties of
elements are largely due to the number of
electrons in the outer orbits
Originated the idea that photons are
emitted when electrons drop from a higher
energy orbit to a lower one
Received the Nobel Prize for Physics for
his work on quantum mechanics
Marie Curie
* Polish-French physicist and chemist
* Winner of 2 Nobel Prizes
* 1st woman to win a Nobel Prize
* Studied radioactive materials (pitchblende)
* Isolated and identified Polonium
*
*
and Radium
Albert Einstein
* German-born physicist
* Best known for the theory of
relativity
* and
the mass-energy
equivalence
Expanded Planck’s constant
(E = hv) to include “quanta”
Emax= hv-P
Gravity is no longer a force,
but a consequence of the
curvature of space-time
Robert Openheimer
* American physicist
* Best know for his role as the
director of the Manhattan Project
(effort to develop the first nuclear
weapons)
“The Father of the Atomic Bomb”
*
*
* strong force binds quarks together, strongest force, holds
neutrons and protons together, range theoretically infinite
*
mediated by gluons
* weak force - responsible for different types of particle decays,
including a process called beta decay
* Much stronger than gravity, but with a much smaller range
*
mediated by bosons
* Electromagnetism -binds negative electrons to the positive
nuclei in atoms and underlies the interactions between atoms
*
* Gravity
mediated by photons
- the attraction that any mass on any other object with
mass.
*
mediated by gravitons