Midterms Flashcards
scientific literacy
the set of skills & background knowledge necessary for being a competent scientist
primary goal of science
to describe the phenomena that make up the universe (including our world)
physics
the study of how the universe works, what the universe is made of, & how the universe is structured
scientific models
desc’s of the universe
- verbal desc’
- graphs/pics
- mathematical equations
- combos of the above
scientific law
the pinnacle of scientific desc
description of a phenomenon (relationship among varialbes) thought 2 be universal
usually mathematical
proportional reasoning
figuring out how a change in 1/more variables in an equation affects another variable
direct variation
when a change in 1 variable produces an equal change in another variable, we say that those 2 variables are “directly proportional”
inverse variation
when a change in 1 variable produces a reciprocal change in another variable, we say that they’re “inversely proportional” or that they “vary inversely”
general form L = 1/M
joint variation
Equation: c = 5ab
variable c is jointly proportional to a and b. means that c is directly proportional to both a and b
doubling a causes c to double
doubling b causes c to double
doubling bouth a and b causes c to quadruple
What 3 things does a measurement indicate?
magnitude
unit
property/quantity being measured
composite/derived property/quantity
prop’s/quant’s derived from (made up of) 2/more other quant’s
What kind of units do comp/derived prop’s/quant’s have?
composite units
composite units
units tht r actually made up of other, more fundamental units
how many fund prop’s r there?
7
fund prop’s/quant’s
prop’s that can’t be derived from other prop’s
fundamental unit
each fund quant has an associated fund unit in the International System(SI System) which is used almost worldwide in science
can’t be broken down in2 other units
fund units of length, time, & mass
length - meter m
time - second s
mass - kilogram kg
7 fund units
length
time
mass (how much matter)
temperature
electric current
amount (how many of something)
luminous intensity
base unit of mass
gram g
order of metric ladder
kilo, hecto, deca, base(gram, liter, sec, meter), deci, centi, milli
King Henry Died Monday Drinking Chocolate Milk
can u add measurements with diff properties & units?
no, but u can add measurements of diff units & same properties
unit + unit
unit
unit - unit
unit
unit * unit
unit2
can u multiply measurements of diff quantities & units?
yes
unita * unitb
unita(unitb)
distance
so fundamental, it’s diff 2 define w/out reference to distance, length, etc.
the total lenght of the path traveled by an object
time
also extremely fund
elapsed time is the duration b/w 2 events
instantaneous speed
speed @ a given point in time
the distance traveled divided by the time it took 2 travel that distance
s = d/t
average speed
total distance traveled divided by total time it took to travel that distance
the constant speed needed 2 cover the distance of the trip in the time of the trip
motion diagram
a series of images of a moving object that records its position after equal time intervals
particle model
replaces an object by a single point
size of the obj must be much less than the distance it moves
ignore internal mtions like waving of the arms
origin
the pt at which the variables have the value zero
position vector
locates the position of the object
lenght of position vector = proportional 2 the distance from the origin 2 the location of the moving obj @ a particular time
scalar quantity
a quantity that tells u only the magnitude of something
mass, time, temp, distance, speed
vector quantity
tells not only the magnitude of something, but also its direction
velocity, acceleration, position, force
displacement vector
drawn from the position of the moving @ an earlier time 2 its position @ a later time
time interval
>t = t1 - 10
average velocity
v = >d/>t
increases when d increases & t decreases
on PT graph, same as slope
instantaneous velocity
the speed and direction of an obj @ a particular instant in time
displacement
>x = d1 - d0
a change in position
d is always greater than/equal to |>x|
average acceleration
an object in motion whose velocity is changing is said to be accelerating
a = >v/>t
position
d1 = d0 + vt
location in space relative 2 a reference pt
includes distance & direction
mechanics
branch of physics concerned w/ motion
kinematics
branch of mechanics tht describes motion w/out considering the causes of motion
motion
a change in location/position of an obj over time
velocity & acceleration relationship
v a
increase speed
+ +
- -
decrease speed
+ -
- +
direction of motion & no motion (“at rest”) on VT graph
what regions indicate “slow” and what regions indicate “fast” on a VT graph
constant acceleration in pos. & neg. directions in VT graphs
constant deceleration in pos & neg directions on VT graph
equations to know
v = >d/>t
a = >v/>t
df = di + vt OR >x = vt
vf = vi + at OR >v = at
>x = 1/2 (vi + vf) t OR df = di + 1/2 (vi + vf) t
>x = vi • t + 1/2at2 OR df = di + vi t + 1/2at2
vf2 = vi2 + 2ax
ht(down/up) = [2x/a
ht(down & up) = 2[2x/a
free fall
when an object falls under the ifnluence of gravity alone
gEarth = ?
-9.81 m/s2
what lesson did scientists have to relearn?
our perception of motion can be influenced by how we observe it
acceleration
how velocity changes over time
explain or demonstrate why the unit for accel is m/s2
the units are m/s2 because acceleration is the change in velocity over time/per unit time. velocity has fundamental units of m/s and time has fundamental units of s, so acceleration = change in velocity/change in time yields units of m/s/s. this yields m/s2 as shown below: m/s/s = m/s • 1/2 = m/s2
celestial bodies
refer to those things we see beyond the earth, in the “heavens”
moon, sun, planets
what do some of humankind’s earliest recorded observations of motion concern?
cycles of sun, moon, stars
Ex: daily cycle of sun, 28 day cycle of moon, nightly & seasonal cycle of stars
instead of sci analysis, how were the movements of celestial objects explained?
based on religious ideas/primitive analogies w/ the kind of motions they observed around themselves
Ex: Greeks thought the Sun was a god who rose out of the ocean and drove a chariot across the sky
when were the 1st telescopes invented?
17th century (1600’s)
what were the early Greeks responsible for? when?
began developing systems of thought tht explained phenomena according to empirical/logical principles vs. religious ideas
5th & 6th centuries BC
2 early Greek philosphers
Thales of Miletus & Pythagoras
who developed the Greek understanding of motion? when?
Aristotle
384-322 BC Athens
for how long did the Greek understanding of motion dominate European thought abt motion?
more than 1,000 years
Aristotle’s understanding of motion
- All objects have a tendency to move toward their “natural” place, depending on what they’re made of (earth, water, air, fire)
- The Earth is @ the center of the universe & doesn’t move
- Sun, Moon, & planets moved in perf circles around earth (constant distance, speed, & direction)
- speed of obj’s to/from earth depended on weight
- any obj set in motion, on the earth & @ any rate, will eventually slow & stop. force necessary to keep it moving
on what was Aristotle’s understanding of motion based?
observations
logic & empirical principles
problems w/ Aristotle’s ideas
w/ observation, obvious tht the planets were sometimes closer 2 Earth than @ other times & tht they moved in their orbits @ varying speeds
how did Ptolemy try to make the observations of celestial motion fit Aristotle’s theory/explanation of motion
epicycles
said the planets also revolving in mini orbits
what did epicycles explain?
retrogade motion
planets appeared to move backwards sometimes
benefits of Ptolemaic system
explained curious motions of the planets
allowed for the prediction of the future positions
role of the Catholic church in promoting Ptolemy’s & Aristotle’s understanding of the structure of the universe
regarded by Church as “authorities” who, tho they lived in the pre-Christian era, had put forward doctrines tht contained divine wisdom
scholars who questioned these authorities might have publications of their books prohibited, or even been imprisoned/executed
why were philosophers, scientists, & Christian scholars disturbed by Ptolemy’s system (geocentric w/ planets orbiting on 1/more epicycles)
made the system jury-rigged, like a clunky machine fitted out w/ additional parts just to make it work properly
lacked the elegance & simplicity tht even the Christian scholars thought God’s work should reveal
who was William of Ockham
when was he alive
what was his important philosophical & scientific principle
Franciscan monk & Oxford scholar
1285-1349
“entities must not be needlessly multiplied”
Ockham’s/Occam’s Razor
when considering competing explanations, 1 chooses the simplest explanation (the one w/ the fewest assumptions) & is supported by evidence
when considering an explanation, u should suspect tht it’s false if it needs assumption/extra parts added to it over time to fit new data
what was Copernicus’ insight into the problem of retrograde motion & the reason y the Ptolemaic system was failing to accurately predict planetary positions
retrograde movement of Mars occurs cuz it has a larger orbit than earth, so earth sometimes passes it, making it look like it’s going backwards
from view of observer
what aspects of ptolemy/aristotle’s system did copernicus retain in his heliocentric system?
didn’t challenge the other Ptolemaic ideas of how planets moved @ constant speeds & in perf. circles
to explain, had to retain some of the epicycles
what did Kepler (1571-1630) realize abt the orbits of the planets around the sun?
the planets moved in elliptical, not circular, orbits
the planets moved faster the closer they were to the Sun & slower the farther away cuz Sun exerted some sort of force
effect of Kepler’s Laws of Planetary Motion
had provided the mathematical foundation for the acceptance of the Copernican theory of the solar system
now positions & movements of the planets could be calculated w/ a high degree of accuracy
why did the heliocentric view seem absurd to some ppl?
if earth was indeed moving thru space @ incredible speeds & spinning on an axis, y don’t we feel the motion/fall off?
what did Galileo demand of his students?
that they test their ideas thru experimentation & empirical observation
Galileo’s procedure for testing Aristotle’s ideas of motion?
used his pule (& other mechanisms such as water clocks) as a timer, and rolled objects of diff weights down inclined planes
what did Galileo find in testing Aristotle’s ideas abt motion?
- all obj’s near surface of the earth fall @ same rate of accel, regardless of weight
- force not required 4 motion. force doesn’t cause motion –> changes in motion
what argument did Galileo use to defend heliocentric view?
sailors on a ship can’t feel ship’s motion when moving @ constant speed on calm sea
in which book did Galileo put forth his argument?
Dialogue on the Two Chief World Systems, 1632
who was born same year galileo died
Isaac Newton (1642-1727)
galileo’s law of falling bodes
cumulative distance fallen is proportional to the square of time, and the distance fallen b/w each successive time interval increases according to the progression of odd #’s
contributions of Galileo
- all obj’s near surface of earth fall @ same rate of accel regardless of weight
- after initial impluse, an obj might move forever until opposed by another force (inertia)
- total distance fallen is proportional to t2
- the distance fallen b/w each successive time interval increases according to the progression of odd #’s
- telescope
- movement & surfaces of celestial bodies
- precise measurements to test ideas
force
a push/pull on an object
transferred from one object to another
causes change (direction/speed) in motion - does not cause motion
not necessary to sustain motion
vector quantity
inertia
responsiveness to force
no object(or their mass) can resist a force - only other forces can counter a force
indicated by mass: as mass goes up, inertia goes up, and acceleration responsivess goes down
if an obj is at rest, it tends to remain at rest. if it is moving at a constant velocity, it tends to continue moving at that velocity
Newton’s 2nd Law
f = ma
unit of force
Newton(N)
what equation can be derived from Newton’s 2nd law?
a = fnet/mass
2D vector adding
- put arrows head to tail MAKE SURE U DON’T CHANGE THEIR DIRECTION
- if @ right angles, Pythogorean Theorem
- if not right angle:
- form a parallelogram & then the diagonal coming from b/w the 2 vectors will be the resultant
- can also split bottom vector into horizontal & vertical components & join them w/ top vector, + the parallel vectors, put the remaining vectors back together @ right angle, & then use Pythogorean Theorem
if 3 motorboats crossing a river & motorboat a’s resultant is straight across, b’s is closest to opposite shore, and c’s is longest, then
a) which boat reaches the opp shore first?
b) which boat provides the fastest ride?
c) which boat takes the shortest path to the opp shore?
b
c
a
how to tell speed of resultant
length
weight
strength of the force of gravity on an obj
unit of measure = N/lbs
measured by spring scale
W = mg; W = mass•accel(from gravity)
depends on laction in a gravitational field
mass
measure of the amount of matter in an object
indicates inertia
measured by a balance
fundamental
unit = kg
would not differ on moon and Earth
mass = energy
how r weight & mass related
directly proportional
how r force & accel related?
directly
how r mass & acceleration related?
inverse relationship
when doing pulley & cart experiment, how do u calculate the acceleration?
force is the weight attached to the end of the pulley
mass is the mass of the weights @ end of pulley + mass of cart + any masses on cart
what r the fund units that make up a Newton (N)?
kg•m
_____
s2
net force
the vector sum of all forces acting on an object
something that disturbs the state of equilibrium/changes the velocity of an object
contact force
acts on an obj only by touching it
Ex: friction
long-range force
exerted w/out contact
Ex: weight
Friction (Ff)
the contact force that acts to oppose sliding motion b/w surfaces
parallel to surface & opp. direction of sliding
Normal (FN)
the contact force exerted by a surface on an obj
perp to & away from the surface
Spring (Fsp)
a restoring force, the push/pull a spring exerts on an obj
opp. the displacement of the obj @ the end of the spring
Tension (FT)
the pull exerted by a string, rope, or cable when attached to a body & pulled taut
away from the obj & parallel to the string, rope, or cable @ the pt of attachment
thrust (Fthrust)
a general term for the forces that move objects such as rockets, planes, cars, & ppl
in the same direction as the accel. of the obj barring any resistive forces
Weight (Fg)
a long-range force due to gravitational attractin b/w 2 obj’s, generally Earth & an object
straight down toward the center of the Earth
force of weight = force of gravity
common misconceptions
- when a ball has been thrown, the force of the hand tht threw it DOES NOT remain on it - it is a contact force & thrfore once contact is broken, the force is no longer exerted
- a force is NOT needed to keep an obj moving - if there’s no net force, then the obj keeps moving w/ unchanged velocity. if friction is a factor, then there’s a net force & the obj’s velocity will change
- inertia is NOT a force - forces r exerted on obj’s by the environ, they r not properties of obj’s
- air DOES exert a force (a huge force), but cuz it is balanced on all sides, usually exerts no net force unless an obj is moving
- the quantity ma is NOT force - the equals sign in F=ma doesn’t define ma as a force; rather, means that experiments have shown tht the 2 sides of the equation r equal
a ball is thrown straight up into the air
@ the very top of its trajectory of motion(just before it starts to fall back down) the net force on the ball is?
its weight
at the top, the only force acting on the ball is the force of gravity(same as weight)
how to calculate what friction force acts on a mass
Ex: A horizontal force of 5.0N accelerates a 4.0-kg mass, from rest, at a rate of 0.50m/s2 in the positive direction. what friction force acts on the mass?
- calculate normal force. F = ma → F = 4kg•0.5m/s2 = 2N
- Find the net force b/w 2N from previous step & given force (5N)
- 5N - 2N = 3N
equlibrium
an obj is in equilibrium if it’s @ rest or if it’s moving @ a constant velocity
net force = 0
Newton’s 1st Law of Motion
Law of Inertia
Any obj will remain @ rest/moving w/ uniform motion (constant speed AND constant direction) iff the net force acting on tht obj is zero.
OR
a net force acting on an obj will cause tht obj to accel (change its motion by changing its speed and/or direction)
a = f/m → responsiveness to force = net force/inertia
inertia
responsiveness of an obj to force
inertia & mass
the measure of an obj’s inertia is the obj’s mass
the more mass an obj has, the more inertia it has, & the less it responds to force
canceling a force
only a force can resist/cancel another force. mass(inertia) by itself can NOT resist force
when an obj appears to resist a force cuz it doesn’t accel in response 2 the force, always cuz another force is acting. usually friction
Greek philosopher Aristotle asserted that
force is required for motion
heavier obj’s fall faster than lighter obj’s
accel of an obj is due to
an unbalanced force acting on the obj
an obj following a straight-line path at a constant velocity must
have zero acel
still forces acting, just canceled out
on a VT graph, what tells u the instantaneous acceleration at any time?
slope
decreasing positive velocity on PT graph
decreasing neg velocity PT graph
increasing pos velocity PT graph
increasing neg velocity PT graph
on a VT graph, what tells you the displacement that occurred during the motion?
the area under the graph
relationship b/w accel & mass in newton’s 2nd law
inverse
relationship b/w accel & force in newton’s 2nd law
direct
you r sitting in the back seat of a car that is moving at a constant speed in a straight line. u hold a baseball directly above ur lap & drop it. the ball lands
in ur lap
cuz CONSTANT VELOCITY
u’re sitting in the back seat of a car that is moving @ a constant speed in a straight line. you hold a baseball directly above ur lap & drop it. just as u drop it, the driver of the car hits the brakes hard. the ball lands
ahead of ur lap
VELOCITY CHANGED
passenger in car moving in straight line @ constant speed
car turns sharply to left & u’re thrown against side door
when a passenger is wearing a seatbelt, basically share the same state of motion as the car. accelerate & decelerate w/ the car(except for internal organs & head)
when not wearing seat belt, separate obj’s w/ separate rates of motion. when the car abruptly changes direction, the passenger continues w/ the same velocity as before (until they hit the door)
Newton’s 3rd Law of Motion
for every force thr is an equal & opp reaction force
FAonB = -FBonA
action-reaction pair
the 2 forces involved
do not cancel each other out
“equal”
equal in magnitude
simultaneous - occur @ exactly same time & last for same amount of time
“opposite”
opposite in direction
180o
y don’t action & reaction forces cancel each other out?
they r usually acting on diff obj’s
where do u draw vectors?
on the obj receiving the force
Why does Bob beat Annie in tug of war?
based on newton’s 3rd law, they r both exerting the same amount of force, but Bob still wins cuz he is exerting more force on the ground
if the floor is exerting a reaction force back on u due to ur weight on it, then y don’t u get pushed into the air away from the floor?
gravity pushes u down
if a horse exerts a force on the cart & the cart exerts an equal but opp force on the horse, how can the horse move the cart?
more than just the 2 forces acting on them
also, the 2 forces r both acting on diff obj’s w/ diff masses
when can action-reaction forces cancel each other out?
if they r part of the same system & become internal forces
drawing tug of war vectors
rope on gm -> rope on gp <-
Earth on gm v gm on earth ^
Earth on gp v gp on Earth ^
gm on ground -> ground on gm <-
gp on ground <- ground on gp ->
gm on rope <- gp on rope ->
ground on gm ^ gm on ground v
ground on gp ^ gp on ground v
Work
exerting a force over a distance
when u exert a constant force on an object thru a distance, in the direction of the force, u do an amount of Work on the object
W = f•d
W is positive, & the energy of the obj increases by an amount equal to W
neg. work is done when exerting a force on an obj in the direction opposite to its motion
W = change in energy; work done on an obj + energy, an obj doing work - energy
kinetic energy
energy of motion
final KE = initial KE + W
K = 1/2mv2
Joules
gravitational potentional energy
GPE
if system b/w an obj & Earth, gravitational attraction b/w them = an interaction force. if obj moves away from Earth, energy = stored in the system as GPE as a result of the gravitational interaction b/w the obj & the Earth.
Ug = mgh
reference level
where the GPE is defined to be 0
random
energy
the ability to do work
amount of energy = amount of work possible
Joules
kg • m2
_______
s2
simpifies to F•d
force → energy
forces r responsible for changing energy from 1 form to another
they move energy from 1 obj to another as well
potentional energy
stored energy
often has to do with resisting some kind of force
energy equations
all come form F • d
Law of Conservation of Energy
as long as the system under investigation is closed so that the objects don’t move in & out, & as long as the system is isolated from external forces, then energy can only change from or be transferred
Kbefore + Ugbefore = Kafter + Ugafter
mechanical energy
E = KE + Ug
only if no other forms of energy r present
relationship b/w mass & energy
mass = energy
E = mc2
power
rate @ which energy is transferred/transformed
p = >E/>t
unit = Watt (W) = J/s = (kg•m2)/s2
\_\_\_\_\_\_\_\_\_\_\_ = (kg•m<sup>2</sup>)/s<sup>3</sup>
s
