Physics
The science that deals with energy, motion, matter, and force
Scientific Method
Characterizations, Hypotheses, Predictions, and experiments
Classical Physics
-Classical mechanics
-Thermodynamics
-Electrodynamics
Modern Physics
-Relativity
-Quantum Mechanics
Precision
The extent to which a given set of
measurements of the same sample agree with their
mean
Accuracy
The extent to which a given measurement agrees with the standard value for that measurement
Vector Quantity
Has magnitude and direction
Represented by an arrow
Ex: velocity, weight, force
Scalar Quantity
Has magnitude only
Ex: mass, volume, speed
Aristotle
Natural motion
Everything goes straight up or down
Beyond Earth, motion is circular
Galileo
Objects in free fall
Leaning tower experiment
-Objects of diff mass fall to the ground at the same time
-Demolished Aristotle's theory
Stated that objects remain in continuous state of rest unless acted upon by a force
Force
A push or a pull
Unit: Newton (N)
Vector quantity
Inertia
Property of matter to resist changes in motion
Depends on the amount of matter in an object
Newton
Formulated basic laws of mechanics
Discovered Law of Universal Gravitation
Invented calculus
Law of Inertia
Newton's first law of motion
"In the absence of external forces, an object at rest
remains at rest and an object in motion continues in
motion with a constant speed in a straight line"
Describes what happens in absence of force
Demo: coin drop in glass wh
Equilibrium
Net force is zero
Speed
Distance/Time
Velocity
How fast and in what direction
Vector quantity
Units: m/s
Acceleration
How quickly velocity is changing
Change in velocity/time
Units: m/s^2
Net force/mass
-If net force doubles, A doubles
-If mass doubles, A halves
Free Fall
9.8 m/s^2
v=gt
Velocity acquired in free fall from rest
d=1/2gt^2
Distance fallen in free fall from rest
Mechanical Equilibrium
When net force equals zero
Mass
Property of an object that specifies how much resistance an object exhibits to changes in its velocity
Unit: kg
Weight
Equal to the magnitude of the gravitational force exerted on the object
W = | m ?g |
Varies with location; is less at higher altitudes
Not an inherent quantity of an object
Unit: Newton (N)
Friction
Results from mutual contact of
irregularities in the surfaces of sliding objects
-Reduces net force
Law of Acceleration
Newton's second law of motion
Relates acceleration to force
"The acceleration produced by
a net force on an object is directly
proportional to the net force, is in the
same direction as the net force, and is
inversely proportional to the mass of the
objec
Law of Action-Reaction
Newton's third law of motion
"To every action there is always an equal and opp reaction"
Whenever one object exerts a force on a second object,
the second object exerts an equal and opposite force
on the first
-Forces always occur in pairs
Resultant
Sum of 2 or more vectors
Momentum
A quantity of movement
Mass*Velocity
Impulse
Force*Time
Change in momentum
> FT = >momentum
Law of Conservation of Momentum
Net mv (before) = Net mv (after)
Inelastic Collision
Collisions are accompanied by deformation and/or any generation of heat
Energy
The ability to do work
Involved in every physical process
Mover of substances
Both a thing and a process
A conserved quantity
Matter
Substance we can see, smell, and feel
Occupies space
Mechanical Work
The quantity of energy transferred by a force
Due to position or motion or both
2 forms: Potential and Kinetic
Work
Force*Magnitude of Displacement
W = Fd (force*displacement)
Unit: Joules (J)
2 things occur:
-application of force
-movement of something by that force
Something an object does, not has
Potential Energy
Stored energy held in readiness
-Could do work
Ex: stretched bow has stored energy that can do work on an arrow
Gravitational Potential Energy
Equal to the work done (force required to
move it upward the vertical distance
moved against gravity) in lifting it
PE=ma (mass
acceleration) due to gh (gravity
height)
=mgh
Kinetic Energy
Energy of a particle due to its motion
1/2mv^2
Quadrupled if speed is doubled
Scalar quantity--> always positive
Work-Kinetic Energy Theorem
W=KEi - KEf --> W= ? K E
Law of Conservation of Energy
Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy is always conserved (i.e. never
changes)
Ex: pendulum
Circular Motion
When an object turns about an internal axis
Characterized by 2 kinds of speed:
-Tangential (linear) speed
-Rotational (angular) speed
Rotational (Angular) Speed-->?
# of rotations per unit of time
Tangential (Linear) Speed-->v
Radial distance*angular speed
v=r?
Rotational Inertia
An object rotating about an axis tends to remain rotating about the same axis at the same rotational speed unless interfered with by some external influence
Ex: tight rope walker with pole
Rotational Inertia
The property of an object to resist changes in its rotational state of motion
Depends on mass and distribution of mass around axis
Greater when mass is located farther from axis
The greater it is, the harder it is to change its state
-Greater=slower
Torque
A measure of how much a force acting
on an object causes that object to rotate
-A twist to an object
Depends on magnitude of force, direction, and distance from the axis of rotation
Unit: N m
T = r
F (distance vector
force vector)
Centripetal Force
Any force directed towards a fixed center
"Center-seeking"
Ex: whirl can at end of string
Depends on mass, tangential speed, and radius
F = (mv2)/r
Law of Conservation of Angular Momentum
If no external net torque acts on a rotating system, the angular momentum of that system remains constant
Law of Conservation of Linear Momentum
If no external force acts on a system, the total
linear momentum of that system remains constant
Law of Universal Gravitation
Every body attracts every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance
separating them
-Everything pulls on everything else
F=Gm1m2/d^2
The greater the masses
G
Universal gravitational constant
6.67 x 10^-11 Nm^2/kg^2
Same everywhere
g
Acceleration due to gravity
9.80 m/s^2 at the surface of the Earth
Varies by location
Spring Tides
During the new moon or full moon, the effects of moon and sun add up
Higher-than-avg/lower-than-avg tides
Most pronounced
Neap Tides
When the moon is halfway between a new and full moon,
the tides due to sun and moon partly cancel each
Least pronounced
Range
Horizontal distance covered
Kepler's First Law
All planets move in elliptical orbits with the Sun at one focus
Kepler's Second Law
The radius vector drawn from the Sun to a planet sweeps out equal areas in equal time intervals
Kepler's Third Law
The square of the orbital period of any planet is proportional to the cube of the semimajor axis of the elliptical orbit
Aphelion
The point farthest away from the sun
a + c
For an orbit around the Earth, this point is called the apogee
Perihelion
The point nearest to the sun
a - c
For an orbit around the Earth, this point is called the perigee
Curvature of Earth
Earth surface drops a vertical distance of 5 meters for every 8000 meters tangent to the surface
Satellite
Projectile that falls around Earth
-Sufficient tangential velocity needed for orbit
Speed is constant, only direction changes
Unchanged by gravity
Fulcrum
Point of support on which a lever rotates
Archimedes Principle for Floating Objects
For floating objects, buoyant force is balanced by the weight of the floating object
-Also, the volume of displaced fluid is equal to the volume of immersed part of the object
Bernoulli's Principle
Pressure of a gas or liquid decreases as its velocity increases
Specific Heat Capacity
Quantity of heat required to change the temperature of a unit mass of the substance by 1 degree Celsius
-Water is high
-Metal is low
Anomalous Behavior of Water
As temp increases from 0C-4C, water contracts
-Density increases
Above 4C water expands with increasing temp
-Density decreases
Max density of water occurs at 4C
Add Energy
Solid --> Liquid --> Gas
Remove Energy
Gas --> Liquid --> Solid
Human Hearing Range
20 Hz - 200,00 Hz
Sound
Undergoes reflection and refraction
Musical Tone
Steady periodic sound
Pitch
Determined by lowest frequency
Intensity
Perceived loudness
Quality
Depends on relative intensity of harmonic partials
Electric Field
Inside a conductor always equals zero
Ohm's Law
Electric potential difference between one part of your body and another part depends on body condition and resistance
-100,000 ohms - 500,000 ohms
-Electric shock
Electric Power
Rate at which electric energy is converted into another form
Series Circuit
Electric current through a single pathway
-Total resistance to current is sum of individual resistances
-If one device fails, current stops
-Christmas lights
Parallel Circuit 2
Adding more laps produces:
-Less resistance
-Increase in current
-Lamps unchanged
Series Circuit 2
Adding more lamps produces:
-Greater resistance
-Decrease in current
-Lamps dim
Parallel Circuit
Voltage is the same across each device
-Total current = the sum of currents in its branches
-A break in one path does not interrupt flow of charge in other paths
-Lighting system in house
Magnetic Force
Force due to the charged particles
North Pole
Points to geographic north
Points to magnetic south
South Pole
Points to geographic south
Points to magnetic north
Magnets
All have 2 poles
Electromagnetic Waves
Do not need a medium to travel
Made up of vibrating electric and magnetic fields
Electromagnetic Spectrum
Radio, microwaves, infrared, visible, UV, x-ray, gamma
Shadow
Region where light rays do not reach
Selective Reflection
Objects reflect light of some frequencies and absorb the rest
-Objects that absorb light and reflect none appear black
-Objects can reflect only those frequencies present in the illuminating light
Selective Transmission
Color of transparent object depends on color of light it transmits
Magenta
Red + Blue
Complementary : Green
Cyan
Green + Blue
Complementary : Red
Yellow
Green + Red
Complimentary : Blue
Subtractive Primary Colors
Cyan, yellow, magenta
Colors
Pigments that produce red absorb cyan
Pigments that produce blue absorb yellow
Pigments that produce green absorb magenta
Reflection
When light is returned into the medium from which it came from
-Light takes the quickest (shortest) path in going from one place to another
Convex Mirror
Virtual image is smaller and closer to the mirror than the object
Curves out
Concave Mirror
Virtual image is larger and farther away than the object
Curves inward
Refraction
When light bends in going obliquely from one medium to another
-Changes speed as well as direction
Refractive Index (n)
Ration of speed of light in vacuum to speed of light in material
Rainbow
Results from refraction, dispersion, and internal reflection
Mirage
Refraction
Bohr's Model of Atom
Electrons occupy "stationary" states (of fixed energy,
not fixed position) at different distances from the nucleus
-Electrons can make quantum jumps from one energy state to another
-Light is emitted when such a quantum jump occurs from a higher to a lowe
X-rays
De-excitation of innermost orbital electrons
-Can penetrate many layers of atoms
-Produces higher frequency x-radiation
Alpha Waves
Positively charged
-Helium nuclei
-Originate in nucleus
Beta Waves
Negatively charged
-Electrons
-Originate in nucleus
Gamma Waves
No charge
-Electromagnetic radiation
-Originate in nucleus
Radioactive Decay
The rate of decay is measured in terms of the half life
Half-Life
The time it takes for half an original quantity of an element to decay
Frame of Reference
The place from which motion is observed and measured
Motion is Relative
An object may have different velocities relative to different frames of reference
First Postulate of Einstein's Law of Relativity
All laws of nature are the same in all uniformly moving frames of reference
Second Postulate of Einstein's Law of Relativity
The speed of light in free space is a constant in all inertial frames and is independent of the state of motion of the emitting body
Time Dilation
Moving clock ticks more slowly than stationary one
Length Contraction
Length contracts with respect to the stationary observer