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All AP Physics Concepts 226
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Gravity
Key Concepts:
Terms in this set (226)
What two entities comprise a vector?
Magnitude and direction
What do you do with any vector that is not on either the x or y axis?
Break it up into x and y components using trig, add up the components.
How are velocity and speed different?
Velocity has a direction and speed does not have direction.
What quantity is calculated from slope of the displacement versus time graph?
velocity
What does upward slope on a displacement versus time graph imply about the velocity.
The velocity is positive
What is acceleration?
How quickly you change velocity.
What is the area under the velocity time graph?
Displacement
What is the y intercept of the velocity time graph?
The initial velocity, (Vo in the formulas)
What is the area under the acceleration versus time graph?
The CHANGE in velocity.
What is the horizontal acceleration of projectiles?
ZERO
What direction controls time in falling body and projectile motion problems?
Vertical direction
What do you know about two objects that are launched at different horizontal velocities?
They fall, vertically, the by the same amount in the same time.
What equation describes the distance that a dropped object falls "t" seconds after it started moving?
x=(1/2)at^2 Remember, the word "dropped" implies no initial velocity.
What equation describes the distance that a horizontally launched projectile falls t seconds after it started moving?
x=(1/2)at^2 ...Horizontal velocity does not affect the time of fall.
What equation describes the speed of a dropped object "t" seconds after it started moving?
V=Vo + at ...The word "dropped" means no initial velocity.
What equation describes the speed in the x-direction of a projectile "t" seconds after it started moving?
Vx=(Vxo)t ...Recall that there is no acceleration in the horizontal direction.
What equation describes the speed in the y-direction of a projectile "t" seconds after it started moving?
Vy=Vyo + gt ...Watch the signs.
What is implied when an object is not accelerating in the x direction?
The body is moving at a constant velocity
What is implied when an object is not accelerating in the y direction?
g=zero so h=(Vyo)t
When is sum of force (net force) zero.
When a body is moving at a constant velocity or not moving at all.
When is sum of force (net force) NOT zero.
When a body's speed is changing.
What force is always present, and what is its equation?
Weight ...w=mg
How is sum of force (net force) depicted in a free body diagram?
It is an arrow that DOES NOT touch the body. Recall that the net force is the answer when all the forces are added up.
When is a normal force present, what is its direction?
When the body rests on a surface.
What is the component of "mg" parallel to a slope?
(mg)sin(angle)
What is the general equation for motion down a slope and how does it change if the object is going up the slope?
x=Vo + ((1/2)g)sin(angle)t^2
In uniform circular motion, how is tangential velocity calculated?
2(pi)R/T ...Circumference/Period
What is the direction of the centripetal force?
The centripetal force points along the radius towards the center of the circle.
What is the direction of the centripetal acceleration?
The centripetal acceleration points along the radius towards the center of the circle. (Just like the centripetal force.)
How is the centripetal force represented in a free body diagram?
It is the net force pointing towards the center.
A ball rolls inside a salad bowl. The ball is released along the top edge and rolls down before climbing to the same height on the opposite side of the bowl. What is the direction of the acceleration of the ball when it at the top edge of the bowl?
It is towards the center and downwards a little. It is the sum of the normal force perpendicular to the bowl and the weight downwards.
A ball rolls inside a salad bowl. The ball is released along the top edge and rolls down before climbing to the same height on the opposite side of the bowl. What is the direction of the acceleration of the ball when it at the bottom of the bowl?
The acceleration is towards the center. It is supplied by the normal force and points towards the center.
Mathematically what does centripetal force represent and how is centripetal force calculated?
The centripetal force is the net force. It's magnitude is calculated from F=ma where "a" is the centripetal force.
How is a force's direction oriented compared to a bodies direction of motion to get a circular (curved) path of motion?
The force is perpendicular to the motion to get a circular path of motion. (Think about centripetal force.)
How much work is the work done on an object moving in a circle? Why?
Zero. Because the displacement is perpendicular to the force (centripetal force.)
If you double the mass of one planet, triple the mass of another, and move them twice as far apart, what happens to the force of attraction between them?
The new force is 2/4 or 1/2 times the old force. ...Because the force of gravity varies directly with the masses and inverse squared to the distance apart.
What is the derived equation for the ACCELERATION of gravity in terms of m and "r" squared?
G(M:earth)/r^2 ...force of gravity = G(M:earth)(M:body)/r^2
How can total momentum be calculated?
Adding the momentum of all the bodies.
What is the difference between elastic and inelastic collisions? State the relevant equations for each.
kinetic energy is conserved for an elastic collision and not for an inelastic collision. ELASTIC: m1v1 + m2v2 = m1v1'+m1v2': INELASTIC: m1v1 + m2v2 = (m1+m1)v
What is impulse?
Impulse is the change in momentum
How does impulse relate to force?
Impulse is (force)(time)
What is a key requirement in order for work to be done?
A displacement must occur. ( W=Fd)
Work is the area under which curve?
The graph of force vs displacement
What is work energy theorem and what is its significance?
Work is the change in kinetic energy. Work transfers energy to and from a body
What is conservation of energy and what is its significance?
Sum of all the energy forms before a condition equals the sum of all the energy forms after the condition.
What is the energy equation if you see a height difference between two points in the problem?
Potential energy stored in gravity (PE = mgh)
What is the energy equation if you see a particle accelerated perpendicular to two charged plates, or the problem states that the particle is accelerated through a potential difference?
W=qV where "W" is the work, "q" is the charge and "V" is the potential difference measured in Volts.
What is Kinetic Energy lost and how is it calculated?
Lost kinetic energy is work. It is calculated from Fd or KE:final - KE:initial
What is the energy equation for the change in temperature if it results from a loss in KE?
KE=(3/2)kT where k is Boltzman's constant
What is the energy equation if a force (friction) through a distance results in heat and thus a change in temperature?
KE=Work
What is the relationship that describes the rate that work is done, or that energy is used?
Power ... Power equals the change in energy over time.
In a pendulum or spring, what are the displacement, velocity, PE and KE at the equilibrium position?
Displacement is zero because it is measured from equilibrium position. KE and velocity are at a maximum and it is the lowest point so PE due to gravity is at zero.
In a pendulum or spring, what are the displacement, velocity, PES, and K at maximum displacement?
This is the highest point of the swinging motion. PE is at a maximum. Displacement is the greatest from equilibrium. KE and Velocity are zero.
What do the period of pendulums and springs each depend on?
Pendulums depend on the length of the arm and the pull of gravity. springs depend on mass and the spring constant.
What is temperature?
The measure of the average kinetic energy of the molecules.
What is internal energy?
The motion of the molecules in gas.
What is an indication of a change in the internal energy?
A change in the gas' temperature.
What is heat?
The transfer of thermal energy
What is meant by the terms system and environment?
system is the gas being studied. Environment is the surroundings outside the gas.
What are the two forms of the ideal gas law?
PV=nRT and PV=kT
What is the 1st law of thermodynamics as applied to gases.
dU = Q+W ...dU:of the environment = Q:from the environment + W:by the environment
What is an isothermal process, and what is its impact on the first law of thermodynamics?
The PVT conditions change for a gas without changing the temperature.
What is the impact on the first law of thermodynamics for an isothermal process?
dU = zero. The change in temperature of the gas is zero.
What is an adiabatic process?
An adiabatic process is where no thermal energy is transfered between the system and its surroundings.
What is its impact on the first law of thermodynamics of an adiabatic process?
Q=0 because thermal energy is not transfered between the system and its surroundings
What is the area under any PV curve?
Work done "BY" the gas.
Under what conditions is mechanical work positive?
Work is positive when the force and displacement point in the same direction.
Under what conditions is mechanical work negative?
Work is positive when the force and displacement point in the same direction.
Under what conditions is work by a system ( gas) positive?
Work by a system is positive when the gas expands. (The volume increases.)
Under what conditions is work by a system ( gas) negative?
Work by a system is negative when the gas contracts. (The volume decreases.)
Under what conditions is heat positive?
Heat, (the "Q" variable), is POSITIVE when thermal energy is being ADDED to a system.
Under what conditions is heat negative?
Heat, (the "Q" variable), is NEGATIVE when thermal energy is being REMOVED from a system.
How is the net work of a system (gas) measured?
The NET work BY a system is the area enclosed in a cycle on a PV diagram.
What is the second law of thermodynamics?
Statistically speaking, energy flows from hot to cold.
Describe the relationship between Qh, Qc, and W in a heat engine?
Work of a system is equal to 1-Qc/Qh
How can you tell when an engine is a Carnot Engine?
The engine's efficiency is 1-Tc/Th. It is defined by the temperature's in the reservoirs and not the thermal energy flowing from them.
Under what conditions does entropy increase?
Entropy always increases.
What are 2 key differences between electric force and gravitational force?
The electric force (Coulomb's Law) can attract and repel and it depends on charge. Universal Gravity depends on mass and always attracts.
In electrostatics, what takes the place of m and g in the formulae?
"m" is replaced by "q," and "g" is replaced by "E." W=mg is replaced by F=qE. The second formula describes the force on a charged particle in uniform electric field.
If you have two charges, and you double one charge and triple the other, and move them twice as far apart, what happens to the force of attraction / repulsion between them?
According to Coulomb's Law, the new force is 6/4 times the old charge.
What is the derived equation for the electric field in terms of q and r^2 ?
E=kq/r^2 This is the electric field's magnitude at a point in space.
What is the difference between the variable "q" and "Q?"
"q" is a single particle's charge and "Q" is the sum of all the charges. Q=q1+q2+q3+q4...
What is the electric field's magnitude inside of a container made from an electrical CONDUCTOR?
Zero.
What is the electric field's magnitude inside of a container made from an electrical INSULATOR?
Something other than zero.
What does the term potential difference mean?
Potential difference is the change in energy of a charged particle divided by its charge.
What is the potential energy of a charge in an electric field?
V=kq/R
What does the term electric potential energy mean?
Electric potential is the potential energy associated with the electric force F=qE
What are three ways to increase the capacitance of a capacitor?
C=kEA/d: Increase the area of the plates, decrease the distance between the plates,and increase the dielectric constant between the plates.
What forces charges to move?
The electric field forces charges to move.
What do batteries and generators produce?
A potential difference and a flow and energized charges.
What is the actual movement of charges, and how is it measured?
The movement of charges is the current and it is measures by the number of charges per second at a point.
What causes resistance?
Obstacles in the path of the flow of charges.
How does a wires composition effect resistance?
But placing more obstacles in the path of the charge's flow.
How length effect resistance?
The longer the length of wire, the higher the resistance.
How does thickness effect resistance?
The thicker the wire, the lower the resistance.
How does temperature effect resistance?
The higher the temperature the higher the resistance. They are proportional to each other.
What is the relationship between voltage, current and resistance?
Ohm's Law: V=IR
What is the relationship between power, voltage and current?
P=IV
What quantity stays the same for resistors in series?
Current stays the same for resistors in series.
What quantity ADDS for resistors in series
Resistance: R=R1+R2+R3+...
What stays the same for resistors or capacitors in parallel?
Change in voltage across the resistor or capacitor.
What stays the same for capacitors in series?
The charge on each capacitor.
What kind of capacitor circuit adds to find the total capacitance?
Parallel. Because the plates are shared.
What is the path of a charged particle in a magnetic field?
The particle travels in a circle. Radius=momentum/qB
How is the force on a charged particle in a magnetic field creating the path calculated?
The force is perpendicular to the motion. This always results in a curved path. (Open right hand rule)
What is the work done on a charged particle by the magnetic field? Why?
ZERO. Because the force is perpendicular to the displacement . (Open right hand rule.)
How is the magnitude of the force on a current carrying wire calculated?
F=Bilsin(theta) ...F=Force (N), B:=magnetic field (T), i=current (A), l=length of wire in the field (m), theta is the acute angle between the field and current's directions.
How is the direction of the force on a current carrying wire calculated?
Open right hand rule
What is electromagnetic induction?
Electromagnetic induction is the generation of an Emf by moving a conductor through a magnetic field. emf=change in flux/dt
What is needed for electromagnetic induction to occur?
Electromagnetic induction occurs when a conductor is moved through a magnetic field such that a component of the fields is perpendicular to the current;s direction.
What is the difference between emf and voltage?
Emf is the maximum available energy per charge at the terminal of a power source. Voltage is the actual available energy per charge at the terminals of a power source. Some energy is lost due to the source internal resistance.
What is the formula relating emf and voltage?
V=E - IR V=terminal voltage (Volts), E = emf: electromotiveforce (Volts), IR = Internal drop in energy per charge (Volts)
How does the closed right hand rule work in electromagnetic induction?
It is used in Lenz's Law to determine the change in flux of a conductor.
What is the difference between a motor and a generator?
A motor uses energy to spin the coils in a magnetic field. A generator spins the coils to create an potential difference.
What are the differences and similarities between transverse and longitudinal waves?
Transverse waves: The displacement is perpendicular to the wave's motion. Longitudinal waves: The displacement is in the direction of the wave's motion.
Give an example of a transverse and a longitudinal wave.
Longitudinal Wave: Sound wave, Transverse Wave: Light wave, "The Wave" in a a crowd at a porting event.
What is the relationship between speed, frequency, and wavelength?
wave speed = (wavelength)(frequency)
What is the relationship between energy, frequency, and wavelength in any wave?
E=hf=hc/(wavelength)
How is tube length and wavelength related for a tube that is opened on both ends?
Only 1/2 a wavelength fits in the tube. L=wavelength/2
How is tube length and wavelength related for a tube that is closed on ONE end?
Only 1/4 wavelength fits in the tube. L=wavelength/4
What cause an electromagnetic wave, and what makes the wave propagate indefinitely even in a vacuum?
The interaction between an oscillating electric magnetic fields that are oriented 90° to each other. It propagates indefinitely because the wave takes its own medium.
What is the order of the electromagnetic spectrum?
Radio, Infrared, Visible, UltraViolet, X-Rays, Gamma Rays.
What is the order of the visible range electromagnetic spectrum?
ROY-G-BIV: Red, Orange, Yellow, Green, Blue, Indigo, Violet
What is the difference between reflection, refraction, and diffraction?
Reflection is the bouncing of waves. Refraction is the bending of waves. Diffraction bends waves around small objects and causes interference from a coherent sources.
Define reflection
The bouncing of light
Define Refraction
The bending of light
Define diffraction
Bends waves around small objects and the interference of waves from a coherent sources.
What is the law of reflection?
The Law of reflection states that the incident angle of a wave is equal to the reflected angle.
Define Snell's law.
(n1)sin(theta1) = (n2)sin(theta2)
What happens at the critical angle?
The refracted light ray is bent 90°. (Parallel to the interface surface.)
When light travels from LESS dense to a MORE dense mediums, how does the refracted ray bend in relation to the normal line.
LESS to MORE dense, the refracted ray bends TOWARDS the normal line.
When light travels from MORE dense to LESS dense mediums, how does the refracted ray bend in relation to the normal line.
MORE to LESS dense, the refracted ray bends AWAY from the normal line.
How must the mediums light is traveling through be arranged so that the condition for the critical angle can exist?
Light must travel from more to less dense so the refracted ray can bend away from the normal.
What doesn't change (speed, frequency, or wavelength), when light moves from one medium to another?
frequency (Think of the color as not changing.)
What conservation law dictates that the frequency of light cannot change as it travels between mediums?
Conservation of Energy ... because E=hf
What conditions are necessary to change the reflected ray's phase by 180°?
A reflected ray's phase is changes by 180° when the ray is bounced as it tries to travel from a lower to higher index of refraction. It is also changed y 180° when it bounces off of shiny surfaces.
What shapes are converging lenses?
Lenses that are fatter in the middle than on the edges.
What shape is a diverging lenses?
Lenses that are thinner in the middle than on the edges.
What shape is a converging mirrors?
Concave mirrors are converging mirrors.
What shape is a diverging mirror?
convex mirrors are diverging mirrors.
Which type of lenses have a POSITIVE focal length?
Converging lenses have a positive focal length.
Which type of lenses have a NEGATIVE focal length?
Diverging lenses have a negative focal length.
What are the two rules for ray tracing in lenses that work all the time?
(1) Straight through the vertex. (2) Parallel then through the primary focus.
What are the three rules needed for mirrors, since not all three work every time?
(1) Bounced off the vertex. (2) Parallel the through the focus. (3) Through the focus and parallel.
Which kind of lens always has a virtual image?
Diverging
Which kind of mirror always has a virtual image.
Convex
Which kind of mirror can show a real image?
Concave
Which kind of mirror cannot magnify an image?
Convex
What makes an image "real?"
The light travels through the image.
When are f, p, q, ho, hi, and M positive for mirrors?
When the object is beyond the focus for a concave mirror.
What kind of image do you get when the object is placed at the focus?
No image.
What kind of mirror has a positive focus?
Concave
What is an object placed when the distance between it and the mirror is positive?
In front of the mirror, in the light.
What two things must be true for a positive magnification?
(1) The image is larger than the object: ho>hi. (2) image is upright.
When is the image negative for mirrors?
When it is on the "dark" side of the mirror. Opposite the light.
When is the image negative for a lens?
When it is on the same side as the image?
What is Huygen's Principle?
Every point on a wave front is a secondary source.
State the significance of Young's Experiment.
Provided experimental proof of the wave property of light.
What does the pattern look like in a Young's Double Slit diffraction pattern?
Dark in the middle and alternating light and dark spots after that.
What does the pattern look like in a Young's Single Slit diffraction pattern?
Broad bright spot in the middle and alternating dark and light spots to the sides.
What did Thompson discover?
The electron
What did Rutherford discover?
The nucleus
What is the Bohr Model of the atom?
That the orbits of the electrons are like planets around the Sun.
What is the energy of a photon?
E=hf ...E=energy of a single photon (J), h = Plank's constant, f=frequency (Hz)
What is mass energy equivalence?
Energy and mass are equated by E=mc^2.
What does light absorption involve?
The incoming light (electromagnetic wave) has the same frequency as some of the electrons.
What does light emission involve?
Electromagnetic wave exits the electrons to a higher orbital. When the electron relaxes, a wavelength of light is given off.
What is ionization energy and how does it compare to the work function?
The work function is a minimum amount of energy needed to release a photon from a collection in the surface of a material. The ionization energy is the energy needed to release an electron from a single, free-floating, molecule. the ionization energy is higher than the wave function.
What is the photoelectric effect?
It is the release of photoelectrons released by photons with an energy (E=hf) above the work function.
What is the difference between atomic number and atomic mass number?
Atomic number is the number of protons. Atomic mass number is the number of nucleons, (protons and neutrons.)
How do you find the number of neutrons in an atom?
Atomic mass number minus atomic number.
What is an isotope?
Same number of protons by a different number of neutrons. e.g. Carbon-12 versus Carbon-14
What is the binding energy?
The energy required to remove an electron or nucleon from a molecule.
What is the strong force?
THe force that holds the nucleus together.
What causes radioactivity?
The release of a particle or photon from an UNSTABLE nucleus.
What is transmutation?
It is when a nucleon changes properties. Like a neutron changing into a proton.
What are the three types of radiation?
Alpha, Beta, and Gamma
What comprises alpha radiation?
The release of a Helium nuclei, 4,2 He2+
What comprises beta radiation?
The release of an electron and antineutrino or the release of a positron and a neutrino.
What comprises gamma decay?
The release of an energetic photon from an overly excited molecule.
Which type of radiation has the lowest energy?
Alpha
Which type of radiation has the highest energy?
Gamma
What is half life?
It is the time for 1/2 a substance to decay by radioactive processes.
What is force times the perpendicular distance?
Torque
What is force times the parallel diplacement?
Work
What is force times time?
Impulse
What is the name given to the distance between the pivot point and applied perpendicular force?
Moment arm
Define mass in terms of density.
m=(rho)V
S.I. unit of pressure
Pascal
This is the gauge pressure when under water.
(rho)gh
Continuity equation
a1v1=a2v2
How does the speed change when the pressure is decreased?
Speed ups
Pressure of an open container at the opening.
atmospheric pressure
This is used to determine the speed of a fluid when the pipe slopes up or down.
Bernoulli's equation
Flow Rate
Volume/time
Flow Rate
(Cross-sectional Area)(Velocity)
Buoyancy
Force lifting a body when it is in a fluid.
The "V" is (rho)Vg
The volume under water
Force in terms of pressure
Force= Pressure/Area
Condition for no rotation
Sum of the torques equal zero.
The speed of a ball when it lands at the same height it was thrown from.
initial velocity
S.I. unit of torque
N•m
S.I. unit of flux
Weber
S.I. unit of Flow rate
m^3/s
S.I. unit of work
Joule
S.I. unit of every kind of energy
Joule
S.I. unit of power
Watt
S.I. unit of momentum
kg•m/s
Unit that means the same thing as Nm
Joule
S.I. unit of centripetal force
Newton
S.I. unit of frictional force
Newton
S.I. unit of gravitational force
Newton
S.I. Unit of electric force
Newton
S.I. unit of magnetism
Tesla
Formula for work by a car that changes speed on a horizontal road.
W = KE:final - KE:initial
Formula for work as a charged particle travels across two charged plates
W=qV
Formula for the electric force felt by a charged particle in an electric field.
F=qE
Formula for the electric field between a pari of charged plates.
E=V/d
Unit of electric field
N/C
Unit of energy for electricity.
V ... Volt is a Joule/Coulomb
Energy of a SINGLE photon
E=hf
Average kinetic energy of an ideal gas's SINGLE molecule.
KE = (3/2)kT
Gauge Pressure
pgh ..thats ("rho")(gravity's acceleration)(height)
Formula for the potential difference of a point charge as compared to infinity.
V=kq/R
Formula for the electric field at point in space for a single point charge.
E=kq/R^2
Electric force felt by a charge due to another charge.
F=kq1q2/R^2
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