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College Physics
Including particle kinematics, particle dynamics, fixed-axis rotation of rigid bodies, kinetic theory of gases, basics of thermodynamics, electrostatic fields in vacuum, conductors and dielectrics in electrostatic fields, steady magnetic fields in vacuum, magnetic field effects on currents and magnetic media, Battery induction and electromagnetic fields, etc.
Edited at 2023-11-01 20:53:49
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College Physics (Part 1)
Chapter 6 Electrostatic Field in Vacuum
Chapter 7 Conductors and Dielectrics in Electrostatic Fields
Chapter 8 Steady Magnetic Field in Vacuum
Chapter 9 Magnetic field versus current and magnetic media
subtopic
Chapter 10 Electromagnetic induction and electromagnetic fields
10-1 Basic phenomena and laws of electromagnetic induction
power supply
power electromotive force
definition
scalar
Direction: from inside to forward
Electromagnetic induction
Phenomenon
Induced current
induced electromotive force
Faraday's law of electromagnetic induction
i: induced electromotive force
inference
When there are turns, ×N
Induced current
The amount of electricity induced through any section of the loop over a period of time
The two can be transformed into each other
Do the questions
subtopic
10-2 Dynamic electromotive force
definition
The magnetic field does not change and the conductor moves
The non-electrostatic force that generates electromotive force is: Lorentz force
formula
dl is a short distance
Do the questions
1. Let’s examine a small distance first: d
2. About arcs: Add a line segment to form a closed curve
3. When judging the general direction, if there are two power sources, look at which power source is larger and which one is used as the conductor.
10-3 Induced electromotive force
definition
The magnetic field changes, but the conductor does not move
Maxwell's hypothesis
The changing magnetic field will excite points with closed electric field lines around it, which is called induced electric field or vortex electric field.
formula
10-4 Self-inductance and mutual inductance
10-5 Magnetic field energy
10-6 Maxwell’s electromagnetic field theory
10-7 Electromagnetic waves
Chapter 5 Basics of Thermodynamics
5-1 First law of thermodynamics
law
Endothermic
The system performs work externally
exothermic
The outside world does work on the system
Internal energy increment calculation
Calculation of calories
Heat capacity
The amount of heat required when the system temperature rises by 1K
Related to quality and process
Fixed volume, V remains unchanged
Constant pressure
Calculation of calories
Calculation of work
Yuan Gong
dA
Total merit
illustrate
1. S of the P-V curve = the amount of work
2. The amount of work is related to the process
3. Adiabatic process (does not absorb or release heat)
Q=0
4. V expands, A>0, doing positive work
To increase the internal energy of a thermodynamic system, we can absorb heat from the outside and do work on the system.
5-2 Equivalent process of ideal gas
Isobody process
External work done: V remains unchanged
Isobaric process
The graph is a straight line
Isothermal process
PV=constant
The graph is a curve
5.3 Adiabatic process
definition
graph line
Compare work: compare the areas of P-V graphs
5.4 Cycle process
feature
positive cycle
definition
clockwise
A=area enclosed by closed curve
The system does net work externally
hot
efficiency
reverse cycle
definition
Refrigerator
Cooling coefficient
Carnot cycle
concept
A cycle that works between two constant-temperature heat sources, that is, a cycle composed of two isothermal and two adiabatic processes.
image
efficiency
Cooling coefficient
illustrate
1. Comparative efficiency
Check if the two temperatures are the same
2. More endothermic
3. More exothermic
5-5 Second Law of Thermodynamics
Question: Is there any restriction on the condition of "not causing other changes"?
Kelvin
It is impossible to absorb heat from a single heat source and convert it completely into useful work without causing other effects
This is true if there is no qualifying condition of "no other impact"
Clausius
It is impossible to go from low to high without having an impact
substance
1. All actual processes related to thermal phenomena are irreversible
2. In fact, any statement of an irreversible process is the second law of thermodynamics
significance
From a macro perspective, it always proceeds in the direction of increasing thermodynamic probability.
Chapter 4 Kinetic Theory of Gases
4-1 Ideal gas equation and several concepts
several concepts
state parameters
V (volume)
P (pressure)
T (temperature)
equilibrium state
P, T are equal everywhere
ideal gas equation of state
R: Universal gas constant = 8.31J/(mol*k)
First
another form
4-2 Molecular velocity distribution rules
gas distribution function
N is the total number of molecules, dN is the number of molecules in an interval, the ratio between the two is the percentage, and v is the rate.
physical meaning
Near v, the number of molecules within the unit rate interval accounts for the percentage of the total number of molecules
normalization condition
Maxwell's molecular velocity distribution law
Pay attention to the curve
Three rate statistics
most probable rate
The percentage of molecules with a velocity near V0 is the largest
average rate
The arithmetic mean of the velocities of a large number of molecules
root mean square rate
The square root of the average squared velocity of a large number of molecules
The relationship between the three
a. size:
b. Same gas at different temperatures: the one with the higher velocity has the higher temperature
c. Different gases at the same temperature: proportional to
4-3 Microscopic explanation of pressure and temperature
micro explanation
ideal gas pressure
The result of constant collision of large numbers of molecules against the walls of the container
formula
n is the number of molecules per unit volume n=N/V
m is the mass of a molecule
make
The average translational kinetic energy of gas molecules reflects the intensity of molecular motion
It is the average result of constant collisions of a large number of molecules and is meaningless for a small number of molecules.
temperature
Nature
1. It reflects the intensity of the irregular thermal motion of molecules.
2. T=0 is impossible to reach
Do the questions
1. Conversion unit
2. sequential formula
3. column formula
4-4 Theorem of equipartition of energy according to degrees of freedom Internal energy of ideal gas
internal energy of ideal gas
= Energy of all molecules Potential energy between molecules
only related to temperature
degrees of freedom
concept
The independent numbers required to determine the position of an object in space
degrees of freedom of gas molecules
a. There are 3 monatomic molecules
b. diatomic molecule
Center of mass (the center of the line connecting two atoms): 3
Connection direction: 2
Five in total
c. Triatomic molecules: 6
Calculated based on three-dimensional coordinate system
Theorem of equipartition of energy according to degrees of freedom
The average kinetic energy of a molecule is equal in every degree of freedom
average total energy of a molecule
i is the number of degrees of freedom
illustrate
single atom
Diatomic
three atoms
Chapter 3 Fixed axis rotation of rigid body
3-1 Angular description
rigid body
concept
an object whose size and shape always remain the same
Translational motion
The line connecting any two points in a rigid body always remains parallel during its motion.
v and a at any point in this motion are the same
turn
non-fixed axis rotation
The axis rotates with the object
Fixed axis rotation
The axis does not move
Features
I.
II. The relationship between angle quantity and line quantity
3-2 Law of Fixed Axis Rotation
Torque
d represents the vertical distance from the line of action of the force to the z-axis
Moment of inertia
Influencing factors
quality
shaft position
mass distribution
The farther the mass distribution is from the axis of rotation, the greater the moment of inertia is.
Several special moments of inertia
A.
B.
Thin rod
C.
ring
D.
disc
3-3 Conservation of angular momentum
Angular momentum of a rigid body about the axis of rotation
conservation
When M=0 (even if J keeps changing, it is still conserved)
Do the questions
1. Select the system. When colliding, give priority to the conservation of angular momentum.
2. Analyze separately, and whether M=0
3. applying its formula
kinetic energy
conservation of mechanical energy
There are only conservative forces in a rigid body
Chapter 2 Particle Dynamics
2-1 Newton’s laws of motion
1. F=ma
2-2 Application of Newton’s Laws of Motion
2-3 Law of momentum and conservation law
law of momentum
Definition: p=mv
Momentum Law of Points
Apply the momentum theorem to each particle, and then perform the summation
conservation law
2-4 Angular Momentum Theorem
Generally used in rotation
concept
The same particle, relative reference system, has different angular momentum
Torque
concept
definition:
Have the willpower
No matter where it is, if it always experiences the same force (or always points to a certain center), it is called a conscious force.
When receiving mental force, M=0
The angular momentum of the particle (that is, calculated by integrating)
theorem
conservation law
For example, when receiving mental force: M=0, then L1=L2
Note: Angular momentum is not the same as momentum!
2-5 work kinetic energy kinetic energy theorem
achievement
Current:
r is the displacement
work of curve
Get points
kinetic energy
law of kinetic energy of particles
The kinetic energy theorem of a system of particles
particle system
internal force
external force
Ideas
Sum the kinetic energy of each particle
When the sum of internal forces = 0, the work done by the internal forces is not necessarily 0. Eg: When there is relative displacement
2-6 Mechanical energy
four forces
gravity
gravity
Elasticity
conservative force
It has nothing to do with the path, only the beginning and the end
potential energy
definition
relative displacement between objects
conservation of mechanical energy
From the kinetic energy theorem, we can get
Conservation time
Chapter 1 Particle Kinematics
1-1Particle reference system and coordinate system
1-2 Description of particle motion state
position vector
r=xi yj zk
Directional cosines: cosα=x/r, cosβ=y/r, cosγ=z/r
Equations of motion
Describes the process by which the spatial position of a particle changes with time
r=x(t)i y(t)j z(t)k
speed
Average speed: V=rB(t △t)-rA(t)/△t=△r/△t
Instantaneous speed: V= dr/dt (find the derivative of displacement)
Average speed: ds/dt (derivative of distance)
acceleration
Average acceleration: a=△v/△t (△v is the time interval)
Instantaneous acceleration (also called acceleration): dv/dt (derivative of velocity)
Angular quantities in polar coordinate system
Angular displacement: θ
Angular displacement: △θ
Angular velocity: ω=dθ/dt
Unit: rad/s
Relationship with speed: w=πn/30
several formulas
Angular acceleration: β=dw/dt
ω=ω0 βt
△θ(θ-θ0)=wt
W2=w02 2β△θ
The relationship between angle quantity and line quantity
v=Rw
an (normal acceleration) = RW2
at (tangential acceleration) = Rβ
relative motion
several concepts
fixed frame of reference, moving frame of reference
The quantity of the fixed system of the particle pair: r absolute
Particle relative to the dynamic system: r
The traction of the dynamic system to the fixed system: r
The relationship between the two: r absolute = r relative r traction
Mechanics