bài giảng vật lý chất lượng cao

Kinematics : describe the motion of an object while ignoring the interactions with external agents  Motion in one dimension: motion of an object along a straight line  Particle model:

PHYSICS 1

PHYSICS 1 : MECHANICS AND THERMODYNAMICS

PHYSICS 2: OSCILLATIONS, ELECTRICITY AND MAGNETISM PHYSICS 3: WAVES, OPTICS AND MODERN PHYSICS

 Properties and laws of motion of particle, rigid body

 Relationship among position, velocity and acceleration

 Laws of linear momentum, angular momentum and energy

 The kinetic theory of gases, thermodynamic quantities

 Laws of Thermodynamics

5 Textbook

1. Raymond A Serway and W Jewett, Physics for Scientists and

Engineers with Modern Physics (9th Edition), Cengage Learning, USA, 2014

2. Tr n Ng c H i, Ph m Văn Thi u, ầ ọ ơ ạ ề V t lý đ i c ậ ạ ươ ng: Các

nguyên lý và ng d ng, T p 1: C h c và Nhi t h c ứ ụ ậ ơ ọ ệ ọ , NXB Giáo

d c 2006ụ

Reference Books

3. Hugh D Young and Roger A Freedman, University Physics with

Modern Physics (13th Edition), Pearson Education, USA, 2012

4. Paul A Tipler and Gene Mosca, Physics for Scientists and

Engineers (6th Ed.), W H Freeman and Company, USA, 2008

5. David Halliday, C s v t lý ơ ở ậ , t p 1, NXB Giáo d c, 2007ậ ụ

3 Solve problems of chapters 2, 3, 4 Prepare the solution of problems by group

4

Chapter 5: Circular motion and other

applications of Newton’s laws Read the text book: 150-167Chapter 6: Energy of the system Read the text book: 177-201 Chapter 7: Conservation of energy Read the text book: 211-233

6 Lesson plan

5 Solve problems of chapters 5, 6, 7 Prepare the solution of problems by group

6

Chapter 8: Linear momentum and

Chapter 9: Rotation of rigid object about

7 Solve problems of chapters 8, 9 Prepare the solution of problems by group

6 Lesson plan

9 Solve problems of chapters 10 Prepare the solution of problems by group

Chapter 12: Tempurature and the first

law of Thermodynamics Read the text book: 568-62510

Chapter 13: The kinetic theory of gases Read the text book: 626-652 Chapter 14: Heat engines, entropy and

the second law of Thermodynamics Read the text book: 653-688

11 Solve problems of chapters 12, 13, 14 Prepare the solution of problems by group

12 Represent the result of the project

Work in group to make the product of the project and to prepare a report of project

7 Assessment Plan

8 Student Responsibilities and Policies:

 Attendance: It is compulsory that students attend at least 80%

of the course to be eligible for the final examination

 Missed tests: Students are not allowed to miss any of the tests

There are very few exceptions

Assessment Types Assessment Components Percentages

A1 Learning activities

A1.1 Attendance A1.2 Homework report A1.3 Project

20%

PHYSICS AND

MEASUREMENT

CHAPTER 1

Physics, the most fundamental physical science, is concerned with the fundamental principles of the Universe

The study of physics can be divided into six main areas:

 Classical mechanics: concerning the motion of objects that are large relative to atoms and move at speeds much slower than the speed of light

 Relativity: a theory describing objects moving at any speed, even speeds approaching the speed of light

Thermodynamics: dealing with heat, work, temperature, and the statistical behavior of systems with large numbers of particles

Electromagnetism: concerning electricity, magnetism, and electromagnetic fields

Optics: the study of the behavior of light and its interaction with materials

 Quantum mechanics: a collection of theories connecting the behavior of matter at the submicroscopic level to macroscopic observations

Physics and measurement

Like all other sciences, physics is based on experimental observations and quantitative measurements

 Objectives: to identify fundamental laws governing natural phenomena and use them to develop theories

 Tool: Language of mathematics (a bridge between theory and experiment)

 Classical physics: includes the principles of classical mechanics, thermodynamics, optics, and electromagnetism developed before

1900 (Newton mechanics)

 Modern physics: a major revolution in physics began near the end

of the 19th century (theories of relativity and quantum mechanics)

1.1 Standards of length, mass and time

In 1960, an international committee established a set of standards for the fundamental quantities of science call SI (Système International)

Length

 The distance between two points in space

 Standard in SI: meter (m)

 1960: 1m = the length of the meter was defined as the distance between two lines on a specific platinum–iridium bar stored under controlled conditions in France

 1960s-1970s: 1m = 1 650 763.73 wavelengths 1 of orange-red light emitted from a krypton-86 lamp

 1983: 1m = the distance traveled by light in vacuum during a time

of 1/299792458 second

1.1 Standards of length, mass and time

Mass

Standard in SI: kilogram (kg)

 1987: 1kg = the mass of a specific platinum–

iridium alloy cylinder kept at the International

Bureau of Weights and Measures at Sèvres,

France

Time

Standard in SI: second (s)

 1967: 1s = 9 192 631 770 times the period of

vibration of radiation from the cesium-133 atom

(in an atomic clock)

• [f ] = g([x ], [y ], [z ])

• Example:

• The dimensions of speedv = l/t are written [v ] = L/T.

• The dimensions of area A = l × l are [A ] = L × L = L2.

Example 1.1 Analysis of an equation

Show that the expression , where represents speed, acceleration, and an instant of time, is dimensionally correct.

• Solve:

• The dimensions of v: [v] = L/T

• The dimensions of at: [at] =

have the same dimensions on both sides

•  

1.4 Estimates and Order-of-Magnitude

+ The same rule holds for numbers less than 1 Ex: (2 SF), (4 SF)

•  

1.5 Significant figures

The rule of determinating the number of significant figures

When multiplying several quantities, the number of significant figures in the final answer is the same as the number of significant figures in the quantity having the smallest number of significant figures The same rule applies to division

Ex: Report the result of multiplications

 The area of a carpet whose length is 15.24 m and whose width is 2.19 m

 The area of the disc whose radius is 6.0 cm

•  

1.5 Significant figures

The rule of determinating the number of significant figures

When numbers are added or subtracted, the number of decimal places in the result should equal the smallest number of decimal places of any term in the sum or difference

Ex:

Note: The rule for rounding number

 The last digit retained is increased by 1 if the last digit dropped is greater than 5 (Ex: 2.567 2.57)

 If the last digit dropped is less than 5, the last digit retained remains as

it is (Ex: 2.564 2.56)

 If the last digit dropped is equal to 5, the remaining digit should be rounded to the nearest even number (Ex: 2.565 2.56, 2.555 2.56)

•  

Kinematics : describe the motion of an object while ignoring the interactions with external agents

 Motion in one dimension: motion of an object along a straight line

 Particle model: describe the moving object as a particle regardless

of its size (a particle to be a point-like object)

Physical terms

http://www.conservapedia.com/Physical_Science_Terms

motion, particle, kinematics, position, reference point, coordinate system, velocity, speed, average/instantaneous velocity/speed, derivative, acceleration, gravity, resistance, period, angular speed, centripetal acceleration, tangential and radial acceleration, relative velocity/acceleration

2.1 Position, velocity, speed

Position

A particle’s position is the location of the particle with respect to

a chosen reference point that we can consider to be the origin of a

2.1 Position, velocity, speed

Displacement and distance

The displacement of a particle is its change in position in some

time interval

As the particle moves from an initial position to a final position , its displacement is given by

Note: Displacement differs from distance

Ex: After each period of motion of a particle moving in a circle of radius :

2.1 Position, velocity and speed

Velocity and speed

The average velocity of a particle is defined as the particle’s displacement divided by the time interval during which that displacement occurs:

Dimension: L/T

Note 1: In one dimension motion, the average velocity can be positive or negative, depending on the sign of the displacement

Note 2: Velocity differs from speed

The average speed of a particle is defined as

•  

2.2 Instantaneous velocity and speed

Instantaneous velocity

The instantaneous velocity (or velocity for short) of a particle at a particular instant in time equals the limiting value of the ratio as approaches zero:

Note 1: The instantaneous velocity can be positive, negative, or zero

Note 2: Velocity differs from speed

The instantaneous speed (or speed for short) of a particle is defined as the magnitude of its velocity

•  

2.3 Particle under constant velocity

Two basic steps to solve a problem:

 Identify the analysis model that is appropriate for the problem

 The model tells you which equation(s) to use for the mathematical representation

2.3 Particle under constant velocity

Analysis model: particle under constant velocity

If the velocity of a particle is constant, its instantaneous velocity

at any instant during a time interval is the same as the average velocity over the interval:

The position of the particle as a function of time is given by

Note: Particle under constant speed

If a particle moves at a constant speed through a distance along a straight line or a curved path in a time interval , its constant speed is

•  

2.4 Acceleration

Average acceleration

The average acceleration of the particle is defined as the change

in velocity divided by the time interval during which that change occurs:

•  

Acceleration is a vectorial quantity

Note: For the case of motion in a straight line

 When the object’s velocity and acceleration are in the same direction, the object is speeding up

 when the object’s velocity and acceleration are in opposite directions, the object is slowing down

•  

2.5 Particle under constant acceleration

Analysis model : Particle under constant acceleration

If a particle begins from position and initial velocity and moves

in a straight line with a constant acceleration , its subsequent position and velocity are described by the following kinematic equations:

•  

EX2-1 In a 100m foot-race, you cover the first 50m with an average velocity of 10m/s and the second 50m with an average velocity of 8m/s What is your average velocity for the entire 100m.

• EX2-2 A car travels 80km in a straight line If the first 40km is covered with an average velocity of 80km/h, and the total trip takes 1,2h, what was the average velocity during the second 40km?

• EX2-3 You run 100m in 12s, then turn around and jog 50m back toward the starting point in 30s Calculate your average speed and your average velocity for the total trip.

• EX2-4 Two train 75 km apart approach each other on parallel tracks, each moving at 15km/h A bird flies back and forth between the trains at 20km/h until the trains pass each other How far does the bird fly?

2.6 Freely falling object

A freely falling object is any object moving freely under the influence of gravity alone, regardless of its initial motion

If we neglect air resistance and assume the free-fall acceleration does not vary with altitude over short vertical distances, the motion of a freely falling object moving vertically is equivalent to the motion of a particle under constant acceleration in one dimension

apply the particle under constant acceleration model ()

2.6 Freely falling object

EX 2.5 A stone thrown from the top of a

building is given an initial velocity of 20.0

m/s straight upward The stone is launched

50.0 m above the ground, and the stone just

misses the edge of the roof on its way down

(a) Using as the time the stone leaves the

thrower’s hand at position A, determine

the time at which the stone reaches its

maximum height

(b) Find the maximum height of the stone

(c) Determine the velocity of the stone when

it returns to the height from which it was

thrown

(d) Find the velocity and position of the stone

at s

•  

2.6 Freely falling object

• EX2-6 Upon graduation, a student

throws his cap upward with an initial

speed of 14,7m/s Given that its

acceleration is 9,8m/s2 downward

(we neglect air resistance)

• a) How long does it take to reach its

2.6 Freely falling object

• EX2-7 On a highway at night you see a stalled vehicle and brake your

car to stop with an acceleration of magnitude 5m/s2 (deceleration) What is the car’s stopping distance if its initial speed is

• a) 15 m/s (about 54 km/h)

• b) 30 m/s 

• E2-8 An electron in a cathode-ray tube accelerates from rest with a

constant acceleration of 5,33 1012 m/s2 for 0,15 s The electron then drifts with constant velocity for 0,2 m Finally, it comes to rest with

an acceleration of -0,67 1043 m/s2 How far does the electron travel ?

2.6 Freely falling object

EX2-8 While standing in an elevator, you see a screw fall

from the ceiling The ceiling is 3m above the floor.

a) If the elevator is moving upward with a constant speed of 2,2m/s, how long does it take for the screw to hit the floor?

b) How long is the screw in the air if the elevator starts from rest when the screw falls, and moves upward with a constant acceleration of a = 4m/s2 ?

3

3.1 Position, velocity, acceleration vectors

Position vector : drawn from the origin of

some coordinate system to the location of

the particle in the plane

Displacment vector:

•  

Average velocity vector during :

Instantaneous velocity:

3.1 Position, velocity, acceleration vectors

Average acceleration is the change in its instantaneous velocity vector divided by the time interval during which that change occurs

3.2 Two-dimensional motion with

 the position vector:

 the velocity vector:

 the acceleration vector:

where and are the unit vectors of and axes, respectively

•  

3.2 Two-dimensional motion with

In the case of constant acceleration, , its components and also are constants Therefore, we can model the particle as a particle under constant acceleration independently in each of the two directions

•  

3.2 Two-dimensional motion with

Example 3.1 A particle moves in the plane, starting from the origin at with an initial velocity having an component of 20 m/s and a component of 15 m/s The particle experiences an acceleration in the direction, given by

(a) Determine the total velocity vector at any time.

(b) Calculate the velocity and speed of the particle at s and the

angle the velocity vector makes with the axis.

(c) Determine the and coordinates of the particle at any time

and its position vector at this time.

•