International University,
Vietnam National University, HCMC
Physics 1: Mechanics
Tran Nguyen Lan, Ph.D
Department of Physics, HCMIU-VNU
Phone: 0905 623 462, email: lantrann@gmail.com
Room: A.503
Week 01
• Class rule:
– Not using phones and computers for any purposes
other learning. If any student breaks the rule, the
whole class is not allowed to use phones and
computers!
– I’ll check your attendance regularly. If you are
absent for three times, you are not allowed to
take exams!
– No chatting, texting in the class. If you have an
urgent call, go out to take it. Otherwise, you must
cancel the call!
https://drive.google.com/file/d/1aSR7PEIH6kfWQApoPtP8k4xLH_i6A8VA/view?usp=sharing
• No of credits: 02 (30 teaching hours)
• Textbook: Halliday/Resnick/Walker (2011) entitled
Fundamentals of Physics, 9th edition, John Willey &
Sons, Inc.
Course Requirements
• Attendance + Discussion + Homework: 15%
• Assignment: 15%
• Mid-term exam: 30%
• Final: 40%
Preparation for each class
• Read text ahead of time
• Finish homework
Content
Part A Dynamics of Mass Point
- Chapter 1 Bases of Kinematics
- Chapter 2 Force and Motion (Newton’s Laws)
Midterm exam
Part B Laws of Conservation
- Chapter 3 Work and Mechanical Energy
- Chapter 4 Linear Momentum and Collisions
Part C Dynamics and Statics of Rigid Body
- Chapter 5 Rotation of a Rigid Body About a Fixed Axis
- Chapter 6 Equilibrium and Elasticity
- Chapter 7 Gravitation
Final exam
Chapter 1 Bases of Kinematics
1. 1. Motion in One Dimension
1.1.1. Position, Velocity, and Acceleration
1.1.2. One-Dimensional Motion with Constant Acceleration
1.1.3. Freely Falling Objects
1. 2. Motion in Two Dimensions
1.2.1. The Position, Velocity, and Acceleration Vectors
1.2.2. Two-Dimensional Motion with Constant
Acceleration. Projectile Motion
1.2.3. Circular Motion. Tangential and Radial Acceleration
1.2.4. Relative Velocity and Relative Acceleration
Measurement
• Why do we need physics?
– Explain the nature (develop modern technologies!)
• How to know the laws of physics are correct?
– Do experiment
• Physical quantities have their own units
Quantities
length
mass
time
SI system
meter (m)
kilogram (kg)
second (s)
CGS system
centimeter (cm)
gram (g)
second (s)
1.1. Motion in one dimension
• Dynamics and kinematics:
– Kinematics: describing motion (how objects move)
– Dynamics: concerning causes of motion (why objects
move)
• Two basis quantities of motion:
– Displacement: Δx = xf – xi
– Time interval: Δt = tf – ti
• Restriction for this chapter:
Xf
(t = tf)
Xi
(t = ti)
– Along the straight line only (vertical, horizontal, slanted)
– Will not discuss the cause of motion (force)
– Consider particles or particle-like objects only
A. Position: determined in
A. Position: determined in
a reference frame
A. Position,
velocity,
and
acceleration
a reference frame
Space vs. time graph
Position
defined in terms of a frame of reference.
Space vs. time graph
t=0 s: x=-5 m
t=3 s: x=0 m
t=0 s: m
x=-5 m
Dx=0-(-5)=5
t=3 s: x=0 m
Dx=0-(-5)=5
m
Two features
of displacement:
- its direction (a vector)
- its Two
magnitude
features of displac
Motion of an armadillo
- its direction (a vecto
For positive
- its direction:
magnitudeΔx > 0
For opposite direction: Δx < 0
Question
t0 = 0
x0 = 0
(origin)
t1 = 1 h
t2 = 1.5 h
x1 = 40 km
x2 = 20 km
(a) What is the displacement of the car after 1.5 h?
(b) What is the distance the car travelled after 1.5 h?
x
x
Position-time graph
Note: position-time graph is not necessarily a straight line,
even though the motion is along one dimension!
B.1. Average velocity:
A.
Position,
velocity,
and
acceleration
Δx x - x
an object moves)
vavg =
= 2 1
Average velocity - Unit: m/s, km/h, or cm/s
Δt t 2 - t1
B.1. Average velocity:
- Magnitude: the
slope
straight
Unit:
m/s of
or the
cm/s
Δx x 2 - x1
line that connects
two particular
vavg =
=
The navg of the armadillo:
Δt t 2 - t1
points on the x(t) curve.
- Sign: the sign of Δx 6m
Unit: m/s or cm/s
v avg =
= 2m/s
3s
The navg of the armadillo:
=
v avg
6m
3s
= 2m/s
speed
B.2.Average
Average speed:
s avg
total distance
=
Δt
Note: average speed does not include direction
B.2. Average speed:
s avg =
total distance
Note: average speed does
not include direction
Question
t0 = 0
x0 = 0
(origin)
t1 = 1 h
t2 = 1.5 h
x1 = 40 km
x2 = 20 km
What is
(a) the average velocity
(b) the average speed
of the car during the total trip of 60 km?
x
x
Instantaneous velocity
Average vs Instantaneous Velocity
The instantaneous velocity
corresponds to the velocity of
a particle at a particular time.
Average velocity
Instantaneous velocity
Speed (not average speed) is the magnitude of velocity: |v|
Constant velocity
position
v
velocity
v = const
- The instantaneous velocities
are always the same
- All the instantaneous velocities
will also equal the average
velocity
Sample Problem :
The position of an object described by:
x = 4-12t+3t2 (x: meters; t: seconds)
(1) What is its velocity at t =1 s?
v=dx/dt=-12+6t=-6 (m/s)
(2) Is it moving in the positive or negative direction of x
just then? negative
(3) What is its speed just then? S=6 (m/s)
(4) Is the speed increasing or decreasing just then?
0<t<2: decreasing; 2<t: increasing
(5) Is there ever an instant when the velocity is zero? If
so, give the time t; if not answer no. t=2 s
(6) Is there a time after t= 3 s when the object is moving
in the negative direction of x? if so, give t; if not,
answer no. no
Sample Problem :
The position of an object described by:
x = 4-12t+3t2 (x: meters; t: seconds)
(1) What is its velocity at t =1 s?
v=dx/dt=-12+6t=-6 (m/s)
(2) Is it moving in the positive or negative direction of x
just then? negative
(3) What is its speed just then? S=6 (m/s)
(4) Is the speed increasing or decreasing just then?
0<t<2: decreasing; 2<t: increasing
(5) Is there ever an instant when the velocity is zero? If
so, give the time t; if not answer no. t=2 s
(6) Is there a time after t= 3 s when the object is moving
in the negative direction of x? if so, give t; if not,
answer no. no
A. Position, velocity, and acceleration
Acceleration
When a particle’s velocity changes, the particle is said to
undergo acceleration
Average acceleration
Unit: m/s2
Instantaneous acceleration
1st derivative
2nd derivative
• Example
t = 10 s
speed = 40 m/s
t=0s
(1) speed = 0 m/s t = 0 s
x
(2)
speed = 40 m/s
speed = 0 m/s
What is the average acceleration in each case?
t = 40 s
x
• Example
t = 10 s
speed = 40 m/s
t=0s
(1) speed = 0 m/s t = 0 s
x
(2)
speed = 40 m/s
speed = 0 m/s
t = 40 s
What is the average acceleration in each case?
Note on the sign of acceleration: If the signs of the velocity and
acceleration of a particle are the same, the speed of the particle
increases. If the signs are opposite, the speed decreases.
x
Homework for 1.1
• Problems 4, 9 (page 32 in the text book)
• Problems 15, 17 (page 33)
• Problems 20, 22 (page 33)