Announcements:

• Questions about WebAssign?

• My office hours: M, W, F 1:00-2:00, Olin 215

• Labs start next week Bring ThinkPads to lab

TUTOR & HOMEWORK SESSIONS This year’s tutors: Jerry Kielbasa, Matt Rave, Christine Carlisle

 

All sessions will be in room 107 (next to lecture room).  

 Tutor sessions in semesters past were very successful and received high marks from students.

All students are encouraged to take advantage of this opportunity. 

Monday Tuesday Wednesday Thursday Friday Saturday Sunday

4-6 4-6 4-6  4-6    

6-8 6-8 6-8 6-8

• In this chapter we will only look at motion along a line (one dimension).

• Motion can be forward (positive displacement) or backwards (negative displacement)

Chapter 2: Motion in One Dimension

Reading assignment: Finish Chapter 2

Homework 2: (Due Wednesday, Aug 31)

(Chp 2): 3, 10, 12, 18, 41, 58

Remember: Homework 1 is due this Monday, Aug. 29.

Displacement and

total distance traveled

Displacement of a particle: Its change in ______________________:

12 xxx x2 final position

x1 initial position

Don’t confuse displacement with the _______________ distance traveled.

Example: Baseball player hitting a home run travels a total distance of 360 ft, but his displacement is 0 ft!!

Displacement is a ___________: It has both, magnitude and direction!!

Total distance traveled is a scalar: It has just a magnitude

Velocity and speed

Average ______________ of a particle:

12

12, tt

xx

t

xv xavg

x: displacement of particle

t: total time during which displacement occurred.

Average _________ of a particle:

Velocity is a vector: It has both, ___________ and _________!!

Speed is a scalar: It has just a _________________

timetotal

distance total _______________

The position of a car is measured every ten seconds relative to zero.

A) 30 m

B) 52 m

C) 38 m

D) 0 m

E) - 37 m

F) -53 m

Find the displacement, average velocity and average speed between positions A and F.

Blackboard example 2.1

Instantaneous velocity and instantaneous speed

dt

dx

t

xv

tx

0

lim

Instantaneous velocity is the _________ of x with respect to t, (dx/dt)

Velocity is the ________________ of a position-time graph!

The instantaneous speed (scalar) is defined as the magnitude of its velocity (vector)

Blackboard example 2.2

A particle moves along the x-axis. Its coordinate varies with time according to the expression x = -4t + 2t2. -4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5 4

dis

pla

cem

ent

(m)

time (s)

t

x

(a) Determine the displacement of the particle in the time intervals t=0 to t=1s and t=1s to t=3s.

(b) Calculate the average velocity during these two time interval.

(c) Find the instantaneous velocity of the particle at t=2.5s.

(d) Is the velocity constant or is it changing?

Acceleration

When the velocity of a particle (say a car) is changing, it is accelerating. (Decelerating/braking = ________________ acceleration).

12

12, tt

vv

t

va xxx

xavg

The average acceleration of the particle is defined as the change in velocity vx ________________ the time interval t during which that change occurred.

dt

dv

t

va xx

tx

0

lim

The instantaneous acceleration equals

the derivative of the velocity with respect to _________ (slope of a ______________________ graph).

Because vx = dx/dt, the acceleration

can also be written as:

????

Units: m/sec2

Find the appropriate acceleration graphs

parabola