Wednesday, August 27

MotionPosition and Time

VelocityScientific Notation

Vectors

What is the difference between speed and velocity?

1. Speed is an average quantity while velocity is not.

2. Velocity contains information about the direction of motion while speed does not.

3. Speed is measured in mph, while velocity is measured in m/s.

4. The concept of speed applies only to objects that are neither speeding up nor slowing down, while velocity applies to every kind of motion.

1.What is the difference between speed and velocity?

B.Velocity contains information about the direction of motion while speed does not.

We will consider one dimensional motion at first.

Answer

Slide 1-3

One dimension

• In one dimension, velocity is either positive or negative. Speed is the magnitude of the velocity, so it is always positive.

A simplifying model in which we treat the object as if all its mass were concentrated at a single point. This model helps us concentrate on the overall motion of the object.

The Particle Model

Slide 1-13

Displacement

The change in the position of an object as it moves from initial position xi to final position xf is its displacement ∆x = xf – xi.

Slide 1-15

The position of an object is located along a coordinate system.

Position and Time

At each time t, the object is at some particular position. We are free to choose the origin of time (i.e., when t = 0).

Slide 1-14

Maria is at position x = 23 m. She then undergoes a displacement ∆x = –50 m. What is her final position?

–27 m –50 m

23 m 73 m

25% 25%25%25%1. –27 m

2. –50 m

3. 23 m

4. 73 m

• Maria is at position x = 23 m. She then undergoes a displacement ∆x = –50 m. What is her final position?

A. –27 m

Answer

Two runners jog along a track. The positions are shown at 1 s time intervals. Which runner is

moving faster?

A B

50%50%1. A2. B

Speed

Slide 1-22

The car moves 40 m in 1 s. Its speed is = 40 .

40 m

1 s

m

s

The bike moves 20 m in 1 s. Its speed is = 20 .20 m1 s

ms

Speed

Slide 1-22

The car moves 40 m in 1 s. Its speed is = 40 m

1 s = 40

m

s

The bike moves 20 m in 1 s. Its speed is = 20 .20 m1 s

ms

Velocity

Slide 1-23

Before considering vectors, a look at scientific notation and significant figures.

Note first lab next week will deal with how errors in measurements affect quantities calculated from those measurements.

Significant figures

Multiplying two numbers:

Adding two numbers:

Slide 1-24

Scientific Notation

Slide 1-25

Scientific Notation (continued)

Slide 1-26

Unit Conversions

Slide 1-27

Homework

• Reading Chapter 1:1-5• Problems Chapter 1: CQ3, CQ4, CQ6, MC21, 3,

4• DUE FRIDAY

– Reading Chapter 1: 5-7 VECTORS– Problems Chapter 1: MC24, MC28, 9, 10, 25, 36,

37, 38, WB 1.6 (27,28)