1

Constant & Changing Motion

2

Reference PointA fixed point from which direction is defined.The reference point can be anything.

PositionWhere something is, relative to the reference point.

Scalar and Vector• Scalar- has an amount or magnitude. It

is always postive

• Vector- has magnitude and direction. Can be positive or negative

3

4

Distance

The length traveled measured from start to finish.Scalar quantity. Has magnitude only

Use meters!!!

5

Example #1

A car drives 4 meters north, 3 meters south, then 5 meters north. What’s its total distance driven?

D = 4m + 3m + 5m

D = 12m

6

Displacement

The net difference between the starting point and the ending point.

d = dfinal – dinitial

7

Example #2

A car drives 4 meters north, 3 meters south then 5 meters north. What’s its displacement?

Δd = 9m north – 3m south

Δd = 6m north !

8

Speed

Total distance traveled divided by the total time elapsed. Speed represents the magnitude of velocity (scalar quantity) speed = distance/time•Speed is the absolute valueabsolute value of velocity.

• It is always a positivepositive value.•SpeedSpeed is the magnitude of velocity.

9

Average Velocity ( Vavg)

Velocity is a vector quantity (magnitude & direction)

Total distance traveled divided by the total time elapsed.

Vavg = d/t Units: m/s

10

Average Velocity

1 mile 2 miles 2 miles3 seconds1 second 2 minutes

home DairyQueen4 hr.

EXXON3 hr.

5 miles

Δt includes ALL time, whether you were moving or not!

Δt = 1 sec + 14400 sec + 120 sec + 10800 sec + 3 sec

Δt = 25324 sec (x 1 hr / 3600 sec = 7.03 hr)

Vavg = 5 mi / 7.03 hr

Vavg = 0.71 mi/hr

LHS

11

Instantaneous Velocity (V)

•Velocity at one point

•Δd and Δt are very, very, very, very……small!

12

Constant Velocity•If a body is moving at a constant velocity, the velocity never changes between intervals.•Doesn’t happen often in real life!•Ex:

V = 10 m/s V = 10 m/s V = 10 m/s

13

Acceleration•Acceleration is the change in velocity over time.•Average acceleration (aavg ) = change in velocity

time spent•aavg = ΔV / Δt

•Units: (m/s) ms s2

14

Acceleration Example #1•Find aavg.

Vi = 10 m/s Vf = 40 m/s

aavg = 40 – 10 m/s

2 s

*This means that the object’s velocity increases 15m/s every

second!

aavg = 15 m/s2

Δt = 2 sec

15

Acceleration Example #2•Find aavg.

Vi = 40 m/s Vf = 10 m/s

aavg = 10 – 40 m/s

2 s

*This means that the object’s velocity decreases 15m/s every

second!

aavg = -15 m/s2

Δt = 2 sec

16

Acceleration Example #3•Find aavg.

Vi = 40 m/s Vf = 40 m/s

aavg = 40 – 40 m/s

2 s

*This means that the object’s velocity is constant!

aavg = 0 m/s2

Δt = 2 sec

17

Four Basic Equations of Physics

• Conditions:– One-dimensional motion– Constant acceleration

18

Four Basic Equations of Physics•Vf = Vi + at

•d = Vi t + ½ at2

•2ad = Vf2 – Vi

2

• Vf + Vi 2d =

t