Speedand

Velocity

Distance vs. Displacement

• You drive the path, and your odometer goes up by 8 miles (your distance).

• Your displacement is the shorter directed distance from start to stop (yellow arrow).

• What if you drove in a circle?start

stop

Speed

• Speed is distance / time

or more accurately

t

dv

t

dv

Time

• What is time?

Constant speed

• A moving object that doesn’t change it’s speed travels at constant speed

• Constant speed means equal distances are covered in an equal amount of time

Constant speed

Distance in cmPosition

• Shown as a series of dots (center of mass image)

1

4

3 4

5 6

7 8 9 10

11

12

Time in seconds

2 5 6

What is the speed?

Constant speed

• Shown as a graph

Time

Posi

tion

3 4 52

2

4

6

8

1

What is the speed of this object?

Calculating Speed

• Speed = Distance Time

• If a runner travels 100 m in 10 seconds what was his average speed?

• Probably not constant• Can solve for the other pieces too• Distance = speed x time• Time = Distance

Speed

Speed is a scalar quantity

• What is it missing?

• instantaneous velocity - the velocity that something has at any one instance

– (The terms instantaneous speed and avg. speed may also be used)

interval timentdisplaceme = velocity average

t

dv

_

The average velocity for a trip might be 53

miles/hour.

However, during this trip your instantaneous

speed might have been 0 miles/hour at a stoplight or 70

miles/hour on the open road.

Show All Work Including The EquationS and Units

SAWITESU

An object is goes 30m North in 13 seconds. What is its velocity?

SAWITESU

Key Concepts

t

dv Speed =

Velocity is a vector quantity: Speed and direction