POSITION, DISTANCE, & DISPLACEMENT

AVERAGE SPEED AND VELOCITY

INSTANTANEOUS VELOCITY

Lecture for 9/18/07

Position, Distance, and Displacement Set up a coordinate system

Right is usually positive, left is usually negative

Distance = total length of travel Displacement = change in position = final

position – initial position or ∆x = xf - xi

Displacement can be positive, negative, or zero

Position, Distance, and Displacement Cont.

What is your distance traveled if you start at your friend’s house travel to the grocery store then back to your house?

What is your displacement for the same route? What are some routes that you could take to

have a negative displacement? How about a displacement of zero?

Average Speed and Velocity

Average speed = distance/elapsed time

Average Speed and Velocity Con’t. Average velocity =

displacement/elapsed time Sign tells the direction of the object motion

+ sign means xf > xi

– sign means xf < xi

Graphical Interpretation of Average Velocity

Slope of a line connecting two points on an displacement vs. time plot is equal to the average velocity during that time interval

Complete 1-8 on Creating velocity versus time graphs WS

Instantaneous Velocity

Average velocity isn’t very descriptive about the exact rate of motion of an object at a specific time

Ideally you would calculate the average velocity for every minute or second

Instantaneous velocity, v = When the velocity is constant, average velocity

over any time interval = instantaneous velocity at any time

When the velocity changes, the instantaneous velocity at a given time is equal to the slope of the tangent line at that point on a displacement vs. time graph