# Really confused need help on graphical determinations of speed vs. time data

1. Jul 5, 2004

### terpsgirl

I'm taking physics as a summer course and am having trouble on 3 questions in my pre-lab. I can't really explain...

1) Why is a graphical determination of the avg velocity obtained from the slope of a best-fit line drawn for the data more accurate than simply dividing the total distance by the total time?

I said it's more accurate because it shows you visually the data points and the spread.

2) WHy is a graphical determination of the avg velocity obtained from the slope of a best-fit line drawn for the data more accurate than calculating several velocities over small time intervals and averaging them together?Not sure?

3) Why is it more accurate to use the UGRAFIT Graphing Program to graphy, draw and determine the slpe of the best-fit line than to do the same by hand on a piece of graphy paper?

I said because sometimes when you end up w/ a lot of data it is more convienient and faster to do the data through the program because it comes out cleaner and saves time.

2. Jul 6, 2004

### JohnDubYa

1) Why is a graphical determination of the avg velocity obtained from the slope of a best-fit line drawn for the data more accurate than simply dividing the total distance by the total time?

It isn't.

2) WHy is a graphical determination of the avg velocity obtained from the slope of a best-fit line drawn for the data more accurate than calculating several velocities over small time intervals and averaging them together?

It isn't, if you average enough velocities.

3) Why is it more accurate to use the UGRAFIT Graphing Program to graphy, draw and determine the slpe of the best-fit line than to do the same by hand on a piece of graphy paper?

LOL! Your instructor's third question completely contradicts his first, since the graphing program divides the total distance by the total time. (Although it shows you a picture of a slope, it doesn't actually physically measure the sides of the slope triangle like you would when doing them by hand.)

3. Jul 6, 2004

Why?