Finding the average speed, using the timer to measure time and displacement.
INTRODUCTION - READ AND FILL THE BLANK FOR FULL CREDITS.
The recording timer is a device that helps you study motion. It consists of a simple electric vibrator through which paper tape can be drawn. A carbon paper disk placed between the vibrating arm and the paper tape leaves a mark on the tape each time the arm goes up and down. Last time you found that the time (or period) between 2 dots on the tape = _____ s.
In this lab, a trip of timer tape will be attached to a constant-velocity vehicle as shown below.
The movement of the attached tape through the timer equals the displacement of the moving________.
If the distance between 2 dots is large, the car was moving ___________; if the distance between the dots is small, the car was moving __________.
FOR THIS LAB, YOU WILL USE THE TIME REPRESENTED BY SIX SUCCESSIVE DOTS ON THE TIMER TAPE
AS ONE TIME INTERVAL. (5 full vibrations of the arm , or 5/60s.)
The speed will be measured in centimeters (distance covers by the car) per time interval. Then in centimeters per seconds.
MATERIAL
Recording timer, C-Clamp, time tape, carbon paper discs, vehicle battery powered
PROCEDURE
1. Assemble the apparatus as shown above
Insert 1.5 m of timer tape into the timer. Make sure the tape moves freely through the timer. Using a piece of masking tape, attach the timer tape to the constant-velocity vehicle. Place the vehicle into his track in aluminum.
2. start the timer. Then start the vehicle and allow it to pull the timer tape through the recording timer. Stop the vehicle and the timer after the tape has been pulled through the timer. Make sure you can see the dots and that the tape looks like the image above. If not, start over fixing the problem.
3. Write "start: at the end of the tape that was attached to the vehicle , as shown above. (the "0 "dot). Count off five spaces from the "0 "dot. Mark this dot "1". Count off five more dots from the dot marking interval 1 and label this dot "2 ". Continue counting 5 spaces and marking intervals 3, 4, 5, etc.. These numbers represent the intervals of time that elapsed as the vehicle traveled the distance between dot 0 and each fifth numbered dot.
4. beginning at the "0"dot, measure in centimeters the distance on the recording tape of the first interval (between dot 0 and dot 1). Record this distance in TABLE 1 (col2, row1) as the displacement during interval 1. Then measure the distance between dot "2 "and "3". Record in the TABLE 1 (col2, row2). Then the distance between "3"and "4" (col2, row3). and so forth.
5. The average velocity, for each time interval (5 spaces) is the displacement divided by one interval one time.
(V)av = displacement / time interval. Since the time for each interval is one interval ( t = 1 interval), the velocity will be numerically equal to the displacement during the interval. For example , a vehicle that traveled 3.5cm during the first interval will have an average velocity of 3.5cm/interval since 3.5/1 interval = 3.5cm/interval. Record each average velocity next to the corresponding time interval.
6. The total displacement of the vehicle at the end of any given interval is the sum of the displacements during each preceding interval plus the current measurement. The total displacement at the end of interval 1 is the the displacement during interval 1. The total displacement at the end of interval 2 is the sum of the displacement during interval1 plus the displacement during interval 2. The total displacement of each remaining interval is found in the same manner. Calculate the total displacement of the vehicle for each interval and record the values in table1.
| time (interval) | displacement (cm) | Average velocity (cm/interval) = previous column | total displacement (cm) |
| 1 | (between dot 0 and 1) ____________ | ______________ | ___________________ |
| 2 | (between dot 1 and 2) ______________ | __________ | _________ |
| 3 | ___________ | ___________ | __________ |
| 4 | _________ | __________ | _________ |
| 5 | ____________ | ___________ | _____________ |
| 6 | ___________ | __________ | _____________ |
| 7 | ___________ | ___________ | ___________ |
| 8 | ___________ | __________ | ________________ |
| 9 | ________ | _______ | ___________ |
| 10 | _________ | ____________ | _________ |
ANALYSIS (do not use your TI)
1) MAke a graph average velocity vs time. don't forget the title and everything else.
What do you notice ?
2) Make a graph total displacement vs time. Find the best fit line .
Find the slope. slope = ____cm/time interval. Is it close to the velocity found in 1 ) ? why ?
3) Find the average velocity for the whole motion. Vav = total displacement / time = _________ cm / time interval.
Is it close to what was found in 1 ) and 2)
4) Let's find the speed of the car. You know 1 time interval = 5 spaces = 5 (1/60 s ) = ________ s.
Divide the speed found in 2 ) (in cm/time interval) by the time in seconds. (above). speed = _____ cm/s
5) Get back to your graph velocity vs time
Find the total area under the graph. (the area of a triangle). Compare this area to the total displacement.
You will learn that total displacement = total area under graph velocity vs time.
_