Lab 1.1 MEASURING VELOCITY
BACKGROUND:
Both speed and velocity measurea rate of motion. Motion involves a change in position compared to a stationary reference point. In order to measure the rate of motion both the change in position and time must be considered. For example, think about a sprinter running the 100-meter dash in the Olympics. The sprinter’s change in position is 100.0 meters from the start line. The sprinter’s running time is measured electronically to 1/1000 second. After measuring distance and time, speed is calculated by dividing distance by time. See the mathematical equation below.
or
For example, the sprinter’s speed would be calculated by dividing the distance of 100.0 meters by the time of 11.795 seconds, as shown below.
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So, the runner’s speed would be 8.48 meters per second or 8.48 m/s.
In this lab your task is to measure distance and time in order to calculate speed. Three different bubble tubes will be used. You will determine the speed of the bubble as it moves up each colored tube.
PURPOSE: To investigate the mathematics of speed.
PRE-LAB QUESTIONS:
1. What two pieces of information would you need if you wanted to know the speed of a train traveling from San Francisco to Los Angeles?
2. a. Mathematically, what would you do with the two pieces of information in order to calculate the speed of the train?
b. Write a mathematical equation that shows how to calculate speed.
3. a. To find the speed of the bubble as it moves up the tube, what do we need to measure?
b. What measuring tools will be needed in order to find the speed of the bubbles in the tubes?
4. Measurements must be recorded with a proper unit, since “naked numbers” are not allowed.
a. In the example in the background, the unit of distance in the race was meters. Will meters be an appropriate unit of measurement in today’s lab? Why or why not?
b. A student measures the length of the bubble tube and records it as “35.8”. What unit needs to be written after this number? Give both the name and the abbreviation of the correct unit of distance.
c. What will be the correct unit for time?
PROCEDURES: Read all of the procedures before beginning.
- Copy the data table below to organize the data you collect. Use a straight edge to draw the lines.
Data Table: Speed of the Bubble Tubes
Bubble Tube / Distance(cm) / Time(s) / Speed (cm/s)D ÷ T
Green / Long
Medium
Short
Red / Long
Medium
Short
Blue / Long
Medium
Short
B. Obtain one colored tube. The masking tape represents the starting line. Three other lines have been marked on the tube with a black pen.
C. Measure the distance from the start line (bottom edge of the masking tape) to the third black line marked above the masking tape. This is the “long” distance. Record the measurement to the nearest 0.1(one-tenth) of a centimeter in your data table (e.g.: 14.8 cm). Each measurement recorded should have units.
D. Measure the distance from the masking tape to the second black line. This is the “medium” distance. Record the measurement to the nearest 0.1 (one-tenth) of a centimeter in your data table.
E. Measure the distance from the masking tape to the first black line. This is the “short” distance. Record the measurement to the nearest 0.1 (one-tenth) of a centimeter in your data table.
F. Measure the time it takes the bubble to travel the longest distance.
- After flipping the tube, start timing when the top of the bubble reaches the starting line (bottom edge of masking tape). Stop timing when the top of the bubble reaches the third black mark.
- Practice timing two or three times, until the times are consistent (close to the same).
- After practicing, measure and record the time to the nearest .01 (one hundredth) of a second in your data table.
Stopwatch reads Record time as 2.15 seconds
- Remember, each measurement recorded in the table should have units (e.g. 2.15 s).
G. Repeat procedure F for the medium distance. Record this in the data table.
H. Repeat procedure F for the short distance. Record this in the data table.
I. Repeat procedures B-H for the two other colored tubes.
J. For each color and distance, calculate the speed of the bubble. Hint: review your pre-lab questions if you are unsure about how to calculate speed. Record your answers in the data table. Don’t forget units!
K. Set up the graph you will plot your data on.
1 / 2- Arrange the paper so that the y-axis (vertical axis) will be the long side of the paper.
- Write“distance (cm)” to the left of the y-axis (vertical axis)
- Write “time (s)” just below the x-axis (horizontal axis).
- The origin (0,0) is where the two axes cross. Label the x-axis as follows. Go two lines over from zero and mark “1”. Continue labeling every other line to the edge of the paper. Refer to the diagram at right to see how to scale and label each axis.
- On the y-axis, label every line. Refer to the diagram at right.
L. Graph the data for the green colored tube.
- On the x-axis, find the time measured for the bubble to travel the long distance.
- On the y-axis, find the measured value for the long distance.
- Go up from the x-axis and right from the y-axis and draw a dot where the two imaginary lines would meet. This is a data point.
- Plot two more data points, one for the medium distance and one for the short distance.
- The three data points should fall on an approximately straight line. Draw a “best fit” line.
- Rather than “connect the dots”, in science we often draw a “best fit line”. It is the line that comes closest to all of the data points but may not go directly through each point.
- Label the line “green”.
M. Plot 3 data points for the red tube and draw a “best fit” line. Label the line “red”.
N. Plot 3 data points and draw a “best fit” line for the blue tube. Label the line.
INTERPRETATIONS:
1. a. Compare the speed of the bubbles in each tube. Which color had the fastest bubble?
Which color had the slowest bubble?
b. Refer to your graph. How does the steepness of the red bubble tube line compare to the steepness of the green bubble tube line?
c. Copy and complete the following sentence. “The steeper the line, the ______the speed.”
2. a. Create a chart to compare the amount of time it would take for the bubble to travel 25 cm in the red tube and the green tube. Use your graph to find this information. Hint: find 25cm on the y-axis and go over to the line and down to find time on the x-axis.
Tube / Time to Travel 25 cm / Relative Speed (fastest or slowest?)red
green
b. Based upon the chart comparing travel times for the same distance, copy and complete the following sentence. The greater an object’s speed, the ____ (less or more) time it takes to travel the same distance. So speed and time are ____ (directly or inversely) related.
*Note: In a “direct” relationship, increasing one variable causes the other variable to increase. In an “inverse” relationship, increasing one variables causes the other variable to decrease.
3. a. Create a chart to compare the distance the bubbles travel in 5 seconds. Use your graph to find this information.
Tube / Distance Traveled in 5 seconds / Relative Speed (fastest or slowest?)red
green
b. Based upon the chart comparing distances traveled in the same time, copy and complete the following sentence: The greater an object’s speed, the ____ (less or more) distance it travels in the same time. So speed and distance are ____ (directly or inversely) related.
4. Remember that the speed equation is
a. Copy and complete the following sentence: Distance is the ___ (numerator or denominator) of the speed ratio and distance and speed are ____ (directly or inversely) related. If you increase distance traveled but keep time the same, the speed gets ___ (larger or smaller).
b. Copy and complete the following sentence: Time is the ___ (numerator or denominator) of the speed ratio and time and speed are ____ (directly or inversely) related. If you increase time of travel but keep distance the same, the speed gets ___ (larger or smaller).
Refer to the graph at right for questions #5-9.
5. Which object has the greatest speed? How do you know?
6. Which object would take the longest time to travel 15 cm?
7. Which object would go farthest in 20 seconds?
8. How far would object A go in 10 seconds?
9. How much time would it take object C to go 10 cm?
CONCLUSION:
Part 1: In three to four sentences, describe how you would measure the speed of a skateboarder as he rides to the mall.
Part 2: Copy the axes below (no numbers needed). Sketch two lines on the graph, one for a skateboarder and one for a teenager riding a bicycle. Label each line. Write one sentence to explain why you drew the lines the way you did.
IPS/GS Lab Manual version 3.110/14/18Unit 1 page 1