My Favorite Physics Lab Report

Position and Velocity

By: Luci Keller

Partner: Wendy Loomis

9/3/15

Experimental Description:

During this experiment we completed four different tasks to analyze position and velocity. First we dropped one bean bag every second while someone walked at a steady pace so we could use the distances between the bags to analyze velocity. Then we took turns walking forwards/backwards going fast/slow in front of a sonic range motion sensor, creating graphs of our positions and velocities vs time. We combined the bean bag method with the motion sensor method to compare our bean bag speed calculations vs the calculations from the graphs produced. We did this by dropping one bean bag per second as someone walked towards the motion sensor. Finally, we matched position and velocity to a given graph by determining how we could move in front of the motion sensor to best replicate the velocity on the given graph.

Data and Analysis:

TASK 1: Below is a sketch that replicates the dropping of bean bags while a person walked at two different speeds.

 

From the bean bag positions for both walks, you can tell that the person was walking at a steady pace because the distance between each bean bag is close to the same over a time interval of one second. Each walk lasted 4 seconds. You can tell that the person was walking faster in the first walk because they traveled a much larger distance than the second walk in the same amount of time.

Task 2: We then created different position vs time and different velocity vs time graphs using the sonic range motion sensor.

Position graph 1

                                                                  Position graph 2 

The sign (positive/negative) of the slope (Δd/Δt) graphs tells you the direction that the person was moving. In position graph 1, the person was moving backwards because their position is increasing with time (positive slope), meaning they are moving away from the sensor. In position graph 2, the person was moving forward because their position was decreasing with time (negative slope), meaning they are moving towards the sensor. The size of the slope tells you fast the person was walking. A larger slope means that the person was walking faster, and a smaller slope means they were walking slower.

Velocity graph 1

Velocity graph 2 

The sign (positive/negative) of the velocity tells you the direction the person was walking. In velocity graph 1, the person was gaining distance (equivalent to walking away from the motion sensor) because the velocity is positive. In velocity graph 2, the person was decreasing in distance (equivalent to walking towards the motion sensor) because the velocity is negative. The absolute value of the size of the velocity tells you how fast the person was walking. In velocity graph 1, just by looking at the graph, it appears that the average velocity was .3 m/s. In velocity graph 2 it was about .5 m/s (absolute value of -.5 m/s), meaning that the person is velocity graph 2 was walking faster.

Task 3:

Graphs that correspond with bean bags

 

We calculated the speed of the walker using the bean bags first by finding the mean of the distances between each of the bean bags and dividing that by the total seconds traveled.

.69m + .65m +.61m + .59m + .62m / 5 sec = .63 m/s

From the velocity graph, we can see that the walker’s actual speed was around .40 m/s. Our calculations of speed using the bean bags was around .23 m/s faster than the actual speed, meaning our results were not very reliable.  

Task 4:

Recreation of given velocity graph

From looking at the given graph, we determined that we needed to stand still for the first two seconds, walk backwards (away from the motion sensor) for two seconds, stand still for one second, walk forwards (toward the motion detector) for 3 seconds, then stop for the rest of the time. The above graph was created by following these steps, and is fairly close to the original graph.

Conclusion:

To conclude, the relation between position and velocity and time can be analyzed through graphs. We determined that a positive velocity means an object is gaining distance while a negative velocity means an object is decreasing in distance. A positive slope on a position graph means that the object is moving away from the motion sensor and a negative slope means that the object is moving towards the motion sensor. Errors that could have had effect on this experiment would be not correctly calibrating the motion sensor or not pointing the motion sensor at a flat moving object (i.e. a baggy wrinkly shirt could have caused errors in the measurement of position).