Up and Down Labortatory

Up and Down Laboratory Materials: Motion Detector, Graphical Analysis Software, object to toss Goal: To determine the acceleration of gravity and examine the motion of an object in free fall Title/Introduction Try out the motion detector and answer the following questions: In what directions does the motion detector read motion? The motion detector reads motion in the up and down direction. How does the motion detector know how far away an object is? The motion detector sends off an ultrasonic wave that bounces off the object and is focused back into the motion detector and reads into a microphone that is translated into a graph. The microphone records how long it takes for a wave to bounce off an agent and translates its displacement. When an object moves toward the detector, does it read as a positive or negative velocity? When an object moves toward the detector the velocity is negative. When an object moves away from the detector the velocity is positive. Data Collection Hit collect on the data collection software. Toss the object into the air above the motion detector, starting about 30 cm away from it. Catch it when it gets back down to the same height. Try not to get your hands in the way of the object, redo if you see any spikes during the time the object was in the air. Look at the graph of position. Select the portion of the graph that the ball was in the air for, and zoom in for that time. Copy your screen and paste the graph below: Look at the graph of velocity. Select the portion of the graph that the ball was in the air for, and zoom in for that time. Copy your screen and paste the graph below: Look at the graph of acceleration. Select the portion of the graph that the ball was in the air for, and zoom in for that time. Copy your screen and paste the graph below: Graphing Take a look at the graph of velocity vs. time. You should be able to see a downward sloping straight line when the ball was in the air. Select only the portions of the graph that are part of that straight line and go to the graph options in the bottom corner. Apply a linear curve fit to the line. Copy your screen with the linear curve fit showing below: Take a look at the graph of acceleration vs. time. You should be able to see a mostly horizontal straight line when the ball was in the air. Select only the portions of the graph that are part of that straight line and go to the graph options in the bottom corner. Apply a linear curve fit to the line. Copy your screen with the linear curve fit showing below: Analysis What does the slope of the linear curve fit of velocity represent? The slope of the velocity graph represents the acceleration when it is in free fall, which is g or -9.8 m/s^2 What is the value and units of the slope? m= -9.073 m/s^2 The expected result for the slope is 9.8 m/s^2. Determine the percent error between this theoretical value and the experimental value you calculated. Apply any necessary unit conversions. Percent Error = {|Theoretical - Experimental| / Theoretical} * 100 Percent error= 8.01% What does the slope of the linear curve fit of acceleration represent? It represents the change in acceleration. What is the “r” value of the linear curve fit of acceleration? A good fit would be over 0.8, is yours a good fit? Our “r” value is 0.92; our value is a good fit. An “r” value is a scale between one and negative one; when the number is closer to one, it is good. Questions Using the graphs in your data section, determine when the ball was at its highest point. How did you know? The ball is at its highest point when the graph is at its lowest point because it would make the least amount of noise at its highest point. During which portions of the throw did the ball have its highest speed? The ball had its highest speed after its maximum acceleration, because gravity was the only force acting on it, so it gave the highest speed, while air resistance still gives a force, but it is barely anything because the object is not that high up compared to the motion sensor. Did the velocity change direction during the throw? If so, when, and how do you know? Velocity at first is decreasing in a positive direction, but at the peak, the velocity is zero, then its velocity increases in a negative direction. I know this because the graph shows the velocity of the ball. While the object is in the air, when should it have the highest acceleration? Lowest? Explain. The object should have the highest acceleration when it is released and right before it is caught because the acceleration caused by the throw is greatest after it is released, and it is also greatest just before being caught because the gravitational acceleration increases the velocity in the downward direction in the interval of time after its peak. The acceleration would be lowest at the peak because the velocity is slowing down to 0.