Julia,+Hannah,+and+Marissa's+Accelerated+Motion+Lab

=Accelerated Motion Lab= October 26, 2009


 * Participants**: Julia Kravitz, Hannah Mollmark, & Marissa Marton


 * Purpose**: The purpose of this lab is to observe motion that is accelerating and be able to determine between an accelerated motion and motion of a constant velocity. In the experiment, the acceleration of a hoverpuck traveling over a flat surface and the acceleration of a free-falling object were to be determined, and velocity vs. time, position vs. time, and acceleration vs. time graphs made.


 * Brief Description of Experiment**: During this experiment, we used a hoverpuck and a 500g weight. We used a device called a tape timer which marks points on a piece of paper every 1/60th of second. We attached the strip of paper to the hoverpuck, and as we pushed it and it traveled across the table surface, the tape timer made points on the paper as it ran through the device. We could use these points to determine how fast the hoverpuck was moving and by how much it was accelerating because we had it's movement over small time intervals of 1/60th of a second. We used the same procedure with the weight which free-fell from the height of the doorway of the classroom and from the second-story staircase in the school. On the strips of paper, we measured the distance of every point from the first and plotted them onto graphs. By using formulas like the calcualtion of the velocity in between each point (by finding the distance each object traveled from point to point and by dividing by 1/60 of a second), we were able to graph the points on position vs. time, velocity vs. time, and acceleration vs. time graphs.

A tape timer (a.k.a. ticker timer or spark timer):

Distance traveled over time:
 * Data**:

**Sample Calculations:** velocity = distance / time || acceleration = ∆ velocity / time  || **Results**: The acceleration of a 1kg object (dropped from a short distance) is equal to 1070 cm/s/sec. The acceleration of a 1kg object (dropped from a long distance) is equal to 906.5 cm/s/sec. The acceleration of a Hoverpuck is equal to 8.019 cm/s/sec. We calculated all of these values by measure the slope of the velocity vs. time graph.
 * //Velocity// || The velocity in centimeters per second was calculated by dividing the distance traveled by the time elapsed. The time was measured in 1/60th of a second.
 * // Acceleration // || The acceleration in centimeters per second per second was calculated by dividing the change in velocity by the time elapsed.

1. Which objects that you studied were clearly accelerating? How can you tell by looking at the motion of the objects? How can you tell by looking at the position vs. time graph? How can you tell by looking at the velocity vs. time graph?
 * Lab Questions**:

The free-falling weights, from both the doorway and the stairs, were accelerating. This can be determined by looking at the motion of the objects in that they gain velocity as they fall. When they are first released, they travel slower than right before they hit the floor. You can tell that the objects were accelerating by looking at the position vs. time graph in that over time, the position changes and gradually increases the rate at which it moves. The line shows the movement of position in an increasing curve. The acceleration can be determined by looking at the velocity vs. time graph in the same way as observing the position vs. time graph. The line depicting velocity is curved upward which shows that over time, the velocity increased more and more, thus showing acceleration--a change in velocity.

2. Which objects that you studied were not accelerating/were accelerating slightly? How can you tell by looking at the motion of the objects? How can you tell by looking at the position vs. time graph? How can you tell by looking at the velocity vs. time graph?

The hoverpuck didn't show any acceleration. This can be seen from looking at its motion in that it looks like it stays at a rather constant velocity as it travels across the flat surface of the table top. The lack of acceleration can be observed by looking at the position vs. time graph in that the line of position shows a steady, linear depiction of position over time; it moves and changes its position at a constant rate. The fact that the hoverpuck doesn't accelerate can be determined by looking at the velocity vs. time graph in that the velocity is a straight line over time showing no dramatic change in velocity which is acceleration. A constant velocity means no acceleration.

3. What was the value of the acceleration of the 1kg object? Can you find a relevant value to compare this to a "free falling object" near the surface of the earth? How do your values compare (% difference)? **Follow-up:** If you also did a 100g object, what was the acceleration and how does this compare (% difference)?

The value of the acceleration of the 1kg object was 906.5 cm/s/sec. A relevant value to compare this to a "free falling object" near the surface of the earth is 980 cm/s/sec. This number is the accepted value for the acceleration of a "free falling object." The values compare (% difference) in that our value is 7.5% less than the accepted value. We did not do a 100g object.

4. What is meant by a negative acceleration?

Negative acceleration means that velocity is decreasing. This is because the acceleration equation is change in velocity divided by the time elapsed, so if the change in velocity (final velocity - initial velocity) is negative the overall acceleration would be negative.


 * Conclusion**:

Our Identification of Accelerated Motion consisted of observing a hoverpuck and a 500g weight dropped from about 2 meters and from the top of a stairwell. Our experiment did produce a fairly valid and reproducible result. This is because we generally had to test more than once due to issues with timing and with the long, slim sheet of paper. We feel that since we tested each a few times to get a more accurate result, that our data can be reproducable. However, it will not be completely accurate because of human error (like dropping the weight differenty, holding the accelration devise differently, or maybe slight mistakes in height measurement could all be reasonable causes of slight variations).

Our experiment results could differ from any accepted value (in addition to what is stated above) in that we did take wrong measurements when we measured the long / slim sheet of paper. Instead of starting out at 0 centimeters, we started out at 1 centimeter due to some confusion. This would alter our results for both the 500g weight dropped from the door and for the 500g weight dropped from the stairwell. However, the hoverpuck measurements were accurate.

A simple improvement, however a time consuming improvement, would be to do multiple trials of the hoverpuck, the 500g mass dropped from the stairwell, and the 500g mass dropped from the doorway. By having solid data for multiple trials, we could then average them together to get a more reporducable result. It still may be slightly off but it would be much more helpful in determining if the result is reproducable or not as opposed to one single trial for each.