Summary - Lab 9 - Impulse and Momentum PDF

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Summary (including processes used, math and formulas, and question responses) for Physics I Lab 9 - Impulse and Momentum. I am the author of this document. It is my own original work. All of my lab summaries received a perfect score from the professor....

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Tucker Knutson Lab 9 - Impulse and Momentum Physics I – Saint Paul College 11-17-2011 Purpose In Lab 09, we investigate the Impulse - Momentum theorem as it relates Force over Time to the change of an object’s momentum. By using the traditional low friction cart and track with the appropriate data collection apparatus, we can effectively test the Impulse – Momentum theorem. A piece of elastic cord will tether the cart to a ring stand at one end of the track, which will provide force as the cart accelerates away from the ring stand and stretches the cord, giving it elastic potential energy. The cart will then reverse direction and move back towards the ring stand with its momentum conserved. Preliminary Questions 1)

By using an airbag during a vehicle collision, a driver’s velocity is brought to zero gradually by the bag’s opposing force due to air compression, which is significantly gentler on the driver than an immediate reduction of velocity by a hard object, such as a dashboard or windshield. 2) The clay will provide more impulse than the ball. Since the ball is quite elastic, its initial momentum is only partially transferred to the door and keeps most of it to itself as it bounces away. The clay however will transfer all of its momentum to the door; one would expect the resulting velocity of the door and clay combo to be

Vdoor+clay = momentumi / mass door+clay Procedure Materials - Low friction cart and track - Computer running Logger Pro with connected Vernier USB interface - Vernier Motion Detector and Force Sensor - Ring stand - 500 g mass Setting it up The track was laid and leveled such that the cart did not move when centered on the track, and the ring stand was placed on the table at one end. A force sensor was then fitted on to the ring stand with its sensor post facing the cart on the track. An elastic cord was connected between the force sensor post and the cart, and a motion detector was placed on the opposite end of the track facing towards the cart. A 500 g mass was placed on the cart and fixated with masking tape; a scale measured the cart’s total mass to be 0.522 kg. With the force sensor set to 10 N and the “19 Impulse and Momentum” preset opened in Logger Pro, we were ready to begin trials. The experiment We placed the cart close to the force sensor, zeroed the cart’s location in Logger Pro, and made sure to place the cord in such a way that it would not affect the path of the cart’s wheels and produce flawed data. We practiced releasing the cart and observed a smooth elastic “bounce” before returning back to our hands. After collecting several subsequent runs, we chose one that seemed very natural and unaltered by hand movement or cord interference. Using Logger Pro’s analysis tools, we recorded the cart’s average velocity before and after the impulse and recorded the values in our data table. We then found the time duration and average force of the impulse and recorded the value in our data table. A second trial was performed and appropriate data recorded. We then changed the elastic material to a slightly more aggressive cord and repeated the trial process two more times.

Data String Material 1

String Material 2

Data Tables

Analysis 1) I measured the change in momentum in units of kg(m/s).

ΔP=-(Pfinal-Pinitial)

2) Impulse: I=N • s 3) See Data. Percent difference between initial momentum and final momentum. Sample calculation to the right of lower table. 4) My percent difference values were all under 20% and over 15%, giving my data a spread of 5%. This implies that a consistent factor (like cord interference) adjusted all of my values roughly 15%, and my effective error ratio is 5%. With that in mind, I believe my data supports the impulse-momentum theorem. 5) The top of the force vs time graph is gently curved and not significantly higher than the average. A way to apply the same impulse with less force is to increase the time that the force is applied and decrease the magnitude of force. 6) Indeed. 7) The stronger material (material 2) produced graphs with sharper curvatures due to higher force magnitude. 8) Our data shows that the time duration was the same for material 1 and material two while the force magnitude of material 2 was greater. This doesn’t support the calculated data; material 2 should have a proportionally smaller time due to the increased force. 9) Stronger cord = less time of impulse = greater force of impulse

Error Analysis As stated in analysis question 4, some part of our system must have been affecting our results. Analysis question 9 adds to that conclusion by implying that the suspect of error had something to do with the time data collection. This leads me to believe that the motion detector was being influenced by something other than just the carts position on the track. Perhaps some noise that is close to the detector’s audio emission frequency was being erroneously detected. Conclusion After performing and analyzing this experiment, I am convinced that the Impulse – Momentum theorem does indeed exist. With consideration of potential errors, our data supports the notion that momentum is conserved, along with energy, before and after an impulse. The cord cannot add energy to the cart’s motion; it can only store and release energy. The cart’s momentum before the impulse loads the cord with elastic potential energy until PE = 100% and KE = 0%. It then releases the energy back on to the cart until the KE = 100% and PE = 0%....