group+002

Overview: Our group will be doing a recoil problem. We will have Erika put on rollerblades and hold a backpack at rest. She will then throw the backpack out as hard as she can and we will measure her mass and velocity, as well as the mass and velocity of the backpack; and by setting up a recoil problem, determine if momentum was conserved.

Data Collecting: We will collect our data by fist getting the masses of Erika, The rollerblades and the backpack. We will then use a scale that measures Newtons to determine FF. This is possible because if we can move her at a constant speed we will now that the FA will be equal to FF. We can the set FF equal to MA to solve for A. Once we get that we can set up a vififdat problem because we will have A, delta X, and VF. We will then solve for her velocity As for the bowling ball, that is a bomber problem and we will make sure that Erika throws the ball from the same height every time. We then have enough information to find the velocity of the backpack. Then, we can set up a recoil problem, and solve for the momentum.

Materials: Backpack (filled with heavy books), Roller Blades, Scale, Scale that measures Newtons (for the force of friction), Meter Stick, and Tape Measure.

Saftey Precautions: We must make sure that we throw the backpack on carpet because of it's immense weight. Also, we need to make sure that Erika does not fall while on the roller blades. media type="file" key="DSCN1238.MOV" Procedure: 1. Using the electric balance, find the mass of Jake with the roller blades on. Then find the mass of the backpack filled with books. 2. Find the force of friction that will be acting on Jake. We will do this by using the small newton scales to pull Jake(on the roller blades) at a constant speed. Once he is moving at a constant velocity, with no acceleration, we will read the small newton scales. This force required to keep Jake moving with no acceleration will be equal to the force of friction, acting in the opposite direction. 3. Jake will then stand with the front edge of the rollerblades exactly on the edge of the doorway,between the tile floor and the carpet. Since there is less friction on the tile than the carpet, there will be less energy lost to heat. Also, this way the backpack doesn't land on the tile floor, which might damage the floor or the backpack. 4. Jake will hold the backpack at chest level, with his elbows bent at roughly 90 degrees. we will then measure the height of the backpack, and will make sure the bp starts at the exact same height for every trial. 5. He will then throw the bp straight out away from him. He will make sure not to throw the bp at any angle, as this would make it into a cannon situation, as opposed to a bomber. 6. One person will measure the distance the bp went from the edge of the doorway. At the same time, another person will measure the distance that Jake recoiled when he threw the bp. This person will measure from the doorway edge to the front of the rollerblades. 7. We will repeat the experiment until we have enough trials to ensure accurate and consistent results. 8. we now have all of the data we need to do a bomber problem. the data we have is: X -acceleration(in a bomber, ax=0) -delta x(the distance the backpack went) Y -initial velocity(it is 0) -acceleration(gravity) -delta x(the height the backpack starts at) 9. From this we take the data in the Y and solve for time using a vivfdat equation. Since time is the same in both directions, we can then use it in the X column. 10. By plugging time into a vivfdat equation, we will be able to find the Vi of the backpack. 11. Since we know the velocity of the bp, and we know it's mass, we can easily find it's momentum. we will do this by using the equation p=mv. 12. Now we will move onto the other part of the problem, how far I move back when I throw the bp. we have enough information to find out my initial velocity right after I released the bp. we have: -force of friction between the rollerblades and the floor -displacement(distance between the front of the skates and the doorway) -final velocity which is zero, because I end up at rest 13. Using the force of friction, which is the only force acting on me after I release the bp, we can use Fnet=ma to find the acceleration. 14. From here, it is a simple vivfdat equation to find the initial velocity. Once we have the velocity, and we know my mass, we can use p=mv to find my momentum. 15. Now we have all the information we need. If every bit of the momentum was conserved, then my momentum should be equal but opposite the that of the backpack, so that when added together they will equal 0. This is what we want because in this situation, both objects started at rest, giving the entire system a total momentum of 0.

Conclusion: In our experiment, due to human error, we were not able to prove that momentum was conserved. Our experiment ended up having a 200% error, which shows just how much human error we had. But, with a recoil problem, no matter what momentum you end up with, you will get a 200% error, unless you end up with 0. Our biggest error was using Erika as the person throwing the backpack. Because she is so light, she was basically throwing 1/5 of her weight and the backpack was very heavy for her. Therefore, she was probably throwing the backpack upwards a little, turning our experiment into a canon problem. We corrected this mistake though by changing the person throwing the backpack. However, we still had many sources of error. First, when the roller blades moved Jake backwards, they would sometimes move back and forth before we had a chance to measure how far they had originally moved, so that measurement was off. Also, when the backpack hit the floor, we simply estimated around where it landed instead of using carbon paper to make sure we had a more accurate spot. But, it would be very difficult to use carbon paper to measure where a backpack landed because of it's mass. The backpack's size also added room for error because we did not measure from the floor to the same spot on the backpack every time. Similarly, because Jake may have adjusted how he held the backpack during each trial, we may not have measured accurately from the floor to Jake's pinky. Our measurement for force of friction probably added a lot of error too because the person pulling Jake did not move at a constant speed, did not hold the spring scales parallel, and both Jake and the person pulling him moved their hands around and did not keep them in the same spot for the whole trial. But all in all, having Jake throw the backpack yielded much better results than having Erika throw it. When Erika did the experiment, we were off by approximately 14.25kgm/s and when Jake did the experiment, we were only off by negative one third. Therefore, it was the right decision to have Jake throw the backpack, because although he is heavier, he was able to throw the backpack with more force, sending himself backwards double the distance than Erika moved.