Lab-11

Sammy Fisher, Alex Feldman, Sammi Blake, Chelsea Figman Period 8 2/2/10- 2/10/10

Lab: Impulse of a baseball

__**Objective:**__ How does the impulse of a softball on a box compare to the impulse of the box on the softball.


 * __Hypothesis:__** The impulse of a softball on a box and the impulse of the box on the softball are equal.




 * __Calculations:__**

1. Work done by friction bringing the box to a stop Wfriction= f X d Wfriction= 6 (.19) Wfriction= 1.14 J

2. Kinetic Energy the box-ball system had KEballbox- Wfriction= 0 KEballbox= Wfriction 1.14 J

3. initial velocity of the box-ball system KE2= 1/2mv2 1.14= ½ (1.483) v2 v2 = 1.5.4 v= 1.24 m/s

4. momentum of the box-ball system Impulse=m*delta v Impulse= 1.483 (0-1.24) Impulse= 1.483 (-1.24) Impulse=-1.240

5. same as number 4

6. + 1.240

7. Velocity of the ball recorded by the motion sensor Impulse= m* delta v -1.84=.183 vi vi=10.05

Percent difference: measurement-calculation/ average (measurement +calculation) x 100 12.51-10.05/ 11.28 x100 % difference: 21.8 %

Analysis/Discussion Questions In order to complete our calculations during this experiment, we assumed that the acceleration of the softball was constant throughout that kinetic energy was proportional to the force of friction and that momentum and impulse were equal. Also, because of the direction the box moved, we knew that the momentum of the box on the ball was negative so we were able to predict the momentum of the ball on the box to be positive. We could have calculated the initial velocity using kinematics or dynamics as opposed to calculating the initial velocity using momentum, energy and conservation. Newton’s third law states that for every action there is an equal an opposite reaction which really means that these forces are going to be opposite in direction but equal in size. We used this law to demonstrate the relationship between impulse and momentum because the two will always have equal but opposite force. Impulse- J=m(change in)v J=(1.483)*(-1.24) J= -1.84 kg m/s
 * 1.)** **What assumptions did you make in order to complete the calculations in this experiment?**
 * 2.)** **How else could you have calculated the initial velocity**
 * 3.)** **Why is the Impulse-momentum relationship useful?**
 * 4.)** **Find the magnitude of the impulse delivered to the object**

Momentum and Impulse are equal so the momentum will be (+) 1.84 N/s
 * 5.)** **Determine the change in the object’s momentum.**

Use the formula: m(Vf-Vi) Mass: 1.483 kg Vf: ? Vi: -10 m/s M(Vf-Vi)
 * 6.)** **If the object’s original velocity was -10 m/s, calculate its final velocity**

1.483 (Vf – (-10)) 1.483 (Vf+10)= 1.84 1.483Vf +14.83=1.84 1.483Vf=-12.99
 * Vf= -8.76 m/s**

The magnitude of the average force would be: __m(Vi)+ m(Vf)__ 2 __1.483(10.05)+1.483(1.24)__ = 8.37 N/s 2
 * 7.)** **What was the magnitude of the “avg. force” acting on the object during the time graphed?**

To make sure that the box hit at the same place at the same speed for every trial we could use an automatic softball thrower which would guarantee more accurate and consistent results. Also, to ensure that the ball hits the box in the same spot for every trial we could mark a spot on the box with an “X”. A real life application of this concept would be how detectives determine the final velocity of a car that got in an accident to check and see if the driver was speeding or not. They could also use these concepts to determine the stopping time of each vehicle.
 * Conclusion: (Part 3) Implications for further discussion**
 * I.)** **How would you change the lad to address the errors?**
 * II.)** **What is a relevant real life application of this concept? (why is this important to know/understand?)**

__**Conclusion:**__ In this lab we were able to calculate the velocity of the softball as it was being thrown into the box. We saw that the greater the velocity of the ball the more force it had while hitting the box, which made the box move further back. Our hypothesis was proven correct. The impulse of a softball on a box and the impulse of the box on the softball are equal. In the lab we had a large percent error, which could have been caused by a plethora of problems. One is the placement of the box, and if the ball forces it to move on an angle on impact, then it is measured differently then other throws where the box moves straight back. Another cause for error is the paper inside the box. The paper was thicker in some parts of the box than others so when the ball hit different parts then the force would be different. To fix this, we could have used a ball toss machine where it is guaranteed to hit the same spot of the box every throw. Due to all of these imperfections, our percent error was high.