Guilty Until Proven Innocent

Problem:

How can you use the conservation of momentum to prove to a judge that you were not speeding and therefore do not deserve a ticket for the collision?

Materials:

Paper, Logger Pro, video, safercar.gov, protracter, ruler.

Procedure:

You leave the school teacher's parking lot and are traveling north when you are broadsided by a car traveling east. The collision occurs in a school zone with a speed limit of 20 mph.  The impact throws you into the band practice field.

Following the collision the police officer determines that both vehicles had a speed of 22 mph (9.8 m/s). The driver of the other car is an adult and claims that you were speeding and consequently should receive a ticket. You are to prove your innocence by using the conservation of momentum.

Research:

What type of a vehicle were you driving?  What type of a vehicle was the other driver riding in?  Look again at the safety and the mass of these vehicles at the NHSTA site (http://www.safercar.gov  ).  Use the same vehicle you looked up earlier this week.

Your vehicle_______________           Mass or weight____________

Their vehicle_______________           Mass or weight____________

Decide on the units for your momentum and record here ____________

Draw a diagram of the two cars just prior to impact. You were headed north, the other car was headed East. Choose a scale (e.g., 1 cm = kg m/s) or freehand draw a diagram of the vehicles before AND after the impact your calculation .  

There are two possible cases.  In Case 1, you were going 20 mph.  In Case 2, they were going 20 mph.  One things for sure.  After the collision, you were stuck together and both of you traveled at 22 mph.

Do one set of calculations for each Case.

STEP 2:  MODEL THIS COLLISION USING two balls of similar diameters but different masses.  Because the collision described above is inelastic, the balls must stick together and slide after impact.

Summing Up (each person does this individually,1/2 to 1 page, and hands it in paper clipped to the diagrams)

1. Qualitatively explain, using your diagrams, how you know that you were not going faster than the adult. Remember that a ticket means higher insurance rates and a large fine.

2. Do you think you were you speeding?

3. How would angles affect your logic?

4. What evidence of impulse or guilt would the police collect in this action?
5.  Based on the safety rating of the vehicles involved, what do you think the extent of the injuries would be?
6.  What role did impulse play in the safety factors present in your vehicle?   

Momentum Actvity

Activity 1  http://www.physicsclassroom.com/class/momentum/Lesson-1/Momentum-and-Impulse-Connection  (there are 7 problems, and you must do at least 4.  SHOW WORK)
Activity 2  http://www.physicsclassroom.com/class/momentum/Lesson-2/Momentum-Conservation-in-Explosions (Do all 5 problems.  SHOW WORK)


=======Second 45 minutes===========

Activity 3 should be downloaded to a computer and filled out.  http://phet.colorado.edu/files/activities/3777/Solar%20System%20PhET%20momentum%20conservation.docx   Do not kill a tree--simply write down the work to show your answers.



Hand in at the end of the hour.  Each person should hand a sheet in.

Pool Table work

Part 1

1.  Determine mu of your pool table surface.#

2.  Determine the elasticity of the bumper using p(b)=p(a)  using logger pro and the Video Capture option.#

3.  Make a drafting sketch of the pool table using autodesks, google sketchup, or a paper pencil model.  It must be to scale.#

4.  Practice making shots where the ball recoils at 90 degrees, where the ball recoils at 180 degrees,  > 90 degrees, and the ball recoils at < 90 degrees. #

Part 2:  

1.  Use a cell phone or flip camera to document your expertise in #4.  #

http://www.wikihow.com/Play-Pool-Like-a-Mathematician

http://billiards.colostate.edu/threads/position.html

http://iptv.pbslearningmedia.org/resource/rttt12.math.anglepool/the-angle-on-pool/

http://www.angelfire.com/ks3/poolmath/mathematics_of_pool.html

http://merganser.math.gvsu.edu/david/reed03/projects/fowler/poolcalc.html

http://billiards.colostate.edu/threads/position.html

Part 3:

1.   Hand in a scaled model of your pool table that includes top and side views.  This may be done using graph paper, sketch-up, or a CAD program, but the final product must be digitized.

2.  Create a Logger Pro artifact for the two collisions that includes the dot diagrams on the video and your calculations from Monday.  The first one will use only the x-axis.   The second one will use the cue-ball going off at a right angle.  Send me a screen shot of these two videos after analysis
3.  Hand in the analysis for the 1-d  collision of the ball, showing me a) the momentum before the collision, b)the momentum after the collision, c) the net time the two objects  were in contact, and d) calculations of the change in momentum and the impulse Force.  This is most easily done using paper and pencil and then taking a picture of the finished project.  (Hint:  use the mass of the cue ball and the cue stick, or the mass of both of the balls)
4. A picture of your group and your pool table must be included.

Part 4:
Evaluate a pool table that is not your own from a different table cluster.

Net forces activity

Part 1:  use the applet found at http://phet.colorado.edu/en/simulation/the-ramp

First, take a look at the page found here.   http://phet.colorado.edu/en/contributions/view/3143 It has lots of labs, some good, some bad, that help people to figure out the basics of mu, horizontal force net, and forces on a ramp.

Pick one of these labs and go through it. Do not pick the same lab as another group at your table. TEAMS ABOVE THREE WILL NOT BE ACCEPTED.   Turn it in today.

Part 2:  to be done individually, on paper, while sharing the computer applet.

DESIGN TEST:   Last Friday, we had a net force worksheet that we have not graded--yet.  You will need to use this applet to help design a student lab that is not boring and easier to understand regarding net force on a hill.  The lab should create understanding for mu on a hill, force body diagrams, and use net forces to answer the following question:   Does the mass of an object change the mu of an object moving with net force along the ramp?.   

State the purpose of your lab:

Give directions, as needed:

Collect evidence:

Tell me what is analyzed:

Part 2 is due on Friday.

Egg dropp