Purpose:

Calculationally this is not a complex lab but it relies on a clear understanding of Newton's 1st Law and the kinematics of constant velocity. Because there is an experimental challenge in this lab that involves some modest risk to the participants you need to be sure you understand your data and it's variability to manage that risk.

Procedure:

The standard tools for doing science/physics are good thinking, paper and pencil, physics concepts, measurement tools, and critical thinking. A python notebook is available from the PH211 repo that has all the python tools (numerical and graphical) that you need to execute the lab and create your lab report. Here is your challenge:

Either in the hallways of the building or outside on the sidewalk two intersecting paths will be laid out. You will be provided with kinematics carts to sit on, meter sticks or tape measures to measure distances, and you hopefully have access to stop watches or timers on your phone. Your challenge is to push one of your classmates along each path on a cart at constant velocity so that they do NOT crash into each other at the intersection subject to a number of constraints. To do this you will be need to be able to determine/test how consistently you can make the cart move at what velocity.

1) Some groups will be required to calibrate their speed to fall in the range [0.5, 0.8] m/s and other groups will be required to fall in the [1.2, 1.5] m/s range. These ranges for the fast and slow group are mean to provide a modicum of safety for this challenge. Your group will be randomly assigned to a speed range. You may not move on to the challenge portion of the lab until you can demonstrate that you know, from data, your speed and the variability (standard deviation/mean).

2) Starting points for each leg of the challenge will be indicated with chalk and the distances to the intersection provided to you. Each group will be randomly assigned a partner group so that a 'slow speed group' will be paired with a 'higher speed group'. For each pair of groups there will be a mechanism for assigning which group is on the short leg and which group must pass through the intersection first.

Constraints

i) The carts will need to pass within 1.5 m of each other at the intersection with a designated 'cart' passing through the intersection first.

ii) The 'cart pushers' will be blindfolded for the actual test and the team can only say 'start' or 'abort' until they have passed through the intersection point.

iii) All calibration and experimentation will take place away from the actual challenge site.

3) You must present a coherent plan that is supported by experimental data and plots before you will be permitted to perform the experiment. Getting the plots to accurately describe what you are planning may be one of the bigger challenges in the lab. This caution is based on the actual experiences of past students.

4) The rules committee reserves the right to change or adjust any of these contraints as required to maintain the safety and integrity of this challenge event.

CONCEPTS:

• Experiment design
• multiple representations
• testing experiments
• kinematic tools and calculations

LAB DELIVERABLES:

I) After the usual introductory description of the lab in your lab notebook describe and illustrate (sketch) the challenge problem. You will embed an image of that sketch in your notebook in the apprpriate markdown cell. Describe, with clarity, the tests you decided to perform and the data you needed to construct a solution to the challenge.

II) Present the data and calculations you used to calibrate the velocity of your group's 'cart'. In that presentation you must also provide data that supports your estimate of the variability (standard deviation/mean) for the 'cart's velocity. Present the physics model of your cart's behavior as a plot with the +/- 1 sigma possibilities as well.

III) Present your intended solution to the challenge problem with a clear of the uncertainties in the times, positions, and velocities of the carts. To do this you will need to share data with your partner group so that you can accurately represent your solution as a plot in your notebook. Identify the features of the plot that indicate how far apart you predict the carts will be at the intersection point, which cart gets there first and by how much time, and how the plot indicates how much one of the groups needed to delay their start.

IV) Reflect on and analyze the success of your solution. Present a plot showing a possible solution that reverses the order of arrival at the intersection point but otherwise meets the criteria of the challenge.

Cart Crash Rubric: