Challenge: To design a cart and hanging mass system that can accelerate your phone at a desired rate.
Parameters: Your system should include a cart or sled to safely and smoothly accelerate your phone across the desk using a mass on the end of a string over a pulley. The mass of the entire system must be a constant, but you will be able to achieve different accelerations by having mass pieces you can move between the cart/sled and hanging object. The system must be released from rest and must be able to accelerate freely for at least 70 cm. Mr. J will provide you with a cardstock flag, which must be positioned on top of your cart/sled. The overall height of the sled (with flag) cannot exceed 20 cm.
Scoring: Your system will be scored based on your ability to hit a target velocity at a specific distance from rest. Eg. 1.65 m/s at 57 cm. You will need to calculate the acceleration required, and then adjust your system to achieve that acceleration. You will get two tries, and each try will count towards your score!
Score = | 0.02 + ∆vattempt one |-1 + | 0.02 + ∆vattempt two |-1
Rank will be based on score, with highest score earning highest rank.
Physics: We will be using this challenge to review all one-dimensional kinematics and dynamics topics from grade 11. I will detail these requirements as we proceed in class.
Modelling: Your model should include FBDs for the cart/sled/phone object and the hanging mass with all masses and forces (including friction) shown for a low acceleration case and for a high acceleration case. All calculations must be shown with steps, symbols, algebra, units, etc. etc.
Help/Hints: You should try to keep the non-moveable parts of your system light, to take maximum advantage of Newton’s Second Law. Friction can be unpredictable, so be careful to avoid sources of friction. Always use the same phone for the acceleration measurements. Use Phyphox to get raw data from which you can find the average acceleration, and see how constant it is. We have to assume constant acceleration for our formulae, but Phyphox will show you that the acceleration is not very constant, mainly due to elasticity in the string. Graph Acceleration of System vs. Unbalanced Force on System. If linear, calculate the slope and see if you can figure out what it means. Make sure all team members can do the calculations involved, and practice before the actual competition.
Quiz Topics: One-Dimensional Kinematics, FBD, Newton’s Laws, Measurement, Graphing
Online Text: chapter 2, 3, 4, 5 (one dimension only)