Newton’s 3rd Law and Vectors

Last week we finished our studies of Newton’s Laws and started to explore motion in two dimensions.

In order to explore the ideas of Action-Reaction we had robots perform a tug-of-war.  The question is, when is the tension greater.  When a robot pulls on a rope tied to the wall, or when two robots pull against each other?  This is based on a problem I call the Blind-folded-tug-of-war.

In a moment of frustration with the Ravenclaws, I decided they needed to be taught a lesson, grabbed some blindfolds (old concert T-shirts, Iron Maiden/Guns and Roses from 1988) and a long rope and we had a tug-of-war.  Once again, try as hard as the boys could, they were not able to beat….the wall.

Here you can see the girls pulling on one end of the rope….and then

Here you can see the boys pulling on rope….thinking they were pulling the girls….but really pulling the wall.  The tension is the same as the wall pulls back on the boys with an equal and opposite force.  Actually this is an old photo.


It has been a difficult week as far as physics goes.  Vectors and trigonometry can be a big challenge for many of the students.  The big goal is to try and make sense of the incline plane problem to close the book on our study of Galileo.  One can analyze this using trigonometry…of course, Galileo didn’t use that.  Interestingly, Galileo didn’t even use algebra.  All of his proofs were done using Euclidean Geometry…the old stuff.  Not what we teach students in school today, but you would have to study the books of Euclid just to read what Galileo wrote.  There is actually is a guy over at Harvard, Andy Engelward, who teaches a class for teachers on how to teach  real Euclidean geometry.  My wife took the class so I got to play around with her problem sets.  You have to perform all the proofs using only a piece of string and a straight-edge. Good thing I am not teaching geometry here.  That would be fun!