Reflection: Complex Tasks Discovering Newton's 2nd Law - Section 4: Closure


For homework, students graph their data and analyze their results.  Though this is not typically how you graph scientific data, I tell the students to put the dependent variable (acceleration of cart) on the x-axis and the independent (applied force/hanging mass) on the y-axis.  

The reason for this is when they analyze the data, it is easier to see that the slope of the line is the mass of the cart.   The equation for a line is y = mx+b which becomes F=ma if graphed the way described above.  If they graph the variables the other way then they end up with the mathematical relationship of a = (1/m)F.  Though it is not mathematically difficult to get to F=ma, I have found in the past that this is enough of a barrier for most students that they are not able to figure out on their own how the mass of the cart fits into the analysis. 

This Student Work sample is an exemplar. It has a simple free body diagram, detailed procedure and the graph shows a best fit line. Students often connect the dots on their graph.  Sometimes I'll display a kids menu or some other "connect the dots" picture that shows a cuddly bunny and tell students that THIS is when you should connect the dots.  With scientific data, you must draw a best fit line.  

  Complex Tasks: Analysis Reflection
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Discovering Newton's 2nd Law

Unit 1: Forces in One Dimension
Lesson 4 of 11

Objective: Using a cart and pulley, students will determine the relationship between net force and acceleration for a fixed mass .

Big Idea: F=ma can be determined experimentally.

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cart and hanging mass
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