Day 45: What Affects Gravity?


Physics 11 – The classes continued with their examination of things that affect gravity.  In this lesson, we went through how gravity between two objects results in equal forces acting on each object, regardless of the mass of the objects.  I closely followed the outine from Preconceptions in Mechanics, and how Frank Noschese worked with his classes.

I opted to have up to three students pull on spring gauges, with each of their gauges hooked onto a gauge of another (fourth) student.  What we saw was that the total force of the three students (3 x 3N each) equaled the force experienced by the fourth student (9 N).  Students verbally expanded on this idea, but commenting how if there were a billion students pulling with 3 N each, the total of their pull would be 3 billion Newtons, as would be the pull of the singular student.  This was our model to represent small particles, where the Earth is made up of billions of small particles.

We followed this lesson by looking at normal forces. I was surprised that almost all the students immediately saw what a normal force was, and that it balanced against the force of gravity.  In our discussions, there seemed to be very little misconceptions.  Students were also interested in extending their idea of force equality in pairs.  I still zoomed through some demos of a chair spring, foam and vehicle suspension spring (increasing spring constant), and ended with the deflected laser on the desk demo.  They found the laser deflection to be interesting albeit not surprising.


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