Teach Fzx Tuesday - 'g'

'g' is NOT the "acceleration of gravity."

I mean, it is, but it's also known as the "gravitational field strength."  Teaching FORCES FIRST and starting with static equilibrium has convinced me not to use "acceleration of gravity" yet for several reasons.


First, since nothing is moving, 'g' has nothing to do with acceleration.  It's really just a value used to calculate the weight of an object given its mass.  As such, "gravitational field strength" makes a LOT more sense.  Different locations in our solar system and in our planet have different gravitational field strengths and objects would have different weights in those different locations.

Using "gravitational field strength" also provided the opportunity to talk about the concept of "fields" in physics.  A conversation yesterday in Conceptual Physics:

     Student "When I think of fields, I picture grass and a big space..."

I was impressed and happy that he asked, complimented him on that fact, and responded:

     Me "Back in the mid-1800s, scientists were struggling with explaining how the Sun attracted Earth, how magnets attracted metal, and how negative charges repelled each other - all without contact.  They came up with the concept that space was altered around a mass, charge or magnet and called it a field...." 

Great opportunity for a big idea in Fzx.

And those niggly units.  They always struggle with units.  It does not make sense that multiplying kg by m/s/s would yield N.  If, however, we use W=mg and g has units of N/kg, it's obvious that the product on the right side yields N.  I like that.

Eventually, we will also use "acceleration of gravity" and that will allow a discussion of gravitational mass vs. inertial mass and why they are the same.  It'll be fun and that's what I'm here for.

So now I know that "gravitational field strength" is a lot better than "acceleration of gravity."

Until things start accelerating.