# Day 81: A Counter-Intuitive, Newton’s Third Problem

**Posted:**January 14, 2013

**Filed under:**School Days 2 Comments

This is a fun problem to see if students can truly apply Newton’s Third Law, that Kelly shared in our weekly G+ hangout a while back. An awesome, counter-intuitive problem (which I poorly worded in haste on the board; I would now write “What happens to the ramp if the block is sliding down at a constant velocity?”).

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Constant in what reference frame? relative to the ramp?

I don’t believe it matters whether it is defined as WRT the ramp or the ground.