# Day 51: Elevator Forces Testing Experiment

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College-Prep Physics: As we explore more about balanced and unbalanced forces, students were asked to predict how forces behave while riding an elevator. We followed up our predictions by riding the school elevator while standing on a scale.

It is important to note that the scale reads the upward normal force, rather than the gravitational force (though sometimes the two forces are equal in magnitude). To demonstrate, a student stood with both feet on the scale, then just one foot on the scale and the other foot on the desk. By shifting is weight, he was able to get the scale to read different amounts, yet the earth’s gravitational pull (his weight) remained the same.

(In years past, I’ve done this activity after introducing Newton’s 2nd Law so students can also calculate the acceleration of the elevator. I decided to use it earlier so we can see another easy (and quantitative) example of the connection between balanced/unbalanced forces and constant/non-constant speed.)

Here’s a copy of the activity:
LAB ELEVATOR PredictTest UBFM vs BFM 2014

##BFPM