# Day 97: What If There’s More Than One Force?

College-Prep Physics: What if there’s more than one force? We used dueling fan carts and a motion detector to predict and test the outcomes of several scenarios. It turns out that …

2 carts, 1 fan on high (3F) ≈ 0.3 m/s/s

2 carts, 1 fan on medium (2F) ≈0.2 m/s/s

2 carts, 1 fan on low (1F) ≈0.1 m/s/s

So, what happens in the balanced cases?

Not terrible surprising. How about the unbalanced cases?

Then we returned to the PhET force and motion sim. We pushed the sleepy dog with 200 N (F1), turned friction on/off (F2), and looked at the resulting acceleratations:

Then I challenged the students to determine:

• When there’s friction, how hard should we push so that we get the same acceleration as without friction?
• When there’s no friction, how hard should we push so that we get the same acceleration as with friction?

Students made their predictions and we tested using the simulation. Now we can modify the equation we derived yesterday and change force to net force.

##UBFPM