After we discussed the two types of balances, everyone went to the lab table and we discussed the free body diagram of a horse pulling the wagon. "According to the horse", he should not be able to move the wagon because every force he puts on the wagon, the wagon counteracts equally and oppositely. After much discussion, we came to the conclusion that the friction of the horse pushing against the ground gives the horse the extra leverage to actually move the wagon.
The final activity we did in class was to begin the vector lab. Mr. Burk had a contraption of two rulers screwdrived together so that one ruler went out 50 cm or 1 spring unit before the other ruler crossed it perpendicularly. First we did a control test of 1 spring unit, and then wrote predictions for the two spring units. Most everyone said it would be exactly double even though the springs go out at angles and are not pulling straight in front of the cart. It ended up that the two spring units on the ruler contraption only pulled the cart with an acceleration 0.7 m/s/s faster than one spring unit, which was not close to double. We then tried to figure this out, and did not finish the discussion, but so far it looks as though it involves finding the leg of the 45 45 90 triangle and doubling it to find the amount of force.
Homework: Finish the Inertial Balance lab and Homework 3E
Next scribe is Paxton.
1 comments:
A few follow up points:
1. The inertial balance doesn't measure weight (the gravitational force of the earth) it measures inertial mass, which is different from gravitational mass, but turns out to be exactly the same when you measure the two quantities.
2. The horse's major mistake is not drawing a fbd, and seeing that the two N3 forces do not act on the same object. The horse can move forward so long as the force the ground exerts on the horse (friction) is larger than the force the wagon exerts on the horse.
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