10/2/09 Class

The first thing we did in class on Friday, was to get back our 3E and 3F homework. We then talked about how the earth has a huge mass, which means it has a huge inertia. The moon and sun can change the velocity of the earth, it's always changing because we're orbiting. We exert force on the earth, because the earth exerts a gravitational force on us, but the force we exert is not enough to change the velocity of the earth. Footprints are proof that we put force on the ground. THe normal force of us on the earth equals the gravitational force of us on the earth, but if we are in quicksand there would be less normal force.
We went over many of the homework problems. The solutions are on the blog. Just dropped, a heavy dart and a light dart have the same acceleration. a=fnet/m, and if the darts were shot by a gun, the mass would be larger for the heavy dart. So it would have a larger acceleration. This happens because by the time the dart has left the gun, it already has a larger velocity.
When two vectors are added, the sum can be anything from zero to the sum of the lengths of the vectors. If you're confused about how to arranget the vectors, ask yourself "Is this something I could walk?"
The vector activity is due Tuesday. The vector activity sheet shows us how to do vectors on the calcuatlor, but be comfortable doing this with a ruler and protactor before you use the calculator. Our test is tomorrow. Study. Don't forget about the Unit 3 Review Sheet for practice.
The next scribe is Margaret