Flyin' Carts!

Fall finally seems to be creeping in – it was almost chilly this morning! A word of note: the classroom can get quite cold in winter, so have something you can slip on in class stashed in your backpack.

Honors Physics discussed Newton’s 2nd and 3rd Laws of Motion and some of the misconceptions associated with these laws. For example, Newton’s 2nd Law is not simply a formula – it is a relationship between forces and an object’s inertia. Newton’s 3rd Law always gets mangled – action and reaction refer to the forces involved, not the responses of the objects. Response (acceleration) is dependent on the individual objects’ inertia. Also, the phrase “action-reaction pairs” implies a time lag that does not actually exist. When objects contact, the forces are generated instantaneously and simultaneously. Lastly, remember that these forces do not result in equilibrium – they act on different objects, not on a single object. Tomorrow, we will discuss weight and the normal force and should have time to make an inroad into friction. For the homework, you can omit #24 and 25. For some reason, the book expects you to know how to work with weight and its components before actually showing you how!

Physical Science B reviewed their Newton’s 2nd Law of Motion problems and began a discussion of gravity. The gravitational force between any two objects can be calculated using the formula: F_g = (Gm₁m₂)/r². The problems set you have for homework tonight uses this formula to solve for force, mass or distance between objects. Talking to a couple of folks today, I think we might need a little review on the most efficient way to use exponents on your calculators. When working with scientific notation, using the caret key is not the best way for many brands of calculators. It is too easy to make a mistake. On the TI series that many of you have, type in the number, then hit the 2nd key, then the “,” key with has an EE on top. Then, type in your exponent, using + or -, as appropriate. The caret key is the key to use when typing an exponent for a number, something like 5⁸. Click Here for the answer key for your worksheet problems.

Physical Science E worked on a lab that allowed students to assess the effect of mass (inertia) and force on the acceleration of an object. First, a variable mass was subjected to a constant force and, then, a variable force acted on a constant mass. From yesterday’s discussion of Newton’s 2nd Law of Motion, the results should make sense. Acceleration was directly proportional to applied force when mass is constant (greater force, greater acceleration) and inversely proportional to mass (inertia) when force is constant (greater inertia, less acceleration). Only a few carts went flying off of the lab tables, so I consider that a success. We will discuss this lab tomorrow and review the Chapter Review problems for Newton’s 2nd Law of Motion. Then, we jump into gravity!

Physics F completed their lab investigation on static and kinetic friction. Physics G began their discussion of forces with an overview of the concept of force and the use of free-body diagrams to assess net force. Remember to account for all forces with your diagram and draw them according to the standard guidelines - tail of force vector at center of object, tip of force vector pointing in direction of force.

Homework

Honors Physics: 4B and Chapter Review #21-23 (you can remove 25 and 25 from the assignment)
Physical Science B: Gravitational Forces worksheet
Physical Science E: Complete lab write up
Physics F: Work on lab write up
Physics G: Read 4.2 and complete 4.2 section review and p. 151 #1-5