Rolling into the Long Weekend

At least you guys don't have to come in tomorrow - pity the poor teachers who have to sit through meetings and work on curriculum. Yeah, plotting and planning new ways to make you miserable...

B Block got into a deep discussion about friction, both kinetic and static and the concept of the coefficient of friction. Friction jumps up every time matter contacts matter, but the magnitude depends on several things including the nature of the surfaces and the normal force that acts on the object. Static friction always has a larger value for a given situation than kinetic friction and Tuesday's lab will let you explore that in detail. For your homework problems - they're not hard per se, but they tend to require a number of steps to accomplish. Take your time, sketch things out, watch for applied forces being implemented at an angle and consider how that affects the normal force, frictional resistance and net force acting on the object. We'll go over these on Wednesday before touching on air resistance.

C Block conducted a lab on static and kinetic friction and saw clearly how force applied to an object does not necessarily make an object move. You must exceed the maximum amount of static friction the system can produce before motion can occur. Up until that point the value for applied force is balanced by the static friction, so the object stays in equilibrium. Once F_s,max has been exceeded, the object begins moving, but is still subject to kinetic friction. From your data you will be calculating the frictional force acting on your blocks, the coefficient of friction between the block and reflecting on the nature of forces in motion as you move through the analysis questions and write-up. The lab isn't due until Wednesday, so be prepared on Tuesday to ask me any questions you might have about the lab. We'll go over it in a general way, but you need to tell me if you need specific help with a question or calculation.

E Block took up the ideas of weight and the normal force, which will propel us into a discussion of friction on Tuesday. Remember that the magnitudes of weight and the normal force are only equal if the object is on a flat, horizontal surface. Otherwise, F_Nis only a component of the object's weight. Also, the normal force is affected by applied forces if they act in or have a component that acts perpendicular to the surface. Keep an eye out for those problems and don't forget to add of subtract that value into your calculations. On Tuesday, we'll take up a discussion of friction and you will need to work with both weight and the normal force to successfully manage situations where we include frictional resistance.

F Block started the period by going over Newton's 3rd Law of Motion. When one object contacts another, two forces are immediately and simultaneously generated, equal in magnitude and opposite in direction to each other. To determine the behavior of the objects after the contact, you have to bring those forces into Newton's 2nd Law of Motion and, with the objects' inertia, calculate the resulting acceleration on each object. We then looked at weight, which is easy to confuse with mass, but is something very different. Mass is an inherent property of matter, but weight varies with location since acceleration due to gravity is location-dependent. Weight is a force, reported in Newtons, so make sure that mass is in kilograms and acceleration is in m/s² when you calculate an object's weight. On Tuesday, we'll tackle the normal force and might dip toes into the area of friction.

Have a great long weekend!