Wake Up!

It's school time again, you slackers with your 4-day weekend. Bright-eyed and bushy-tailed we march onwards!

B Block conducted a lab investigation that targeted static and kinetic friction. We measured those values for a block of wood stationary on and moving across your lab table, highlighting the value for F_s,max, the way in which the graphs demonstrated equilibrium and how varying the normal force varied both of these friction measurements. With your data, you will also calculate the coefficient of friction between your surfaces. Remember - mass is not weight, so make sure you are using the object's weight to determine the normal force. Also, when you slid your block across the table and used the motion detector to measure the velocity change, it is important that the data was linear, indicating constant acceleration. Use that acceleration value (the slope of the line you recorded) in Newton's 2^nd Law of Motion formula to determine the value of kinetic friction acting on the block. Tomorrow, we'll go over the lab (though it is not due until Thursday) and the homework on friction before adding air resistance to the mix. Test now scheduled for Friday.

C, E and F Blocks had their discussion of friction and air resistance,though F Block has a tiny piece to catch tomorrow. Objects are subject to friction whenever they contact other matter, whether they are moving or not. Static friction has a larger value than kinetic friction because of the adhesive bonds that are able to form when objects are stationary against each other. Once in motion, the surface imperfections are important aspects of the surface construction to worry about We discussed how the normal force relates to the magnitude of the frictional force and how to work in those pesky surface imperfections in to an equation to evaluate friction. The coefficient of friction can be experimentally determined in lab and used to assess the value of frictional resistance an object experiences. Doesn't mean the normal force still isn't a player, though. A small car and a large truck on the same road do not experience the same force of friction, even if they have identical tires. The trucks larger weight produces a larger normal force and, so, is subject to a larger force of friction. Tomorrow, we'll tidy up loose ends for C and F Blocks, review and launch into Thursday's exam. E Block's exam is on Friday, but we have more ground to cover, so the extra day is needed.