No, I Don't Know When Report Cards Come Out

I'm not sure if people are enthusiastic or apprehensive about getting their quarterly marks, but believe me when I say that once my grades are turned in, report card duties are out of my hands...

Honors Physics reviewed their centripetal force lab and results varied, as expected. Most groups found good relationships between the measured centripetal force and the calculated centripetal force, but there were significant sources of error possible, depending on your setup. We then turned attention towards defining and calculating basic descriptors of circular motion – displacement, speed and acceleration – and discussed how these values were analogous to their linear counterparts. This is important to keep in mind as we move through this unit – if you get stuck trying to figure out how to calculate something, think about how you would calculate the linear variety of the property and rewrite with angular equivalents. Tomorrow, tackling tangential speed and two more accelerations!

Physical Science B and E were introduced to the concepts of work and power today and the formulas for solving problems in these areas. Remember that for work to be done by a force there has to be displacement and the force itself had to cause or act in a direction opposite the displacement. We contrasted lifting an object (work is done by your arms) with carrying an object (work is not done by your arms) and examined examples of positive and negative work. For power, make sure that you are very clear that power is the rate at which work is done/energy is transformed. Machines with different power ratings can do the same amount of work – the higher power machine just does it in less time. For problem solving, it is quite common to first have to calculate the work done on or by an object and then use that value for your power calculation. It could go even further than that – you might have to calculate distance and/or force first and then calculate work before solving for power. Just remember to work backwards – what do you need to solve for, what do you need to solve for that variable, what do you need to solve for the variables necessary for the final solution, etc. Plan your attack and if it doesn’t work, try something else until you find the correct method.

Physics F reviewed basic descriptors of rotational motion and then moved into tangential speed and acceleration. Whereas angular speed and acceleration are the same for all points on a rigidly rotating body, tangential speed and acceleration change with different points. In fact, they have to change in order to keep the angular quantities the same! We then looked at the idea of centripetal acceleration – the acceleration involved in the change of direction characteristic of circular motion. Tomorrow’s lab will allow you to measure centripetal acceleration and the force that produced it (centripetal force) and test which variables affect their magnitude.

Physics G conducted their centripetal force lab and no one received a concussion – score! By measuring period and radius of a rotating object, calculations of centripetal acceleration can be conducted. Combined with the mass of the washers, centripetal force could be established. Radius and mass were varied and their effects on centripetal force was noted and graphed. We will discuss centripetal acceleration tomorrow and also the linear quantities of tangential velocity and acceleration. Have your labs completed so that we can discuss them as part of class.

Homework

Honors Physics A: Practice 7D, practice 7E #4, Practice 7F #2,3
Physical Science B and E: Complete Practice and Section Review questions/problems on page 284
Physics F: Complete the 7.2 Section Review and p. 270 # 17,18,20
Physics G: None. We will work on the lab in class tomorrow