# Spring 16 Mechanics Week 6

Day 1: Reviewing some Problems, and finishing up problem sets

Before Class: Cookies at Office Hours this week – Office Hours Listed on Main Page

• Read Chapter 6 in your text. You don’t have to read it exhaustively, but please understand where the information is. Chapter 6.2 explains centripetal acceleration. 6.3 discussion forces that produce circular motion, using the word “centripetal force”, which I find to be a damaging term. Please come prepared to ask and answer the question, “why is there no such thing as ‘centripetal force’?” 6.4 deals with other fictitious forces like “centrifugal force” and “Coriolis Force”. It is important to know what these forces are… or claim to be so that you will know not to use them.
• Watch derivation of Centripetal Acceleration and how to use it. Make sure you can do this for Big Exam.
• My response to your feedback has been posted on the main webpage
• PS#6 posted
• Question: What is the requirement on tension in order to ensure that the water stays in the bottle when it’s over your head?

In Class

• Hand in PS#5
• Questions on PS#5

After Class

• Finish video project #1 to hand in tomorrow.

Day 2: Centripetal Acceleration and the Satellite Problem

Before Class Cookies at Office Hours this week – Office Hours Listed on Main Page

Free Breakfast for bicyclists this month at different places. See the

• See video on Slack Lining.
• See video on solution for 2D inelastic collision from a problem set from years past.
• Check out the video I made for you guys about dragsters
• Finish video project #1 to be handed in today.
• My response to your feedback has been posted on the main webpage
• PS#6 posted
• PS#5 Solutions Posted
• Hey, so an important point came up today after class. For the rotating platform, we are dealing with static friction so the force of friction is less than or equal to mu*normal force (in this case mg). So if the turntable is at rest, the acceleration = zero and the frictional force = 0. As we speed it up, the acceleration increases, so the necessary force must also increase, so the frictional force on the object increases. Then at some point, the acceleration is so great that the required force is greater than the maximum static friction, and the frictional force can no longer pull the penny into the circle and it slides off in a straight line trajectory. This is much like if you were spinning a ball on a string over your head David and Goliath style. As you spin the ball faster and faster, the acceleration of the circular orbit increases and the tension in the string gets greater…. until it breaks. Then the ball continues traveling in a straight line trajectory; or actually parabolic trajectory to the ground.

In Class

• Hand in your improved video project #1.
• Big Exam! #4

After Class

Day 3: Circular Dynamics

sum of the forces = m*a, for centripetal acceleration
Take away Concept: When dealing with circular motion, dynamics is just the same as always: the vector sum of the forces = m*a. The only difference is that “a” is centripetal acceleration.

Before Class: Cookies at Office Hours this week – Office Hours Listed on Main Page

Free Breakfast for bicyclists this month at different places. See the

Where do you weigh more on a perfectly spherical world: On the equator or at the pole?

After Class

Day 4: Trigonometry! Projectile Motion; Full Kinematics in one- and two-dimensions

In Class: Cookies at Office Hours this week – Office Hours Listed on Main Page

• Use Algebra to solve one-dimensional problems – solve the “catching the bus”, or “catching the speeder” problem.
• Use trigonometry to solve projectile motion problems

Before Class

• Solutions to BE#4 posted on main webpage. Please see them. I forgot to include that the speed of the car going over the hill was 20 m/s, I’m dreadfully sorry! Please see the solutions before class and understand how to work this problem.
• From Textbook: Read chapter 2 – most of it is review, and you should skim over it. However, check out the stuff that’s new, and know where some of the other information.
• See and then you’re allowed to use those two unhelpful (in my opinion) equations, although hopefully, you’ve realized by now that you can get along without them just fine.
• Read section 3.4 on projectile motion. See how they do it and compare it to the video on projectile motion.

In Class

• Shooting the Monkey
• problem solving! PS#6

After Class Cookies at Office Hours including Friday – Office Hours Listed on Main Page