Honors Physics 1 Class 09 Fall 2013 Quiz 4 Line integrals Potential Energy

So what?

Line integrals Requires force vector, path (in vector form), dot product and integral. Sometimes you can do several separate integrals over simple steps in the path. Sometimes you need to relate dx, dy, dz in the path. Examples follow.

Work by a uniform force

Work done by what on what? Be careful when evaluating work. Is it not unusual to focus on one force (the force you apply and neglect others.) Consider lifting a book from the floor to the table. You do work FyouH so Wby you = FyouH. But gravity does work too=-FyouH. Total work = 0.

Bad force!

Bad force with functional path

Conservative forces and Potential Energy If the work line integral between two points is independent of the path taken, then the force is conservative.

Work and potential energy Dang! Notes 6 PHYS1100_F2012

Exercise 9.1_______________ Skateboarder Going Up a Ramp A skateboarder is moving at velocity v and comes to a ramp at angle theta to the ground. How high does he get? (Physically.) On what properties of the system does his height depend? (His mass? The angle? His velocity?) How long does the ramp have to be so that he doesn’t fall off the end? Notes 6 PHYS1100_F2012

Example Projectile Problem Skateboarder Going Up a Ramp Dude! Notes 6 PHYS1100_F2012

Example Projectile Problem Skateboarder Going Up a Ramp Dang! Notes 6 PHYS1100_F2012

Dang! Notes 6 PHYS1100_F2012

What potential energy tells us about force