# Warm-Up Exercise for lecture 12

## Due 8:00 am, Tues, 8 Oct 2009

Physics 105, Fall 2009

Which has greater linear speed, a horse near the outside rail of a merry-go-round or a horse near the inside rail?
☑ outside horse
☐ inside horse
☐ both the same

Which has greater angular speed, a horse near the outside rail of a merry-go-round or a horse near the inside rail?
☐ outside horse
☐ inside horse
☑ both the same

A ladybug sits on the outer edge of a merry-go-round that is turning around counter-clockwise without speeding up or slowing down. In what direction is the friction force sticking the ladybug to the merry-go-round?
☐ clockwise
☐ counter-clockwise
☑ inward
☐ outward

Ralph is confused about centripetal and centrifugal forces. When he is in a car which is turning to the left, he feels a force pushing him to the right. But the textbook says that the actual force is pushing him to the left. Can you explain this to him? What is he feeling during the turn? (Please: no more of the "Tell Ralph to stop asking questions" or "Tell Ralph to ask Dr Colton" answers. They were funny at first, but now that I'm getting ~50 of them for each warmup, it has kind of gotten old. Just give it your best shot at a real explanation, or leave it blank. Or write some *other* funny comment. ;-) Thanks.)
Centripetal: as viewed from a stationary (or constant velocity) frame of reference, it's clear the force must be to the left--otherwise Ralph would continue moving straight forward! Centrifugal: as viewed from the accelerating frame of reference, inside the car, it does feel like some mysterious force is pushing Ralph to the right. This is what we call a "fictitious force" and is a result of Ralph's own inertia.