# Warm-Up Exercise for lecture 18

## Due 8:00 am, Thurs, 29 Oct 2009

Physics 105, Fall 2009

Where is the pressure greater, one meter beneath the surface of Lake Michigan or one meter beneath the surface of a swimming pool?
☐ Lake Michigan
☐ swimming pool
☑ the same

The buoyant force of a submerged object always equals:
☐ the weight of the object
☐ the net force on the object
☑ the weight of the water that would otherwise occupy the object's space

(Caution: this one requires some careful thinking.) A cannonball sits in a boat on a lake. A person then throws it overboard and the ball sinks to the bottom of the lake. Compared to when the cannonball was in the boat, will the overall water level of the lake as measured on the shore rise, fall or stay the same?
☐ rise
☑ fall
☐ stay the same

Ralph measures the pressure in his flat tire with a standard automotive pressure gauge. The gauge reads zero. Should Ralph really believe that the pressure inside the tire is zero, or should he not? Explain.
The gauge measures *differences* in pressures, not the real pressure values. To get the pressure inside the tire, you have to take the gauge pressure + atmospheric pressure. So... no, Ralph, the pressure inside is not really zero.