Exam III Physics 101 Lecture 17 Fluids II

Exam III Physics 101: Lecture 17 Fluids II Exam correction today during lab time in 242 Loomis Physics 101: Lecture 17, Pg 1

Archimedes’ Principle l Determine force of fluid on immersed cube èDraw FBD l. Buoyant force is weight of displaced fluid! Physics 101: Lecture 17, Pg 2 43

Archimedes Example A cube of plastic 4. 0 cm on a side with density = 0. 8 g/cm 3 is floating in the water. When a 9 gram coin is placed on the block, how much sinks below water surface? Fb h Mg mg Physics 101: Lecture 17, Pg 3 12

Question Suppose you float a large ice-cube in a glass of water, and that after you place the ice in the glass the level of the water is at the very brim. When the ice melts, the level of the water in the glass will: 1. Go up, causing the water to spill out of the glass. 2. Go down. 3. Stay the same. Must be same! Physics 101: Lecture 17, Pg 4 14

Archimedes’ Principle l If object is floating… Physics 101: Lecture 17, Pg 5 8

Archimedes’ Principle l Which picture looks like an ice cube floating? … A B C Physics 101: Lecture 17, Pg 6 8

How much of the Iceberg can you see? Physics 101: Lecture 17, Pg 7

Where are you going to hit the Iceberg? Physics 101: Lecture 17, Pg 8

Question 2 Which weighs more: 1. A large bathtub filled to the brim with water. 2. A large bathtub filled to the brim with water with a battle-ship floating in it. Tub of water + ship 3. They will weigh the same. Tub of water Weight of ship = Buoyant force = Overflowed water Weight of displaced water Physics 101: Lecture 17, Pg 9 16

Fluid Flow Concepts r A 1 P 1 v 1 A 2 P 2 v 2 • Mass flow rate: Av (kg/s) • Volume flow rate: Av (m 3/s) • Continuity: A 1 v 1 = A 2 v 2 i. e. , mass flow rate the same everywhere e. g. , flow of river Physics 101: Lecture 17, Pg 10 21

Bernoulli’s Eq. And Work = DK + DU l W=F d = PA d = P V l. W (P 1 -P 2) V = ½ m (v 22 – v 12) + mg(y 2 -y 1) (P 1 -P 2) V = ½ V (v 22 – v 12) + Vg(y 2 -y 1) P 1+ gy 1 + ½ v 12 = P 2+ gy 2 + ½ v 22 Compare P 1, P 2 r A 1 P 1 v 1 A 2 P 2 v 2 Physics 101: Lecture 17, Pg 11 33

Example: hose A garden hose w/ inner diameter 2 cm, carries water at 2. 0 m/s. To spray your friend, you place your thumb over the nozzle giving an effective opening diameter of 0. 5 cm. What is the speed of the water exiting the hose? What is the pressure difference between inside the hose and outside? Continuity Equation Bernoulli Equation Physics 101: Lecture 17, Pg 12

Example: Lift a House Calculate the net lift on a 15 m x 15 m house when a 30 m/s wind (1. 29 kg/m 3) blows over the top. Physics 101: Lecture 17, Pg 13 48

Is Bernoulli’s Eq. involved in airfoil lift? Physics 101: Lecture 17, Pg 14

Fluid Flow Summary r A 1 P 1 v 1 A 2 P 2 v 2 • Mass flow rate: Av (kg/s) • Volume flow rate: Av (m 3/s) • Continuity: A 1 v 1 = A 2 v 2 • Bernoulli: P 1 + 1/2 v 12 + gh 1 = P 2 + 1/2 v 22 + gh 2 Physics 101: Lecture 17, Pg 15 50