Happy π Day!!! I wish I could celebrate with you, but I don’t think you want the stomach bug
Pressure Problems • Here’s an outline as to how to work through the problems you started yesterday. • Try and finish them today or for homework if they’re not done. • Remember to bring an irregularly shaped object to class tomorrow.
P279 Practice A #1 • Fg = 50.0 N • Fwater = 36.0 N • Funknown = 41.0 N • Pobject = ? • pwater = 1.00 x 103 kg/m3 • punknown = ? • Fg – FB = Fapparent Use this equation to find Bouyant Force
P279 Practice A #1 (cont.) • Fg/FB = ρo/ρf • Use the equation above to find #1: ρobjectand #2: ρunknown. This means you’ll have to do two separate calculations: • 1) using only object and water information • 2) using only object and unknown liquid information
P279 Practice A #1 (cont.) 1) 50/14 = ρobject/1000 ρobject = 3571 = 3.571 x 103 kg/m3 The object is made of barium 2) 50/9 = 3571/ρunknown ρunknown = 642.7 = 6.427 x 102 kg/m3
Practice A • For #2, use the mass density equation to find the maximum volume and mass for something with a mass density of 1.00 x 103 (that’s when it’ll start to sink) • For #3, use Archimedes principle and the mass density equation to find the mass of the water displaced. • For #4, the buoyant force will equal the Fg since helium balloons float in air. Use the same equation as #1.
Answers to Section Review p279 • Check your answers: • A solid has a definite shape, while a fluid does not; a liquid has a definite volume, while a gas does not. • b, c, and d • 4.7 x 103 m3 • 9.92 x 102 m3 • The kayak’s effective density includes the material of and the air within the kayak and is less than water’s density.
Practice B p282 • It’s important to remember the Pressure Equation and Pascale’s Principle: • Pressure: P = F/A • Pressure = Force/Area • Pascal’s Principle • Pressure applied to a fluid in any container spreads equally throughout the container. • Check out Figure 6 – the pressure on the button is equal to the pressure on the truck lift
Practice B p282 #1 • In order to solve for #1, remember that the pressure on the lift is equal to the pressure on the button: • Fbutton/Abutton = Flift/Alift • rbutton= 5.00cm (use this to find the area of the button) • rlift = 15.0cm • Flift = 1.33 x 104 N • Fbutton = ? • Plift = ?
Practice B p282 #1 (cont) Fbutton/0.07065 = (1.33 x 104)/0.00785 Fbutton = 1.19 x 105 N Plift = (1.33 x 104)/0.00785 = 1.694 x 106 Pa
Practice B p282 • For #2: remember that pressure is exerted evenly throughout the water bed, so if you can find Fg and Area, then you can find the pressure. • For #3: the area of the eardrum stays the same, but the force and pressure change from the bottom to the top of the mountain.
Section Review p283 • Check your answers • A • 3.59 x 106 Pa • 5.0 x 106 Pa; 5.0 X 101 • 20.1 m **Pa is Pascal, which is the unit of measurement for Pressure
Don’t Forget! • The AP night is tomorrow (Thursday) at 6pm. We’ll be setting up the catapults and anything else you can think of. Try and be there by 5:45pm. • Take a book home if you need to finish anything from today.