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Fluids pretest. Mark a F or NF for fluids (F) or Not fluids (NF) Water Copper blood Grape juice Air Iron Gum Helium Ice Rubber . Fluids. Ch 3-2. Fluids. If it can flow it is a fluid. Buoyant force. The upward force that fluids exerts on a substance
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Fluids pretest • Mark a F or NF for fluids (F) or Not fluids (NF) • Water • Copper • blood • Grape juice • Air • Iron • Gum • Helium • Ice • Rubber
Fluids Ch 3-2
Fluids • If it can flow it is a fluid
Buoyant force • The upward force that fluids exerts on a substance • Pressure tries to equalize itself, think of a balloon This force is Pressure = the amount of force exerted on a given area
Pressure = Units are called pascal = N/m2
How does a boat float? This area is below water so the density of the water displaced is more than the ship’s density See how there are no water force arrows above the boat? This is what makes a buoyant force
Pascal’s principle • A change in pressure at any point in a closed fluid will be equally transmitted to all parts of the fluid • More simply said p1 = p2 SO… Remember pressure is force divided by area
Fluids apply pressure on all sides of an object, the left and the right equal out, the bottom applies greater pressure upward than the top pressure downward because pressure increases with depth • Explain how difference in fluid pressure create buoyant force on an object? Sub Deeper water has greater pressure!
Practice problem • A hydraulic lift is used to lift a 19,000 N truck. If the area of the small piston is 10.5 cm2and the area of the larger piston is 400 cm2, what force needs to be exerted on the small piston to lift the truck Solution: = Force = 500 N
Practice problem • In a car’s liquid filled hydraulic braking system, the master cylinder has an area of 0.5 cm2 and the wheel cylinders each have an area of 3.0 cm2. If a force of 150 N is applied to the master cylinder by the brake pedal, what force does each wheel cylinder exert on the brake pad? Master cylinder 0.5 cm2 150 N Wheel cylinder 3.0 cm2 ? N
Fluids in Motion • Viscosity – a liquid’s resistance to flow • Higher viscosity means slower flowing
Fluid Pressure and speed • As fluid speed increases, pressure decreases • As space decreases speed increases • Think of a garden hose open and with your thumb over the end. • This is Bernoulli’s principle
Practice • Two boats sailing down a river are side by side with only a narrow space between them. • What happens to the fluid speed between the two boats? • What happens to the pressure? • Is it likely that the boats might collide? WHY
How can I find the buoyant force? • It is equal to the weight of the fluid displaced by the object.