Forces in Fluids 7 th Grade Science Mrs. Estevez

Fluids A fluid is any material that can flow and takes the shape of its container. A fluid is any material that can flow and takes the shape of its container. Fluids include liquids and gases. Fluids include liquids and gases.

Fluids and Pressure Pressure is the amount of force exerted on a given area. Pressure is the amount of force exerted on a given area. Pressure can be calculated by: Pressure can be calculated by: Pressure = Force Pressure = Force Area Area The SI unit for pressure is the pascal.(Pa) The SI unit for pressure is the pascal.(Pa) One pascal is the force of one newton exerted over an area of one square meter. One pascal is the force of one newton exerted over an area of one square meter.

Math Break (pg.62) Find the pressure exerted by a 3,000N crate with an area of 2m 2. Find the pressure exerted by a 3,000N crate with an area of 2m 2. Pressure = 3,000N = 1,500Pa Pressure = 3,000N = 1,500Pa 2m 2 2m 2 Find the pressure exerted by air 736N in a room 8m 2. Find the pressure exerted by air 736N in a room 8m 2.

Square Bubbles? Bubbles are round because the fluids exert pressure evenly in all directions. Bubbles are round because the fluids exert pressure evenly in all directions.

Atmospheric Pressure The pressure caused by the weight of the atmosphere. The pressure caused by the weight of the atmosphere. Atmosphere is held in place by gravity Atmosphere is held in place by gravity The layer extend 150 km above the surface. The layer extend 150 km above the surface.

Atmospheric Pressure

Atmospheric pressure varies because of the depth of the atmosphere at different points. Atmospheric pressure varies because of the depth of the atmosphere at different points. At the top of the atmosphere pressure decreases. At the top of the atmosphere pressure decreases. Pressure depends on depth. Pressure depends on depth.

Water Pressure Water is a fluid. Water is a fluid. Exerts pressure like air. Exerts pressure like air. Water pressure increases with depth Water pressure increases with depth

Water Pressure Water is 1,000 times more dense than air. Water is 1,000 times more dense than air. A certain volume of water has more mass than the same volume of air. A certain volume of water has more mass than the same volume of air. Reminder: Reminder: Density = mass Density = mass volume volume

Fluids Flow Fluids flow from high pressure to low pressure. Fluids flow from high pressure to low pressure. How does this help you use a straw or even breath in air? How does this help you use a straw or even breath in air?

The "Avatar" director is finding locations for the movie's sequel, which is to be set in the oceans of the movie's fictional planet, Pandora. He has already commissioned a made from high-tech composite materials and powered by electric motors. Cameron's sub needs to be able to survive the enormously powerful water pressure present miles below the ocean's surface. The "Avatar" director is finding locations for the movie's sequel, which is to be set in the oceans of the movie's fictional planet, Pandora. He has already commissioned a submarine made from high-tech composite materials and powered by electric motors. Cameron's sub needs to be able to survive the enormously powerful water pressure present miles below the ocean's surface.

Pascal’s Principal This principle states that a change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of that fluid. This principle states that a change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of that fluid. –Example: Car Brakes can stop large moving objects. When a driver exerts pressure on a brake petal, the pressure is transmitted to all the parts of the liquid- filled brake system. The liquid moves against the brake pads, the brake pads press against the wheels, and friction stops the car.

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Quiz 1. What do liquids and gases have in common? 2.Why does pressure increase with depth? 3. What will happen to the pressure in all parts of an enclosed fluid if there is an increase in pressure in one part?

Buoyant Force – Archimedes’ Principle The principle that states that the buoyant force on an object in a fluid is an upward force equal to the weight of the volume of the fluid that the object displaces. The principle that states that the buoyant force on an object in a fluid is an upward force equal to the weight of the volume of the fluid that the object displaces. What is buoyant force? The upward force that keeps the object immersed in or floating in a liquid. What is buoyant force? The upward force that keeps the object immersed in or floating in a liquid.

Why does a rock sink in water? Why does a rock sink in water? –A rock is more dense than water; therefore, it displaces (pushes the fluid away) the water around it. The volume of the water that has been displaced has to go somewhere else. Where? Why does a fish float in the water? Not because it is dead! Why does a fish float in the water? Not because it is dead! –When a fish displaces a certain volume of water, its weight is now equal to the buoyant force of the water. Now it can float in the water. Why do ducks buoy up in the water? Why do ducks buoy up in the water? –When the buoyant force on a duck is greater than the duck’s weight, it is “buoyed up” (pushed up) in the water. The part of the duck that is underwater displaces the amount of water that is equal to the duck’s weight.

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Can Archimedes's Principle also refer to air and density? Of course! If there is a gas that is less dense than air, it could float on top of the air. Can you think if a gas that is less dense than air? Of course! If there is a gas that is less dense than air, it could float on top of the air. Can you think if a gas that is less dense than air? Helium Helium and and Hydrogen Hydrogen

If steel is denser than water, how can it float? Changing Shape- Changing Shape- –Hollow ships are less dense than a block of steel because density is mass per unit volume. Changing Mass- Changing Mass- –Submarines have ballast tanks that can let water in to increase its mass so the submarine can sink. Those tanks can also release water to decrease mass and let the submarine “buoy up”. The volume of the submarine does not change, just the mass. Changing Volume- Changing Volume- –A fish can fill its swim bladder to increase and decrease its volume with air, making it sink and float in the water.

Bernoulli’s Principle The principle that states that the pressure in a fluid decreases as the fluid’s velocity increases. The principle that states that the pressure in a fluid decreases as the fluid’s velocity increases. The speed of a moving fluid increases, the pressure decreases. The speed of a moving fluid increases, the pressure decreases. cmEOjs4 cmEOjs4 cmEOjs4 cmEOjs4

Straws Place a straw up right in a glass of water. Place a straw up right in a glass of water. Hold a second straw a right angle at the top of the first straw. Hold a second straw a right angle at the top of the first straw. Blow very hard through the second straw. Blow very hard through the second straw. What happens? Why? What happens? Why?

Bernoulli’s Principle and Flight According to Bernoulli, fast moving air above the wing exerts less pressure than slow moving air below the wing. Lift- since there is greater pressure below the wing, this upward force (lift) pushes the wings upward against the pull of gravity. Thrust- since the amount of lift is determined by the speed at which the air travels, this forward force (thrust) is produced by a plane’s engines. Drag- this irregular of unpredictable flow of fluids/air opposes the direction of the aircraft, causing a decrease in forward motion. In airplanes, this is otherwise known a turbulence.