1. AND THEIR FORCES Fluids

2. Matter that can flow is called a fluid. “Fluid” does not mean the same thing as “liquid.” Both liquids and gases are called fluids.

3. Fluid Pressure In fluids, molecules are constantly moving in all directions As a molecule moves and collides w/ a surface, it exerts a force on that surface All of the forces exerted by the individual molecules are added together to make up the pressure exerted by the fluid. Pressure = Force / Area Pascal's Vase - demonstrating that depth, not shape, determines fluid pressure...

4. Pascal’s Principle When force is applied to a CONFINED FLUID, an increase in pressure is transmitted equally to ALL parts of the fluid.

5. Pressure = Force / Area Pressure: a force pushing on a surface Pressure = Force / area Unit of measure for Pressure is the Pascal:  1Pa = 1N/m 2 Remember 1 N = 1kg m/ sec 2

6. Air Pressure Air pressure is the result of the weight of a column of air pushing down on an area. 1 in x 1 in square column of air weighs 14.7 lbs at sea level Air exerts a balanced force when fluid is NOT moving: the pressure pushing down on your hand is balanced by the pressure pushing up on your hand

7. Variations in Fluid Pressure Elevation – the distance above sea level. As altitude increases  Air pressure decreases As air pressure decreases, so does density. As water depth increases  water pressure increases Water 800x more dense than air, so pressure increases dramatically w/ depth – every 33 ft in depth adds 1 “atmosphere “ of pressure

8. Remember… Why do some objects float in water, while others sink? Density

9. Archimedes Principle The buoyant force on an object is equal to the weight of the fluid displaced by the object. The buoyant force is opposite (pushes up) to the force of gravity (pulls down)

10. Sinking and Buoyant Force A 400 cm 3 rock sinks to the bottom of a pond. When the rock is completely underwater, it displaces (pushes aside) an amount of water that is equal to its volume. Which has its molecules more tightly packed: the rock or the displaced water?

11. Sinking and Buoyant Force On Earth, both the rock and the water exert an upward buoyant force equal to their weight. Which substance has a greater buoyant force on Earth?

13. Sinking and Buoyant Force When the rock is dropped into the water, the water’s buoyant force is not enough to support it. The rock sinks because its weight is greater than the weight of the displaced water. What are some substances that float?

14. Can Density Be Changed? Changing shape

15. Can Density Be Changed? Change Mass

16. Can Density Be Changed? Change Volume The swim bladder is filled with gases produced in a fish’s blood. The inflated swim bladder increases the fish’s volume and which decreases the fish’s overall density, and keeps the fish from sinking in the water. A fish’s nervous system controls the amount of gas in the bladder. Some fish, such as sharks, do not have a swim bladder. These fish must swim constantly to keep from sinking.

17. Bernoulli’s Principle The pressure exerted by a moving stream of a fluid is less than the pressure of the surrounding fluid. The faster the fluid moves, the less pressure it exerts on the surface of the object