Physical Science II

1. Physical Science II Fluid Physics

2. Fluids • Question: • What are the three common states of matter?

3. Fluids • Three common states of matter: (1) Solid (2) Liquid (3) Gas • Thus far, we have focused primarily on solids. In this unit, we will be investigating the physics of liquids and gases…

4. Fluids • Fluid – a nonsolid state of matter in which the atoms or molecules are free to move past each other—includes both liquids and gases: • Solids have a definite volume and shape. • Liquids have a definite volume but not a definite shape—take the shape of the container they are placed in • Gases do not have a definite volume or shape—spread out when placed in a larger container

5. Pressure

6. Pressure • Which is more comfortable to sit on? • A recliner or a bicycle seat • The recliner is obviously the more comfortable choice, but why? • The recliner is more comfortable because it reduces the pressure acting on your body.

7. Pressure • Pressure – the force per unit area acting on a surface: • In terms of the bicycle seat and the recliner, the recliner is more comfortable because it has a larger surface area. • The larger surface area causes the pressure to be lower.

8. Pressure • Pressure is measured in Pascals (Pa), where 1 Pa = 1 N/m2

9. Pressure • Question • What do you feel when you dive to the bottom of a deep pool?

10. Pressure • As you travel deeper in a fluid, the pressure increases. • The only two factors that determine pressure in a fluid are depth and the type of fluid. • For example: • If we climb to 3000 feet above sea level, we don’t notice the change in air pressure. • If you dive only 8 feet below the surface of water you notice a much larger pressure acting on your body.

11. Air Pressure • We live at the bottom of a vast quantity of air. • The Earth’s atmosphere, what we call air, is made up of many different types of gasses. • The air pressure at sea level is approximately 100,000 Pascals. • Just as pressure increases with depth under water, the same is true of air pressure.

12. Air Pressure • If you’ve ever felt your ears pop while driving up a mountain or flying in a plane you’ve experienced your bodies reaction to a change in air pressure. • You may be surprised to hear that right now there are 1000N of force pushing down on your head from the atmosphere. • The only reason you survive this pressure is because your body is exerting it’s own pressure against the atmosphere.

13. Air Pressure • Air pressure is measured with an instrument known as a barometer. • The barometer is a device commonly used by meteorologists to help determine the weather forecast. • A rising barometer usually indicates clear weather with low humidity. • A falling barometer indicates the approach of a storm system.

14. Pascal’s Principle • Pascal’s Principle –a pressure applied to a fluid in a closed container is transmitted equally to every point of the fluid and to the walls of the container: • Example 1 – When air is added to a tire, the pressure increases at all points inside the tire by the exact same amount.

15. Pascal’s Principle • Example 2 – In a hydraulic lift, when a small force F1 is applied to a small piston of area A1, a larger force F2 is transmitted to a larger piston of area A2: Thus, if A2is greater than A1, then F2is greater than F1!

16. Pascal’s Principle • Hydraulic lifts operate by utilizing Pascal’s Principle. • In an auto body shop, hydraulic lifts allow vehicles to be elevated in order to be inspected and repaired. • Large construction vehicles use hydraulics to operate shovels.

17. Pascal’s Principle

18. Pascal’s Principle • The advantage of hydraulics is the ability to move large forces by only exerting a small force. • This is exactly like the operation of a simple machine. • Like a simple machine, if you increase your output force, you will also decrease the output distance.

19. Buoyancy • Have you ever stood in a pool and tried lifting a friend while submerged in the water? • If you have, you probably noticed how easy it was to lift your friend. • So, why is lifting your friend easier in the pool?

20. Buoyancy • Buoyant Force – an upward force that acts on an object in a fluid. • Every object in a fluid experiences a buoyant force. • When you and your friend are in a pool, the buoyant force from the pool water acts against the gravitational force on your bodies, • This makes it seem as if you and your friend weigh less.

21. Buoyancy • Apparent Weight – in a fluid your apparent weight is equal to your actual weight minus the buoyant force. • There are several methods to find the buoyant force acting on an object, but the most important came from a Greek mathematician named Archimedes.

22. Archimedes’ Principle • Archimedes discovered an important property of buoyancy. • If you make the mistake of filling a bathtub too high, the water is going to overflow when you get into the tub. • The reason for this is because water is displaced to make room for your body to fit in the tub.

23. Archimedes’ Principle • Archimedes’ Principle – the buoyant force on an object is equal to the weight of the fluid that is displaced by that object. • To measure the buoyant force you can collect the water that is displaced by an object and measure the weight of that water. • The weight of the water is equal to the buoyant force.

24. Density and Buoyancy • Whether or not an object will float is based on density. • If an object is more dense than the liquid it is placed in, it will sink. • If an object is less dense than the liquid it is placed in, it will float.

25. Density and Buoyancy • The buoyant force acting on a floating object is exactly equal to the weight of that object. • Floating objects have an apparent weight of zero Newtons. • Also, since the buoyant force is equal to the weight of water displaced, floating objects must displace an amount of water that weighs as much as the object.

26. Density and Buoyancy • Examples: • When a 1500 N boat is floating in water, it is displacing 1500 N of that water. • If a 500 N person is floating in a pool, they are displacing 500 N of water.

27. Flight

28. Principles of Flight • In some of the earliest records of human history, studies of flight have been discovered. • The ancient Greeks studied birds in great detail and the Italian inventor Leonardo Da Vinci designed several flying machines. • For centuries humans had been attempting to fly with all sorts of wild creations, but it was the Wright brothers who eventually succeeded in controlled flight.

29. Principles of Flight • Since the Wright brothers’ historic flight there have been many advancements in the design of aircraft. • However, all flight is based on a series of physics principles.

30. Principles of Flight • Flight is possible because it occurs within the atmosphere of the Earth. • Earth’s atmosphere is a fluid that is made up of several different types of gasses most notably, nitrogen, oxygen and carbon dioxide. • The ability to fly through this fluid is based on four forces: • Lift, Thrust, Drag and Weight

31. Lift • One of the most important aspects of flight is lift. • Lift – the upward force acting on an airplane. • The cause of lift is a difference in air pressure on the top and bottom of the wing, which is explained by Bernoulli’s Principle. • Bernoulli’s Principle explains that when the speed of a fluid increases, the pressure within the fluid decreases.

32. Lift • The wing of an airplane is shaped so that the air moving over the top of the wing travels faster than the air moving around the bottom of the wing. • A lower pressure is created on top of the wing by the faster moving air. • The higher air pressure on the bottom of the wing provides the upward force that lifts the airplane.

33. Thrust • While lift allows the airplane to get off the ground, it would not exist without any thrust. • In order for lift to be generated, the air must be moving around the wing at a high velocity. • The engines of the airplane provide the force that pushes it to speeds that are great enough to generate the lift.

34. Thrust • Thrust is the force that is provided by the engines to move the airplane. • In order for the plane to get off the ground, the engines must provide enough thrust to move the air around the wings with enough speed to generate lift. • As long as the thrust is strong enough, the airplane will experience lift.

35. Drag • It is important to remember that air is made up of many different molecules and therefore it creates friction. • Air resistance is the friction that is created by the Earth’s atmosphere. • In terms of flight, air resistance produces an effect called drag. • Drag is simply the force of the air resistance that is acting against the forward motion of an airplane.

36. Drag • The drag forces that act against the motion of an airplane reduce fuel efficiency. • The more drag there is, the less efficient the aircraft.

37. Weight • The last of the forces involved in flying is weight. • Remember that weight is the force of gravity that is acting on an object. • In order for an airplane to get off the ground and to stay in flight, the lifting force must overcome the weight of the plane.

38. Forces of Flight • All in all, the success of flight is dependent on all four forces acting together. • If thrust and drag are equal, the plane will move at a constant speed. • If weight and lift are equal, the plane will fly at a constant altitude.