PHY205H1F Summer Physics of Everyday Life Class 4: Liquids & Gases

1. PHY205H1F Summer Physics of Everyday LifeClass 4: Liquids & Gases • The Atmosphere • Atmospheric Pressure • The Barometer • Boyle’s Law • Buoyancy of Air • Bernoulli’s Principle • Plasma • Pressure • Buoyancy in a Liquid • Archimedes’ Principle • What Makes an Object Sink or Float • Pascal’s Principle • Surface Tension • Capillarity

2. Atoms • Atoms are the building blocks of all matter • They are too small to be seen with visible light • One gram of water has a volume of 1 cm3 and contains more than 1023 atoms! • 1023 = • This is a scanning tunneling microscope image of graphite taken by Igor Fridman, a graduate student in U of T Physics • The dots are individual carbon [image from http://www.physics.utoronto.ca/~ifridman/ ]

3. Atomic structure is composed of: • An atomic nucleus, which contains • Orbiting • The nucleus is composed of and , which are in turn made of smaller quarks • Protons have electric charge: • Electrons have electric charge: • All atoms have the same number of protons as electrons [Image retrieved Jan.10, 2013 from http://www.safetyoffice.uwaterloo.ca/hse/radiation/rad_sealed/matter/atom_structure.htm ]

4. Atoms Check your neighbour The nucleus of an electrically neutral iron atom contains 26 protons. How many electrons are in this iron atom? • 52 • 26 • 24 • 28 • zero

5. The Elements Atoms • Refer to particles that make up a substance Elemental substance • Composed of only • Lightest and most abundant is hydrogen. • To date, about 115 elements are known. • 90 occur in nature. • Others produced in laboratory are unstable. Words and can be used interchangeably. [Image retrieved Feb.4 2013 from http://parisbreakfasts.blogspot.ca/2011/09/financiers.html ]

6. Atoms Challenge Question: Do you know it? The atomic number of an element matches the number of A. protons in the nucleus of an atom. • electrons in a neutral atom. • Both of the above. • None of the above.

7. Periodic Table of the Elements

8. Discussion question: What do you think? What is the approximate density of water? • 10−5 kg/m3 • 0.01 kg/m3 • 0.1 kg/m3 • 1 kg/m3 • 1000 kg/m3

9. Density Amount of mass per unit volume of a material. Unit of density is kg/m3 or g/cm3. Example: Density of water is kg/m3, or g/cm3. mass = Density volume [Image retrieved Jan. 11, 2013 from http://www.amazon.com/Evian-Water-Liter-Pack/dp/B0041HVMU0 ]

10. Atoms Check your neighbour If the volume of an object were to double, with no change in mass, what would happen to its density? • It would remain unchanged. • It would double. • It would decrease by a factor of two. • None of these.

11. Pressure • Pressure is the per unit that one object exerts on another • In equation form: • Depends on area over which force is distributed • Units: N/m2, or ( ) force Pressure area

12. Pressure CHECK YOUR NEIGHBOR When you stand on one foot instead of two, the force you exert on the floor is A. less. • the same. • more.

13. Pressure CHECK YOUR NEIGHBOR When you stand on one foot instead of two, the pressure you exert on the floor is A. less. • the same. • more.

14. Pressure in a Liquid • Force per unit area that a liquid exerts on an object • dependent and not dependent Example:Swim twice as deep, then twice as much weight of water above you produces twice as much pressure on you.

15. Pressure in a Liquid Effects of water pressure • Acts to surfaces of a container • Liquid spurts at right angles from a hole in the surface. • The greater the , the greater the exiting speed.

16. Buoyancy in a Liquid Buoyancy • Apparent loss of weight of a submerged object • Amount equals the weight of

17. Displacement rule: A completely submerged object always displaces a volume of liquid equal to . Example: Place a stone in a container that is brimful of water, and the amount of water overflow equals the .

18. http://www.dairygoodness.ca/butter/butter-tips-tricks/how-to-measure-butterhttp://www.dairygoodness.ca/butter/butter-tips-tricks/how-to-measure-butter • When butter is in hard, irregular shaped pieces, fill a 2-cup liquid measuring cup with water to the 1 cup mark. • Add enough butter pieces until the level reaches 1-1/4 cups. • Drain off the water and you’re left with of butter!

19. Archimedes’ Principle • Discovered by Greek scientist Archimedes in 250 BC. • Relates buoyancy to displaced liquid. • States that an immersed body (completely or partially) is buoyed up by a equal to the weight of the fluid it displaces. • Applies to gases and liquids. [ image retrieved Jan.17 2013 from http://personal.maths.surrey.ac.uk/st/H.Bruin/MMath/archimedes.html ]

20. Demonstration Prediction • A steel mass of 0.75 kg hangs from a spring scale. • When it is not accelerating, the spring scale reads 7.5 N. • If Harlow dips the mass into an open container of water, then stops the motion and lets the scale settle, what will be the reading on the scale? • Less than 7.5 N, but not zero • More than 7.5 N • About 7.5 N • zero

21. Flotation • Principle of flotation: • A floating object displaces a weight of fluid equal to its own weight. Example: A solid iron 1-ton block may displace 1/8 ton of water and sink. The same 1 ton of iron in a bowl shape displaces a greater volume of water—the greater buoyant force allows it to .

22. Ch.13 Problem 8 • Your friend of mass 100 kg can just barely float in fresh-water. Calculate her approximate volume.

23. You place an object in a container that is full to the brim with water on a scale. The object floats, but some water spills out. How does the weight of the object compare with the weight of the water displaced? A. Weight of object is greater than weight of water displaced. Weight of object is less than weight of water displaced. Weight of object is equal to weight of water displaced. There is not enough information to decide. Flotation CHECK YOUR NEIGHBOR

24. The Falkirk Wheel’s two caisson are brimful of water and the , regardless of whether there are boats in them. This makes rotation and lifting almost effortless. [image from http://en.wikipedia.org/wiki/File:FalkirkWheelSide_2004_SeanMcClean.jpg ]

25. Archimedes’ Principle Denser fluids will exert a greater buoyant force on a body than less dense fluids of the same volume. Example:Objects will float in saltwater (density = 1.03 g/cm3) than in freshwater (density = 1.00 g/cm3). [ image retrieved Jan.17, 2013 from http://famoustourisms.com/2011/05/dead-sea-enjoy-the-charm-and-sensation-swim-here/ ]

26. What Makes an Object Float or Sink? Whether an object floats or sinks depends upon the • Weight of the . • Weight of the . The weight of the fluid displaced depends on . So what really counts is the weight of the object per . This is related to the average of the object. [ image retrieved Jan.17 2013 from http://en.wikipedia.org/wiki/File:Kylpyankka.jpg ]

27. What sinks? What floats? • An object more dense than the fluid in which it is immersed will . • An object less dense than the fluid in which it is immersed will . • An object having a density equal to the density of the fluid in which it is immersed will . [ from http://www.flickriver.com/photos/rhosoi/popular-interesting/ ] [ from http://weeboopiper.wordpress.com/tag/pier-7/ ] [ from http://www.123rf.com/photo_10758041_bluefin-tuna-thunnus-thynnus-saltwater-fish-underwater-blue-sea.html ]

28. Two solid blocks of identical size are submerged in water. One block is lead and the other is aluminum. Upon which is the buoyant force greater? A. On the lead block On the aluminum block Same on both blocks There is not enough information to decide. What Makes an Object Float or Sink? CHECK YOUR NEIGHBOR

29. Pascal’s principle: • Discovered by Blaise Pascal, a scientist and theologian in the 17th century • States that a change in pressure at any point in an enclosed fluid at rest is transmitted toall points in the fluid • Applies to all —gasesand liquids

30. Pascal’s Principle • Application in hydraulic press Example: • applied to the left piston is transmitted to the right piston. • A load on small piston (left) lifts a load of on large piston (right).

31. Surface Tension The tendency of the surface of a liquid to and thus to behave like a stretched elastic membrane. [insect image from http://austincoppock.com/2012/04/astrology-42-48-surface-tension/ ] • Examples: • Insects can stand on the surface of water, even if they are more dense than water. • In a small droplet of water, the surface will contract until it forms the shape with the smallest surface area for its volume: a sphere [image from http://www.dailymail.co.uk/news/article-1371416/Photographer-Adam-Gormley-captures-ant-trapped-raindrop.html#axzz2K9hLsZGF ]

32. Surface Tension Surface tension is caused by molecular . Beneath the surface, each molecule is attracted in every direction by neighboring molecules. A molecule on the surface of a liquid is pulled only by neighbors on each side and downward from below; there is no pull . These molecular attractions tend to pull the molecule from the surface the liquid, causing surface tension.

33. Test on Wednesday during class time • Location: EX310 (last name A-M), EX320 (last name N-Z) • Test will begin promptly at 10 minutes after the hour and will be 1 hour and 50 minutes long. • Please bring a calculator, and, if you wish, a 8.5x11” aid sheet upon which you may write anything you wish on both sides • Test will cover Hewitt chapters 2-5, 7, 8, 13 and 14, and will include: • 6 short-answer problems for which you must show your reasoning • 16 multiple choice questions – you fill in a bubble sheet • Questions will be similar in style and level to the Exercises and Problems at the end of the chapters in Hewitt

34. Tips for the 2 hour Test • No phones / ipodsetc allowed. You will need a regular calculator, and a watch could be handy as well! • Time Management: • Skim over the entire test from front to back before you begin. Look for problems that you have confidence to solve first. • If you start a problem but can’t finish it, leave it, make a mark on the edge of the paper beside it, and come back to it after you have solved all the easy problems. • Bring your T-card or other photo ID, as we will be collecting signatures

35. PHY205 Physics of Everyday LifeChapter 14: Gases • The Atmosphere • Atmospheric Pressure • The Barometer • Boyle’s Law • Buoyancy of Air • Bernoulli’s Principle • Plasma [image from http://blog.testfreaks.com/information/thq-and-disney-pixars-up-the-videogame-preview/ ]

36. Atmospheric Pressure The global average sea-level pressure is Pa, or 1 atm.

37. Atmospheric Pressure in this room What is the force of air pressure on the top of your outstretched hand? Atmospheric Pressure: 20 square inches = pounds! Why don’t you feel that force pushing your hand down? What if all the air below your hand was removed (a vacuum)?

38. Discussion Question • A suction cup sticks to a wall. It is • pulled to the wall by the vacuum. • pushed to the wall by the atmosphere. • both of these • neither of these [image from http://www.flippersandfins.net/bettabreedingarticle.htm ]

39. Pressure and “Suction” A fluid can only walls or objects; a fluid cannot pull on a wall. What we call “suction” is when the fluid on one side has a higher pressure than the fluid on the other side. It is the pressure which creates a pushing force into the lower pressure area (into the vacuum). This is how we breath: We expand our lung cavity, lowering the inside. The higher air pressure outside air into our lungs.

40. Atmospheric Pressure CHECK YOUR NEIGHBOR In drinking soda or water through a straw, we make use of • capillary action. • surface tension. • atmospheric pressure. • Bernoulli's principle. • none of these

41. Atmospheric Pressure • Pressure at the of a column of air reaching to the top of the atmosphere is the same as the pressure at the of a column of water m high. • Consequence: The highest the atmosphere can push water up into a pump is 10.3 m. • Mechanical pumps that don’t depend on atmospheric pressure don’t have the 10.3-m limit.

42. The Barometer • The barometer is a device to measure . • It consists of a tube upside down in a dish filled with mercury. • The height of the mercury column tells us the atmospheric pressure. • Atmospheric pressure decreases with increasing altitude, so it also measures —an altimeter.

43. Why don’t barometers use water instead of mercury? A. Water cannot be used because it does not exert pressure. Water cannot be used because it sticks to the glass. Water can be used but the barometer will be too tall. None of the above. Barometer CHECK YOUR NEIGHBOR

44. Boyle’s Law The product of pressure and volume of a given mass of gas will always remain the same. = LARGEPressure LARGEVolume SmallPressure SmallVolume

45. Discussion Question • When a party balloon is compressed to one-third its volume with no change in temperature, what happens to the gas pressure in the balloon? • It drops by a factor of 3 • It drops by a factor of 2 • It remains the same • It doubles • It triples

46. Buoyancy in Air Archimedes’ principle applies to as well as liquids. • An object surrounded by is buoyed up by a force equal to the weight of the displaced [image downloaded Jan.24 2013 from http://saigon-hobby.com/products/2739-air-swimmer-nemo.aspx ]

47. Buoyancy Example: If you wish to support a mass of 80 kg (one person) with a helium-filled balloon, how big should the balloon be?

48. In-class Discussion Question • You put your thumb over the end of the a hose, thereby reducing the area through which water can exit the hose. • What must change about the water so that the amount coming in the hose equals the amount leaving the hose? • The velocity must increase. • The velocity must decrease. • The pressure must increase. • The pressure must decrease.

49. In-class Discussion Question • We study the steady flow of water from a water tap, e.g., in your kitchen sink. The jet of water • broadens as it falls. • narrows as it falls. • does not change its cross-sectional shape. • slows before hitting the bottom of the sink.

50. Bernoulli’s Law • Consider an ideal fluid, flowing through a tube which narrows. • It increases its . This means the kinetic energy per volume of the fluid will . • How can this be? There must be a which does work on the fluid to speed it up. • The force must come from a difference. • Pressure must be in the region of increased fluid velocity.