Conceptual Physics Alive: Scaling, Liquids, Gases
Paul Hewitt teaches about Scaling, Liquids and Gases.
Master teacher Paul Hewitt teaches non-computational Conceptual Physics. Observe Hewitt teach in a classroom with real students, using engaging demonstrations and artwork.
DVD Includes 4 Episodes:
- Episode 1: Scaling: Surface area and volume are distinguished with simple demonstrations. Several examples are used to illustrate the proportional changes in surface area and volume when objects are scaled up or down in size. Segment length: 39 minutes
- Episode 2: Liquids I: The concepts of density, pressure, and the depth-dependence of liquid pressure are used to develop the concept of buoyancy. A variety of demonstrations are used to distinguish between the displacement, volume, weight, and density of immersed objects, and to illustrate Archimede's principle. Segment length: 39 minutes
- Episode 3: Liquids II: This tape expands on the discussion of Archimede's principle in the Liquid's I tape, with an emphasis on the law of flotation. A variety of demonstrations help to illustrate these concepts. Segment length: 38 minutes
- Episode 4: Gases: This demonstration-oriented lecture focuses on the atmosphere--its weight, pressure, and the buoyancy it exerts on objects. Barometer, Boyle's Law, and Bernoulli's principle are also discussed. Segment length: 40 minutes
• Hewitt distinguishes area and volume by demonstrating the pouring of water from a spherical shaped container to a cylindrical one.
• Strength of ants, and strength of scaled-up ants compared.
• Strength of scaled-up ant compared to strength of an elephant.
• Scaling up a cube to twice size.
• Demo of eight blocks compared to one block.
• Cross-sectional area defined.
• Comparison of sketches of skeletons of cat and an elephant.
• Sag of toothpick and log compared.
• In scaling up things, the volume goes up as cube of the increase.
• Total area compared to cross-sectional area.
• Ratio of total area to volume compared for scaled-up cubes.
• Little things have more skin compared to volume than big things.
• Examples of the consequences of more surface area per volume: Cooking French fries and meatballs Breathing of insects through their skins Intestines Cells and cell division Little people versus big people in cold and hot weather Diets of mice, shrews, tiny birds versus elephants Big ears of elephants Chewing food Falling of small versus big things.
• Demonstration of terminal velocity with falling coffee filters.
• Resistance of fall is proportional to square of falling speed.
• Demonstration of dropping two Styrofoam balls, one twice the diameter of the other. [They don't fall as the coffee filters because they didn't reach their terminal velocities.]
• Demonstration of dropping two plastic balls, one twice the diameter of the other, in water. [The demo shows that fluid resistance varies as the square of the falling speed of both the filters in air and the balls in water. Assisted by Ted Brattstrom.]
• Examples of the faster speeds of big fish and big swimmers compared to their smaller counterparts.
Liquids I includes:
• The lecture begins with a comparison of the weights and densities of a Styrofoam and lead ball.
• Density defined.
• Hewitt places Styrofoam and metal balls in the hands of two students and asks which has the greater weight. Both say the metal.
• Hewitt demonstrates with a scale that the Styrofoam weighs more. The reason, having to do with pressure is discussed.
• The force of a book against the table is compared with the pressure of the same book against the table, in different positions.
• Pressure defined.
• Equation for liquid pressure is derived.
• Demonstration of Pascal's vases, wide and narrow.
• Dam designs are discussed.
• Examples of blood pressure illustrate liquid pressure.
• Buoyant force concept is introduced.
• Demonstration of buoyant force; suspending a metal cylinder in water while weighing it.
• Demonstration of displacement with an overflow can.
• Demonstration of Archimedes' principle.
• Examples to distinguish pressure and buoyancy. Examples of buoyancy with imaginary blocks.
• Flotation demonstrated.
Next-Time Question: Which floats lower in the water, a ship loaded with Styrofoam or the same ship empty? [The loaded ship (with any cargo!) will float lower in the water.]
Liquids II includes:
• Hewitt begins with review questions about Archimedes' Principle.
• Demonstration of equal volumes of iron and wood in water.
• Buoyant force related to volume of water displaced.
• Demonstration of clay sinking in water, then refashioned like a boat to float.
• The law of flotation.
• The role of density on flotation.
• Variable density of fish.
• Examples of the principle of flotation.
• Proposed Saturday night project in bathtub.
• Why a snorkel won't work below 1-meter depth.
• Life preservers.
• Distinction between net force and buoyant force.
• Floating on the Great Salt Lake (or water of high density)
• Demonstration of a block of wood floating in water, with a series of stimulating questions.
Next-Time Question 1: Consider a boat loaded with metal floating in a small container. When the metal is taken from the boat and thrown overboard into the water. Will the level at the side of the container go up, down, or remain the same? (The water level falls. because the submerged iron displaces only its volume when submerged. When it is made to float in the boat, it displaces its weight. Because iron is denser than water, its weight will be greater than the weight of an equal volume of water - the amount displaced when it is simply submerged.)
Next-Time Question 2: Consider a balloon floating in the water with a suspended weight to make it just barely float. If you push the balloon beneath the surface and let go, will it return to the surface, stay where it is, or sink? (It will sink because at the deeper level it is squashed by the greater pressure. This makes it more dense than it was, and it therefore sinks. Interesting enough, as it sinks, it will become further squashed and its density will increase further with increased depth.)
• Hewitt demonstrates what happens when an inverted glass is pushed into a container of colored water.
• The weight of air, and interesting comparisons.
• Chalkboard sketch of the world and atmosphere, and how air pressure is due to the weight of air.
• Demonstration of the crushing by the atmosphere of soft drink aluminum cans (first heated with a bit of water in them) inverted one by one into a bath of cool water.
• Atmospheric pressure.
• Data on atmospheric pressure with altitude.
• Demonstration of the burning of a piece of paper in a Jar. Hewitt puts the jar on his forehead and it sticks.
• Demonstration of atmospheric pressure with a toilet plunger.
• Demonstration of atmospheric pressure with a sheet of rubber.
• Demonstration of a filled glass of water covered with a piece of cardboard and held above the head.
• Mercury barometer explained.
• Demonstration of air poured from one container to another beneath the surface of water.
• Explanation of caissons tor underwater construction.
• Boyle's law.
• Review of the weighted balloon that barely floats (from the previous lecture).
• Snorkeling and scuba diving.
• Bernoulli's principle.
• Demonstration of various balls suspended in air by an air stream.
• Airplane lift.