Upcoming Deadlines Sixth Homework (Stop-motion Animation) Due Thursday, October 6 th (Next week) 20 points (if late, 10 points) Bonus prize of 20 extra points to top three. Seventh Homework (Outline of First Term Paper) Due Thursday, October 13 th (In two weeks) 10 points (5 points if late) For full schedule, visit course website: ArtPhysics123.pbworks.com Pick up a clicker, find the right channel, and enter Student ID

Homework Assignment #6 In this assignment you will create a stop- motion animation of a falling object. It can be a simple as a ball bounce cycle or (preferably) something more interesting, like a flour sack or a water balloon. Because you will have to pose your object at different heights, you'll either need to suspend it from a string or have the motion occur on the ground with the camera positioned directly overhead.

Homework Assignment #6 If you have a webcam, an easy way to film a stop-motion animation is to use SAM Animation ( It's free software that runs on both Macs and PCs; it was developed at Tufts University as part of a National Science Foundation project for teaching using animation. The software is designed so that it can be used by even elementary school children so you shouldn't have much trouble figuring it out.

Demo of SAM Software

Homework Assignment #6 While I encourage you to help each other out, for this assignment each person needs to create their own animation. Finally, describe in a brief paragraph how you created your animation. Post your animation clip to your blog in an entry entitled "Stop Motion Animation of Falling.“ Due by 8am on Thursday, October 6 th. 20 points (if late, 10 points) The top three animation clips in the class will receive a bonus of 20 extra points.

A very simple example

Survey Question You have some experience with creating stop-motion animation. True or False?

Thought Question A falling ball is acted on by air resistance and gravity, as shown. What is the total force acting on the ball? a.5 pounds upwards b.5 pounds downwards c.3 pounds upwards d.3 pounds downwards e.zero 1 lb. 4 lb.

Thought Question The ball has reached terminal velocity: True or False? 1 lb. 4 lb.

Stunt Bunny

Stunt Governor

Demo: Boyle’s Law The pressure in a gas increases when the gas is compressed. When a gas expands, the pressure decreases. Compress the gas by pushing in the syringe. Dial gauge shows increase in pressure. Syringe Gauge Tank

Breathing & Boyle’s Law L A A H

Pressure & Air Resistance L H Force of air resistance is due to a difference in pressure. High pressure builds by compression in front of a falling object while low pressure is created in the wake. HIGH PRESSURE LOW PRESSURE

Ground-effect Cushion Flat sheet sliding over a smooth surface compresses the air beneath it and forms a low-friction cushion, allowing it to slide. This ground-effect won’t occur with an irregular leaf or with a rough surface. Moving this way HIGH PRESSURE LOW PRESSURE L H H L

Sailing Ships L The wind blowing on a sail also produces a pressure difference, creating the force that moves the ship. H Wind

Buoyancy L The buoyant force pushing submerged objects upward is also due to a pressure difference. H

Prairie Dog Vacuum Prairie dogs captured by giant vacuum truck with a padded bin.

The Curse of the Were-Rabbit (2005)

Vacuum Cleaner Force L A Force As with any vacuum cleaner, it’s the difference of pressure that creates the net force pushing objects towards the low pressure side. Truck A

Parallelogram rule Vector Addition of Forces Two forces pulling an object are equivalent to a single total force. Object Force A Force B Net Force A + B

Sliding Sideways If leaf/paper is tilted then it slides sideways. Air Pressure Force Gravity Slides this way Picks up speed (slows out) as it slides down, as if it were sliding down an incline.

Timing and Spacing, Up & Down When the leaf/paper slides downward, it picks up speed (slows out). * With no wind Imagine riding a roller coaster. When it rises due to lift* it loses speed (slows in).

Roller Coaster Timing

Aerodynamic Lift If airflow is faster over one side than the other then a pressure difference develops, creating aerodynamic lift. Wing Moving this way Lift

Aerodynamic Lift If leaf/paper is tilted relative to its path of action then there is also an aerodynamic lift. Air Resistance Gravity Moving this way Lift Also get lift if leaf/paper is curled like a wing.

Effect of Lift Path of action deflected by lift. Lift No Lift Lift force can also deflect the path of action downward, depending on the tilt angle of the leaf/paper. Lift requires tilt and speed; no lift if paper/ leaf is not moving

Bernoulli’s Principle Where the speed of a fluid increases the pressure in the fluid decreases. This phenomenon is due to energy conservation; when fluid’s kinetic energy increases (velocity increases) its internal potential energy (pressure) decreases. A L Still Air Wind

Home Demo: Blow It Up Hold a sheet of paper in front of your mouth and blow; the paper will rise. L A Low pressure on top; Average pressure on bottom

Blow the Roof If wind blows hard enough the low pressure above can create a large enough force to lift the roof off. New Orlean’s Superdome after hurricane Katrina L A

Class Demo: Blow the Funnel Blow hard through a funnel with a ping pong ball in the funnel’s bowl. Instead of being blown away, the ball is held tightly in the bowl. Ping Pong Ball BLOW L A L

Home Demo: Keep It Up (cont.) Bernoulli effect keeps the ball in the middle of the air stream. L A L A A A

Demo: Throwing You a Curve Putting a spin on a thrown baseball causes the airflow to be faster on one side than the other, which creates a pressure difference. No Spin Forward Motion L L L H Bernoulli Spin Depending on the axis of rotation this could be a rising fastball, a sinker, or a curve ball.

Demo: Can Crush Pour small amount of water into an empty soda can. Heat water to boiling. Quickly transfer the can, upside-down, into a pan of cold water. Soda can is quickly crushed.

Can Crush, Analyzed Steam L A A Low Pressure Atmospheric Pressure Boil the water and inside of the can fills with steam, pushing out the air. Cool the can and steam condenses back into water, leaving almost a vacuum inside. Low pressure inside and atmospheric pressure outside.

Crush the Rail Tanker Car The interior of the tank car was washed out & cleaned with steam. Then all the outlet valves were shut and the tank car was sealed. All the workers went home for the evening and when they returned, this is what they found. Apparently as the tank car cooled, it collapsed. The shell on these tank cars is 7/16 th inch thick steel.

Demo: Air Heavier than Water Fill a glass with water to the brim then place an index card on top. Hold the card while you carefully invert the glass over a sink. If the seal stays tight, atmospheric pressure will support the weight of the water.

Demo: Lift Water L A A Fill a glass underwater. Lift the glass, upside- down. Water stays in the glass because atmospheric pressure enough to balance weight of the water. Pressure of air inside the glass is below atmospheric pressure (about 1% less for a 3 inch tall glass). Weight

Demo: Drinking Straw L AA With lungs, you reduce pressure in your mouth and in the straw. The higher pressure on the outside pushes the liquid up the straw. Force due to the pressure difference must match or exceed the weight. Weight NO “SUCKING” FORCE

Next Lecture Squash & Stretch By Thursday of next week: Complete the 6 th homework (Stop-motion Animation of Falling) Please turn off and return the clickers!