Upcoming Deadlines Sixth Homework (Stop-motion Animation) Due Tuesday, Sept. 25 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 Tuesday, Oct. 2 nd (In two weeks) 10 points (if late, 5 points) For full schedule, visit course website: Have clicker ready

Extra Credit Opportunity Visit the Cartoon Art Museum in SF to see the Avengers Assemble! exhibition. Exhibit runs until Oct. 7 th Turn in proof of attendance (ticket receipt) for 10 points extra credit. For info: cartoonart.org

Extra Credit Opportunity Attend a screening at Palo Alto International Film Festival (Sept ) Turn in proof of attendance (ticket receipt) for 10 points extra credit. For info:

Extra Credit Opportunity Attend a screening or event at the Mill Valley Film Festival (Oct. 4 th th ) Turn in proof of attendance (ticket receipt) for 10 points extra credit. For info:

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.

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 Tuesday, September 25 th 20 points (if late, 10 points) The top three animation clips in the class will receive a bonus of 20 extra points.

Survey Question Do you have some experience with creating stop-motion animation. A)Yes B)No

The League of Extraordinary Gentlemen (2003) In this scene, Sean Connery jumps out the side of a speeding car and lands on his feet.

A)Keep moving in the same direction as the moving car. B)Go in the opposite direction from that of the moving car. C)Land just as he does in the movie; this was actually done by a stuntman. Review Question In this scene, Sean Connery jumps out the side of a speeding car and lands on his feet. In reality, he would:

A) Keep moving in the same direction as the moving car You are moving at the same speed as the car when you jump out so you keep moving forward. Jumping out of a Car Your path You’ll start losing speed after you hit the ground so, relative to the car, you’ll fall behind as the car continues speeding along. car

Review Question The accident-prone Wile E Coyote walks off a cliff carrying an anvil. If he lets go of the anvil, he’ll fall: A)Slower B)Faster C)At the same speed

Wile E Coyote with Anvil The answer is: A)Slower You reach terminal speed when the force of air resistance balances your weight. The less you weight, the less air resistance is needed so the terminal speed is also lower (lower speed lower air resistance).

Review Question Water Air A water-filled balloon falls much faster than a balloon filled with air. If the balloons are the same size, the force of air resistance (measured in ounces) is larger for the: A)Air-filled balloon B)Water-filled balloon C)Same for both balloons

Balloon Drop Because the water balloon falls faster, the air resistance force on a water balloon is larger than on an air-filled balloon of the same size. However, a few ounces of air resistance force is insignificant for a water balloon weighing several pounds. Water Air Gravity Air Resistance B) Water-filled Balloon

Creating Action Part II

Newton’s Laws of Forces Newton established three basic laws to explain how motion is caused by forces: Law of Inertia Law of Acceleration Action-Reaction Principle The Law of Inertia explains motion without forces (or with only balanced forces). The Law of Acceleration explains motion with unbalanced forces. Sir Isaac Newton

Demo: Spool Pull on string wrapped around a spool. Force is to the right-to-left. In what direction does the spool move? Spool moves? Pull Spool moves?

Force and Direction Objects always change their velocity in the direction of the applied force. Pull Motion

Demo: Tricycle Pull on tricycle pedal with a string. Which direction does the tricycle move? Bike moves? Pull Pedal in top position Pedal in bottom position

Demo: Tricycle Notice that the position of the lower pedal moves forward as the wheel is turning. CLICK

Forces & Slowing In/Out When a force pulls in the direction that an object is already moving, the object slows out (accelerates) If a force pushes opposite to the direction of motion then the object slows in (decelerates) Force Moving this way Force Moving this way

Forces & Path of Action When a force is perpendicular to the path of action then it deflects the motion into an arc. Force (up & left) Moving this way If force is at an arbitrary angle then both timing and path of action are affected.

More Force, More Acceleration The greater the net force on an object, the greater the acceleration of that object.

Simple Addition of Forces When two forces pull in parallel directions it’s simple to add them to get the total force. Gravity (Weight) Air Resistance Total Force For example, if a bubble weighs 3 oz and air resistance is a force of 2 oz then the total force is 1 ounce.

Air Resistance on a Falling Object Gravity force on an object (i.e., weight) is constant but air resistance depends on an object’s speed. As a falling object gains speed, the resistance force gets larger so the net force decreases. Net force is sum of: Weight (downward) Resistance (upward) Net Force 100 lbs. Net Force 20 lbs. Net Force Zero

More Mass, Less Acceleration The greater the mass of an object, the less it accelerates when acted on by a force.

Motion Graphs - Speed Fast Slow Frame Distance Greater the speed, steeper the slope.

Motion Graphs - Acceleration Big Acceleration Small Acceleration Frame Distance Greater the acceleration, greater the curvature.

Speed & Acceleration The change in the spacings gives the acceleration. The spacing between positions gives the speed.

Odd Rule & Forces The Odd Rule applies if forces are constant. Forces here are constant; the support force by the ground balances the weight, leaving only the friction force. Support Friction Gravity (Weight) Apex 1 3 5

Complex Path of Action When forces are not constant then the timing, spacing, and path of action are complex.

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

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

Buoyancy A Buoyant force pushing submerged objects upward is also due to a pressure difference. H HIGH PRESSURE ATMOSPHERIC PRESSURE H HIGHER PRESSURE H The pressure increases with depth due to the weight of the liquid.

Demo: Magdeburg Hemispheres Pair of hemispheres fit together with air- tight seal Most of the air is pumped out from the interior. Air pressure holds the two pieces tightly together. A A A A L A L - Atmospheric pressure - Low pressure

Demo: Vacuum Cannon

Demo: Peeps in a Vacuum Before vacuum pump is turned on (normal atmospheric pressure) After vacuum pump is turned on (very low air pressure in chamber) After vacuum pump is removed (back to normal atmospheric pressure)

Total Recall (1990)

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

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

The Curse of the Were-Rabbit (2005)

Quiz Question: Rabbit Vacuum Is it actually possible to use a vacuum to pull rabbits out of their holes? A)Yes B)No

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

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

Fluid Flow and Pressure Pressure varies when air is moving and we see this effect in the flapping of a flag and the ocean waves kicked up by a strong wind.

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

Paper Drop Test

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

Waves and Bernoulli’s Principle Wind blowing over the ocean causes waves to build due to Bernoulli’s principle. Where is the pressure lowered? L A L A A Air moves fastest at the tops of the waves so pressure is lowest there. The lower portion of the wave is blocked from the wind so air above the water is at atmospheric pressure.

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

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

Aerodynamics for Race Cars Airfoil on a race car is an upside-down wing that increases traction (friction) by increasing downward pressure.

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.

Curveball Flow Pattern L H

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

Next Lecture Squash & Stretch By Tuesday of next week: Complete the 6 th homework (Stop-motion Animation of Falling) Remember to turn off your clickers!