Upcoming Deadlines Fifth Homework (Video analysis of jump) Due Thursday, Sept. 29 th (This week) 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. 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.

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, Oct. 6 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 You have some experience with creating stop-motion animation. True or False?

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)Roll forward from where he lands, in the direction of the moving car. B)Roll backwards from where he lands. C)Land just as he does in the movie; this was actually done by a stuntman. The League of Extraordinary Gentlemen (2003) In this scene, Sean Connery jumps out the side of a speeding car and lands on his feet. In reality, he would:

A) Roll forward You are moving at the same speed as the car when you jump out so you will roll 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

Creating Action Part II

Estimating Terminal Speed Air Resistance Gravity Terminal speed of a rectangular object (with the density of water) falling flat is approximately: (Speed) = (50 m.p.h.) x  T where T is thickness in inches. Thickness, T TT Terminal Speed 1 / 100 inch 1 / 10 5 m.p.h. ¼ inch½25 m.p.h. 1 inch150 m.p.h 4 inch2100 m.p.h. 9 inch3150 m.p.h T

Terminal Speed & Density The denser the material, the higher the terminal speed. The table gives the terminal speed for density of water. The terminal speed for wood is about the same as for water since the density of wood is close to that of water. The terminal speed for rocks is about 50%-75% larger since rocks are 2-3 times denser than water. Metals, like iron and copper, are 8-9 times denser than water so the terminal speed is about three times larger. For example, a brick’s terminal speed is about 100 m.p.h. (Falling flat so thickness is 2 inches)

Drop the Ball A golf ball and a ping pong ball are about the same size; golf ball is heavier. Drop both from the roof of a 10 story building. What happens? A)Balls hit the ground at the same time and hit the ground with the same speed. B)Balls hit the ground at the same time but the golf ball has a higher speed. C)The golf ball hits the ground first but they both hit the ground with the same speed. D)Golf ball hits the ground first and it also has a higher speed.

Drop the Ball Golf Ball Ping pong Ball D) Golf ball hits the ground first and it also has a higher speed. Ping pong ball is less dense so its terminal speed is slower than the golf ball. The golf ball falls faster, which also means it reaches the ground first.

Leaf/Paper Terminal Speed The terminal speed of a leaf or sheet of paper is about 5 feet per second, which is about 3½ miles per hour (or 2-3 inches per frame). Terminal speed is reached after falling about 4 frames (flat orientation). Air Resistance Gravity Density of paper about the same as wood.

Falling Coffee Filter Tracked falling of a coffee filter. Distance Fallen Time Accelerates in first 1 / 3 second Constant Speed Click

Air Resistance Threshold Distance fallen from apex Speed (miles per hour) 1 foot5 4 feet10 9 feet15 16 feet20 25 feet25 49 feet feet feet feet150 Air resistance is only noticeable once an object’s speed gets close to its terminal speed. This table gives the speed of an object from the distance it’s fallen it there is no air resistance. For example, since a brick’s terminal velocity is 100 m.p.h. then air resistance is not noticeable for a 100 foot drop.

Cat Drop Video Reference

Cat Drop Motion Graph Good parabolic arc; no noticeable air resistance

Home Demo: Keep It Up You can estimate the terminal speed as the wind speed needed to support the object.

Indoor Skydiving iflysfbay.com With a big fan (blowing mph), you can experience terminal speed and skydive indoors.

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 from 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

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.

Demo: Bowling Ball in a Bag Can slowly lift a plastic bag holding a bowling ball by exerting only a little more force than the weight of the ball. If we try to lift the bag quickly, this large acceleration requires a very large force. If we pull up too quickly then this large force will break the bag.

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.

Differential Calculus You now know basic differential calculus. The difference between the spacings is the increment, which gives the acceleration. The difference between the positions of the ball is the spacing, which gives the speed.

Law of Acceleration If the total force equals the object’s weight then the spacing is the same as when falling. If the total force is greater than the weight then the spacings and increments are larger. If the total force is less than the weight then the spacings and increments are shorter. The bigger the friction force, the quicker the timing (shorter the spacings).

Atmospheric Pressure The weight of the air above us creates atmospheric pressure, a force of about 15 pounds per square inch. We live at the bottom of an ocean of fluid—the fluid is air & “ocean” is the atmosphere.

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: 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)

Next Lecture More about forces By Thursday of this week: Complete 5th homework (Video analysis of jump) By Thursday of next week: Complete the 6 th homework (Stop-motion Animation of Falling) Please turn off and return the clickers!