# Peter Bohacek

Peter Bohacek is a high school physics teacher in Mendota Heights MN. With his education as an electrical engineer, Peter worked in industry for 15 years before becoming a physics teacher. An avid photographer and videographer, Peter is pursuing the opportunities of using video in physics instruction. He is compiling a library of Direct Measurement Videos that can be used to teach introductory physics mechanics.

Peter lives in Afton, MN with his wife and three children. He and his family love outdoor sports, like camping in the Boundary Waters and nordic skiing.

## Materials Contributed through SERC-hosted Projects

### Activities (22)

Conservation of Linear and Angular Momentum During a Collision part of Direct Measurement Videos:Activities

This activity is intended as an introduction to the concept of the angular momentum of a particle moving in a straight line. Students will use a video of a marble colliding with a wood block to analyze how both linear and angular momentum are conserved during a collision. Students will use a QuickTime video recorded at 960 frames per second, making measurements directly from the video using rulers and a frame-counter overlaid on the video. The video at right is a preview of the video students use for the activity.

Direct Measurement Video: Determine the Acceleration of a Toy Car part of Direct Measurement Videos:Activities

This is a short activity intended to allow students to practice kinematics using a video of a familiar object: a spring-powered toy car. Students measure displacement and elapsed time from the video and use these measurements to calculate average speed. Observing that the car has an initial speed of zero, students can find the final speed and acceleration. Students will use a QuickTime video recorded at 240 frames per second, making measurements directly from the video using a ruler and a frame-counter overlaid on the video. The video at right is a preview of the video students use for the activity.

Direct Measurement Video of a Ball Sliding and Rolling part of Direct Measurement Videos:Activities

This activity is intended to help students understand and apply rotational mechanics. Students will use a video of a billiard ball that is sliding and rolling along a metal track. Students can use the video to determine what coefficient of friction would cause the motion of the ball. Students will use a video recorded at 480 frames per second, making measurements directly from the video using a frame-counter and numerical data overlaid on the video. The video at right is a preview of the video students use for the activity.

Direct Measurement of a Hockey Slap Shot part of Direct Measurement Videos:Activities

This activity is intended to help students understand and apply concepts in physics mechanics to a real-world situation. Students will use a high speed video of a hockey slap shot, making measurements directly from the video. Students can use the video to determine the average force the hockey stick exerts on the puck while the stick and puck are in contact. This is an example of an open-ended problem in that students are given little numerical information and several different strategies and concepts can be used. Students should be familiar with the concept of velocity, acceleration, Newton's laws of motion, and the concepts of momentum and impulse. Unlike traditional a word-problem where students are given the numerical information they need to solve the problem, students must make measurements from the video to determine their answer. Ideally, students are not given hints or even told which concepts to use, as these steps are essential parts of their analysis. Students will use a high speed video recorded at 240 frames per second, making measurements directly from the video using a frame-counter, a ruler and numerical data overlaid on the video. The video at right is a preview of the video students use for the activity.

Introduction to Direct Measurement Video: Measure the Velocity of a Roller Coaster part of Direct Measurement Videos:Activities

This activity can be students' first exposure to using Direct Measurement Videos in physics. Students will use a video to make measurements that will allow them to calculate the speed of a roller coaster. This activity will also help students understand the concept of average velocity.

Direct Measurement Video of a Bouncing Ball part of Direct Measurement Videos:Activities

This is an activity presents an opportunity for students to practice problem solving using a direct measurement video. The video shows an inflatable rubber ball bouncing across a stage. Students make measurements from the video and calculate the velocity for the ball just as it completes the first bounce and leaves the floor on the way up. Students will use a high speed video recorded at 120 frames per second, making measurements directly from the video using one given dimension and a frame-counter overlaid on the video. The video at right is a preview of the video students use for the activity.

Direct Measurement Video of a Bouncing Ball part of Pedagogy in Action:Library:Using Direct Measurement Videos to Teach Physics:Examples

This is an activity presents an opportunity for students to practice problem solving using a direct measurement video. The video shows an inflatable rubber ball bouncing across a stage. Students make measurements from the video and calculate the velocity for the ball just as it completes the first bounce and leaves the floor on the way up. Students will use a QuickTime video recorded at 120 frames per second, making measurements directly from the video using one given dimension and a frame-counter overlaid on the video. The video at right is a preview of the video students use for the activity.

Direct Measurement Video of a Ball Sliding and Rolling part of Pedagogy in Action:Library:Using Direct Measurement Videos to Teach Physics:Examples

This activity is intended to help students understand and apply rotational mechanics. Students will use a video of a billiard ball that is sliding and rolling along a metal track. Students can use the video to determine what coefficient of friction would cause the motion of the ball. Students will use a QuickTime video recorded at 480 frames per second, making measurements directly from the video using a frame-counter and numerical data overlaid on the video. The video at right is a preview of the video students use for the activity.

Direct Measurement Video of a Toy Car Accelerating part of Pedagogy in Action:Library:Using Direct Measurement Videos to Teach Physics:Examples

This is a short activity intended to allow students to practice kinematics using a video of a familiar object: a spring-powered toy car. Students measure displacement and elapsed time from the video and use these measurements to calculate average speed. Observing that the car has an initial speed of zero, students can find the final speed and acceleration. Students will use a QuickTime video recorded at 240 frames per second, making measurements directly from the video using a ruler and a frame-counter overlaid on the video. The video at right is a preview of the video students use for the activity.

Conservation of Linear and Angular Momentum During a Collision part of Pedagogy in Action:Library:Using Direct Measurement Videos to Teach Physics:Examples

This activity is intended as an introduction to the concept of the angular momentum of a particle moving in a straight line. Students will use a video of a marble colliding with a wood block to analyze how both linear and angular momentum are conserved during a collision. Students will use a QuickTime video recorded at 960 frames per second, making measurements directly from the video using rulers and a frame-counter overlaid on the video. The video at right is a preview of the video students use for the activity.

Introduction to Direct Measurement Video: Measure the Velocity of a Roller Coaster part of Pedagogy in Action:Library:Using Direct Measurement Videos to Teach Physics:Examples

This activity can be students' first exposure to using Direct Measurement Videos in physics. Students will use a video to make measurements that will allow them to calculate the speed of a roller coaster. This activity will also help students understand the concept of average velocity.

Conservation of energy of while rolling down a hill part of comPADRE Pedagogic Library:Teaching with Data:Examples

When studying conservation of energy, we often use the example of an object sliding or rolling down a ramp. Here is a real-life example that we can use to see whether mechanical energy really is conserved when objects roll down hills. Students analyze video clips of children rolling down a driveway on roller blades and various bikes. Using the techniques described in the activity called Measuring velocity of objects using video clips, students can determine the velocity of the kids rolling at the bottom of the hill. The video clips also include the height of the hill. Students can use this information to determine the loss of mechanical energy, and look for a relationship between the type of vehicle used to roll down the hill and the amount of mechanical energy lost to friction.

Conservation of energy of a rollercoaster using high speed video part of comPADRE Pedagogic Library:Teaching with Data:Examples

loading the player jwplayer('flashv509693').setup({ flashplayer: '/scripts/jwplayer/v5.player.swf', bufferlength: 5, controlbar: 'bottom', skin: '/scripts/jwplayer/v5.modieus.zip', // Inline function below prepends 'http:' or 'https:' to url if it starts with // file: (function(url){return url.match(/^\/\//) ? window.location.protocol + url : url})('//d32ogoqmya1dw8.cloudfront.net/files/introgeo/teachingwdata/examples/rollercoaster_video.v4.m4v'), height: 283, width: 450, image: '//d32ogoqmya1dw8.cloudfront.net/images/thumbs/files/24619_640.jpg', plugins: { gapro: { accountid: 'UA-355624-1'} } }); High speed video of a roller coaster allows students to perform careful analysis of a familiar situation. Students use high speed video to determine whether a roller coaster is an example of a system in which mechanical energy is conserved. Students use frame counting to measure the speed of a roller coaster as it heads up a hill, and then measure the speed as the roller coaster comes back down the hill. The outcome of the measurements depends on which part of the roller coaster they measure because a motor continues to propel the roller coaster until it begins to climb the hill. This activity follows on the activity Measuring velocity of objects using video clips.

Measuring velocity of objects using video clips part of comPADRE Pedagogic Library:Teaching with Data:Examples

loading the player jwplayer('flashv428537').setup({ flashplayer: '/scripts/jwplayer/v5.player.swf', bufferlength: 5, controlbar: 'bottom', skin: '/scripts/jwplayer/v5.modieus.zip', // Inline function below prepends 'http:' or 'https:' to url if it starts with // file: (function(url){return url.match(/^\/\//) ? window.location.protocol + url : url})('//d32ogoqmya1dw8.cloudfront.net/files/introgeo/teachingwdata/examples/tennis_ball_drop_flash.v4.m4v'), height: 330, width: 400, image: '//d32ogoqmya1dw8.cloudfront.net/images/thumbs/files/24529_720.jpg', plugins: { gapro: { accountid: 'UA-355624-1'} } });Usually we ask students to solve word problems where they are given all the information they need to solve the problem: "A car moves with velocity of 20 m/s..." In this activity, students learn to extract data about the motion of objects using videos. Several examples of videos are provided, as well as instructions for using some of these videos to measure velocity. Once this technique is mastered, students can begin to use the velocities of objects in the videos to explore other aspects of mechanics, such as collisions, conservation of energy, or projectile motion. If the video is taken carefully, students do not need video analysis software, just a simple video playback software, such as Quicktime player, that allows students to advance the video one frame at a time.

A simple motor/generator demonstration for use in interactive lecture part of comPADRE Pedagogic Library:Teaching with Interactive Demonstrations:Examples

This image shows a simple motor/generator apparatus that can be used to demonstrate Faraday's Law of Induction and the Lorentz force. This apparatus is easy and inexpensive to construct and provides a clear and compelling demonstration of Faraday's Law of Induction and the Lorentz force. Two magnets are suspended from springs so that they are free to oscillate vertically. These magnets are placed inside two solenoids (coils of wire). The solenoids are connected. Moving one of the magnets induces a current in the solenoid. This current flows to the other solenoid where is generates a force on the other magnet, causing it to move. Connecting the solenoid leads in different ways produces different results. The instructor can ask students to predict the results of each connection.

Analysis of simple harmonic oscillator in a single video clip part of comPADRE Pedagogic Library:Teaching with Data:Examples

A video clip of a glider on a low-friction air track can be used to analyze many aspects of simple harmonic motion. This clip includes graphs that are synchronized to the motion that show position vs time, velocity vs time, and acceleration vs time. Using this graph, students can study many qualitative and quantitative aspects of simple harmonic motion. Included below are the video clip, and instructions for use, included sample questions.

Contructing a projectile launcher and free falling target part of comPADRE Pedagogic Library:Teaching with Interactive Demonstrations:Examples

This demonstration is an implementation of a classic physics demonstration usually called "the monkey and the hunter." The information posted here is a description of how we constructed a projectile launcher and a target that begins to fall at the same time the projectile is launched. The completed project is a spectacular demonstration of the concepts of projectile motion. This demonstration can be used as part of an interactive lecture.

An electrostatics puzzler part of comPADRE Pedagogic Library:Teaching with Interactive Demonstrations:Examples

A simple demonstration will tests students' understanding of electrostatics. This puzzler stumps even experienced physics educators and is sure to entertain a physics class. A plastic rod is charged using a piece of animal fur. The rod is touched to an aluminum pop can, creating a faint popping sound indicating that charge is transferred to the can. Next, the rod is held next to the can. Will the can be attracted to the rod, repelled by the rod, or neither of these? Before they see the outcome, students must make a prediction and work to convince other students that their prediction is correct. Only after all arguments are exhausted is the answer revealed. A video provided here describes the demonstration.

Lab: Horizontally Launched Projectiles (with uncertainty analysis) part of comPADRE Pedagogic Library:Measurement and Uncertainty:Examples

This is a version of the time-tested lab where students roll a ball off a table top and use kinematics in two dimensions to try to predict where the ball will land. While many versions of this lab have been previously published, in this version students determine the uncertainty of all measurements and uncertainty of their prediction. The techniques and vocabulary are consistent with the Introduction to Measurement packet. In most versions of this lab, students predict the distance away from the table where they think the ball will land. Then, students launch the projectile to see whether their prediction is right. In this version, students use the concept of uncertainty and predict a range of distances between which they predict the ball will land. Then they launch the projectile to see whether their prediction is correct within their stated range of certainty.

Introduction to Measurement (advanced high school/intro college level) part of comPADRE Pedagogic Library:Measurement and Uncertainty:Examples

30-page illustrated guide to fundamentals of measurement. This is intended to be a clear, comprehensive overview of effective measurement technique. Intended for advanced high school or introductory college level students. Includes worked examples and problems.

Lab: Measuring the Speed of Sound in Air (with uncertainty analysis) part of comPADRE Pedagogic Library:Measurement and Uncertainty:Examples

Students use a microphone and Vernier LabQuest to record the sound of a finger-snap echo in a 1-2 meter cardboard tube. Students measure the time for the echo to return to the microphone, and measure the length of the tube. Using their measurements, students determine the speed of sound. While other authors have produced similar labs, this version includes uncertainty analysis consistent with effective measurement technique as presented in the module Measurement and Uncertainty.

Activity: Measure Your Reaction Time part of comPADRE Pedagogic Library:Measurement and Uncertainty:Examples

This is a lab activity that allows students to collect data to practice using effective measurement. While other authors have produced similar labs, this version includes uncertainty analysis consistent with effective measurement technique as presented in the module Measurement and Uncertainty.

### Teaching Method Modules (2)

Direct Measurement Videos part of Direct Measurement Videos

Direct Measurement Videos are short, high-quality videos of real events that allow students to easily explore, measure, and predict physical phenomena. Several of the videos are paired with classroom-ready activities that integrate videos into the introductory mechanics curriculum.

Integrating Measurement and Uncertainty into Science Instruction part of comPADRE Pedagogic Library:Measurement and Uncertainty

"When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre ...

### Other Contributions (4)

Direct Measurement Video of Einstein riding the Graviton part of Direct Measurement Videos:Activities

This Direct-Measurement Video gives students an opportunity to apply Newtonian mechanics to a model of an amusement park ride. An Einstein "action figure" (doll) is pinned against a vertical wall on a rotating platform. As the platform slows its rotation, Einstein slips down the vertical surface. Students can make measurements and calculations to determine the minimum speed that will keep Einstein from sliding, and calculate the coefficient of static friction between Einstein and the wall. In addition, students can develop an experiment that will let them determine the coefficient of sliding friction as Einstein slides down the vertical surface.

Measuring the coefficient of friction of a skater on ice part of comPADRE Pedagogic Library:Teaching with Data:Examples

Students use a video clip of a gliding ice skater to determine the coefficient of friction of the skater on ice. Vernier LoggerPro's video analysis tools are used to plot the velocity vs time. From the slope of this line, students can determine the acceleration and use Newton's Second Law to calculate the coefficient of sliding friction between the skates and the ice.

Determining Measured Values and Uncertainty part of comPADRE Pedagogic Library:Measurement and Uncertainty:Examples

In this activity, students practice reading various measurement devices, such as graduated cylinders, electronic balances, voltmeters and spring scales. In each case students determine the range of possible values for the measurement. They express this range as a measured value with uncertainty in three forms, including a number line with error bars.

Performing Calculations using Measured Values that Include Uncertainty part of comPADRE Pedagogic Library:Measurement and Uncertainty:Examples

In this activity, students practice performing calculations using measured values that include uncertainty. Students measure the mass (using an electronic balance) and volume (by water displacement) of pennies and use the values to calculate the density of the pennies. All measured values include uncertainty, and students practice using the rules for making calculations using numbers that include uncertainty. As the students increase the number of pennies they use, the relative uncertainty of their calculated density decreases. Students will see factors that affect the uncertainty of each measurement and also how the uncertainty of each measurement contributes to the uncertainty of their calculated results. Provided here is a data set for copper pennies (pre-1982) and zinc/copper pennies (post 1982). Students can use the data to identify what these pennies are made of, but only when the uncertainty of their calculated density is lower than the difference between the density of copper and the density of zinc.