Motion and Design: an STC kit

Motion and Design: an STC kit Bruce Palmquist, CWU, palmquis@cwu.edu

M&D-related National Standards • Abilities necessary to do scientific inquiry • Plan and conduct investigations • Position and motion of objects • Describe changes in positions of objects using the concepts of displacement, velocity, and acceleration • Represent motion on a graph • Motion and forces • Define forces • Apply the concept of forces to motion and changes in motion • If you have a question, write it on a post-it note and stick it to the question wall.

Workshop outline • Part 1: Describing Motion • Constant motion activity • Speeding up motion activity • Graph analysis computer simulation (if time) • Part 2: Forces and Motion • Introduction to forces • “Deriving” Newton’s 2nd Law of Motion • Ramp: Forces and Motion (computer) • Part 3: Energy • Types of mechanical energy • Mini-hovercraft activity • Conservation of mechanical energy • Material at http://cwuphys106.pbworks.com/ • Click ESD 105 folder in the Navigator box on the right

Part 1: Describing Motion • Learning Objectives • Describe the motion of a fan cart using words, graphs, and “oil drop” diagrams. • Translate between a verbal description, a graph, or an “oil drop” diagram of motion. • Engage: Page Keeley Assessment Probe • Explore: Describing constant motion • Explain: Fan cart lab activity • Elaborate: Name that motion (if time) • Evaluate: Translating motion descriptions

Engage: What do you think? From Uncovering Student Ideas in Physical Science by Page Keeley and Rand Harrington, page 23-30

Engage: What do you think? • Take 1 minute to answer on your own. • Compare answers with partners for about 1 minute. Come up with a group answer to the graphing question. • Share your group’s answer with the class. From Uncovering Student Ideas in Physical Science by Page Keeley and Rand Harrington, page 23-30

Explore: Describing Constant Motion • Given whatever tools you have or can find around you, determine the velocity of your car. • Is the velocity constant? How do you know? Devise a method to test if the velocity is constant. • Summarize your method and results in a short paragraph on the provided note card. • We know the velocity is constant if equally sized displacements are travelled in equal time intervals. • The smaller the duration measured, the more accurate our proclamation that the velocity is constant.

Explore: Constant velocity Graph • The car moves equal intervals in equal amounts of time. • Car is not speeding up or slowing down (or changing direction). • Graph is a straight line. See example. • How do we know the car is not speeding up or slowing down between data points?

Explain: Fan Cart Activity • Now you will get a car that speeds up. Please be careful of the propeller. It can pinch your finger. • You will also get a tape timer, a device that puts a mark on a paper every 0.1 s or 0.025 s. • Attach about 2 meters of tape to the back of your cart. • Make a data table with about 10 position and corresponding time values. • Use Excel to make a position vs. time graph for your car. Excel worksheet template at http://goo.gl/1SvRV • When you are done with your spreadsheet and graph, give the file a creative name and email it to me at dbp1920@yahoo.com.

Explain: Graphing motion • To make a position vs time graph, plot time along the x-axis and position along the y-axis. • Determine the best fit curve using Excel (either linear or polynomial) • Email to dbp1920@yahoo.com • Excel template: • http://goo.gl/1SvRV Sample data

Explain: Increasing velocity • The car moves increasing distances in equal amounts of time. • Graph is a upward curve. • How do we know the car is not constant or slowing down between data points? • Compare different cars.

Sample Position vs. time graph • What does each parameter represent here? • Here y is position, x is time, 8.1279 is 1/2a, 22.288 is initial velocity and 0.8107 is initial position.

Explain: Acceleration • The slope of a position vs. time graph is the velocity. • If the velocity is changing, the slope at each point represents the velocity at that point. • The slope of a velocity vs. time graph is the acceleration. • Definition of acceleration: Acceleration = change in velocity/change in time a=∆v/ ∆t • The more the velocity changes for a set time interval, the greater the acceleration. • Acceleration can be positive or negative

Explain: Ticker Tape diagrams Describe the motion of the object that made each of these tapes. Justify your answer.

Explain: Ticker Tape diagrams Let’s practice this more. Constant velocity High acceleration Low acceleration

Elaborate: Describing complex 1-D motion • (If time and technology permits) • Open the Name that Motion simulation • Work in your groups. Just enter one name on the screen but fill out your own answer sheet. • View each motion. Type the number of the description on the worksheet that matches the motion.

Screen shot of Name that Motion simulation

Evaluate: Analyzing a graph • Take one minute to answer on your own. • Talk to your partners for about two minutes and compare answers. On the back of your sheet, write your group answer and explanation. • Share your group’s answer with the class. From Uncovering Student Ideas in Physical Science by Page Keeley and Rand Harrington, page 31-34

Evaluate: What understanding does each answer indicate • Bill has confused the position vs. time graph with a picture of the path of motion. He needs help understanding what a position vs. time graph tells him. • Patti seems to understand that a steeper line means faster and less steep line means slower. But she does not adequately describe the meaning of the flat line. • Kari has the best answer. She seems to understand that a flat line on a position vs. time graph means no change in position, an object that is not moving. • Mort has confused the position vs. time graph with a picture of the path of motion. He needs help understanding what a position vs. time graph tells him.

Part 2: Forces and Motion • Introduction to forces • “Deriving” Newton’s 2nd Law of Motion • Forces in 1-Dimension activity (computer)

Learning Objectives • Sketch the main forces acting on an object. • Namethe main forces acting on an object using the official naming rules. • Sketch and name the major forces acting on a rolling ball. • Use Newton's second law of motion to solve for an unknown.

Naming forces • Develop a definition of a force. • A force is a push or pull that changes the motion of an object. • Bruce’s rule for naming forces: “The (blank) push/pull of the (blank) on the (blank)” • Typical forces in k-12 science: gravitational, contact, elastic, friction, tension, electric and magnetic • A force is a vector meaning it has magnitude and direction

Forces The contact push of the table on the book. The gravitational pull of the Earth on the book.

Forces • Now I’ll give a book a push. Sketch a diagram of all of the forces acting on the book well after the push but before the book stops. • Go over Net Force Help Sheet The frictional push of the table on the book

Rolling ball motion • Sketch and name the forces for the ball • Rolling uphill • Rolling on a flat surface • Rolling downhill • In which of these situations are the forces balanced? Unbalanced?

Rolling ball motion Uphill Flat Downhill What do you notice about the uphill and downhill diagrams?

From his study of the work of Galileo and Kepler, Newton extracted three laws that relate the motion of a body to the forces acting on it. Newton’s Laws of Motion

Deriving Newton’s 2nd Law • Materials: low friction cart, kitchen scale, long hall, 1 “pusher”, 3 “riders” • The pusher will push each rider individually down the hall with the same force (same reading on the scale). • The rest of the class will note how the motion of each rider differs. • The rest of the class will also make sure the pusher keeps the same force reading on the scale the entire time.

Results of Newton’s 2nd Law demo • Another word for “rate of speeding up” is acceleration. • Conclusions? • For a constant force, as the size of the rider (m) decreased, the acceleration (a) increased. • m α 1/a (mass is inversely related to acceleration) • A more familiar way to write this is FNet = ma • Practice using newton’s 2nd Law

Newton’s 2nd law of Motion • Work on Forces in 1-Dimension at http://phet.colorado.edu/en/simulation/forces-1d or http://goo.gl/ijN0Q • What happened as the person pushed harder on the cabinet before it moved? • The friction force grew as the applied force grew. • What happened to the friction force once the cabinet started to move? • It got smaller. • What happened to the cabinet as the applied force was continually exerted on the cabinet? • It accelerated. • Review homework

1. If the total force acts in the same direction as the crate is sliding, the crate Crate was moving to the right Then, the guy pushed the crate • slows down • speeds up • remains at same speed • slows down, changes direction and then speeds up going the other way • remains at same speed, but changes direction

2. If the total force acts in the opposite direction as the cabinet is sliding, the cabinet would Cabinet was moving to the left Then, the guy pushed the cabinet • slow down • speed up • remain at same speed • slow down, change direction and then speed up going the other way • remain at same speed, but change direction

3. If there is zerototal force acting on on the refrigerator, the refrigerator would Refrigerator was moving to the right Then, the guy pushed the refrigerator • slow down • speed up • remain at same speed • slow down, change direction and then speed up going the other way • remain at same speed, but change direction

Friction • Pair up. You’ll need a pusher and a sitter. • Push the sitter’s chair lightly. What do you notice? • Push harder but not hard enough to move? What do you notice? • Once sitter starts to move, what did you notice about the “feel” of your push?

Part 3: Energy • Types of mechanical energy • Mini-hovercraft activity • Conservation of mechanical energy

Learning objectives • Use the definitions of Work, KE, PE, and TME to solve for an unknown • Given a scenario, determine whether KE, PE or TME increases, decreases or stays the same.

Work = F*d*cosq • Scenario 1: Maximum positive work done, typically means an increase in kinetic (motion) energy • Scenario 2: Maximum negative work done, typically means an decrease in kinetic (motion) energy • Scenario 3: No work done, no change in kinetic (motion) energy

Work • Which path requires the least energy to get to the top of the hill? • A  D, the straight steep path (2) • B  D, the winding path (5) • C  D, the straight non-steep path (15) • All equal (7) • Pick an answer and justify using the concept of work • Watch

Mechanical energy • There are two main types of mechanical energy • Motion energy, also called kinetic energy • KE = ½ mv2 • m=mass of the object, v = velocity • Gravitational potential energy • PE = mgh where h = height of the object above the “ground”

Work and energy • As the skier goes down the hill, how do KE, PE, work, and TME (total mechanical energy) change? Is there a relationship?

Work and energy • As the skier goes downhill, KE + PE = TME. • On the packed snow, PE = 0 and KE = TME. • TME is a constant when no work is being done by friction. • On the unpacked snow, KE goes down as friction due to snow does negative work on the skier. Let’s practice mechanical energy concepts

Energy and frictionless pucks • Use the wooden ramp, plastic puck, rubber stopper and balloon for the following. • Determine the speed of each mass puck at the bottom of the ramp without using a stop watch. Use formulas for PE and KE. Assume no frictional force. • Determine the relationship between the angle of a ramp and the speed of a frictionless puck near the bottom of the ramp. Before starting the activity, write a hypothesis and share it with the instructor. Sketch a speed vs. angle graph in your notebook. Extra challenge: derive a formula that shows the relationship. • Discuss.

Challenge solution PE at top = KE at bottom mgh = ½ mv2 gh = ½ v2 gLsinq = ½ v2 2gLsinq = v2 (2gLsinq)½ = v L h q Sinq= h/L h=L sinq

Teacher application • How can you use what you learned today to enhance your own instruction of the Motion and Design unit? • Pick a specific activity you did or concept you heard about today • Decide where it would support your teaching of the Motion and Design unit or some other topic • Briefly describe how you will use this activity or concept. • Think about this by yourself or with your school team for about five minutes. Then share with another group.

Online Resources used today • Online physics resource including tutorials, simulations, and worksheets. • I took my worksheets and notes from here. • http://www.physicsclassroom.com/ • Detailed simulations for teaching physics and other science concepts • My force “lab” activity is found here. Many other simulations for upper elementary through college students. • http://phet.colorado.edu/ • Website for my CWU Physics by Inquiry course • My CWU physics course for pre-service elementary and middle school teachers. Today’s notes found here. • http://cwuphys106.pbworks.com/

Motion and Design: an STC kit