Laboratory Activity 1: Position Graphs s2

Group member names: -Rebecca Wade Laboratory Activity 2: Velocity - Graphs -

Objectives  Explore how motions are related to velocity-time graphs  Relate velocity-time graphs and position-time graphs

Equipment  Computer  Ultrasonic motion sensor  USB Link

Activity One: Simple graphs Prediction 1: Using the line tool on the drawing toolbar of Word, draw a line on both the position and velocity graph below predicting the shape of a curve for a person walking away at a slow, steady pace. y n t i o i c t i o l s e o V P

Time Time

Set up the equipment: Obtain a USB Link and a motion detector as in the previous lab. Open the experiment file called VelocityGraphs.ds to display velocity vs. time axes. You can find it by going to the networked disk “PLAB” (usually disk G:), in that opening the folder “Plab”, then finding the folder for Physics 201, and then looking in the folder for Lab2. Experiment: Set the detector up as in the previous lab and walk away backwards at a slow, steady pace, while watching the graph on the screen. When you have a nice graph, copy the graph and paste it in the section below. Question 1: How did the result compare to your prediction? If it was different, do you now understand why it is the way it is? Note: you should not go back and change predictions. There is absolutely nothing wrong with making a prediction and then finding out it wasn’t quite correct. In fact, that can show that you are learning. They are very similar but the slope of the position graph and my prediction are also at odds because it is hard to predict ones pace.

Prediction 2a: How will the graph be look if you walk away from the detector at a faster pace? y n t i o i c t i o l s e o V P

Time Time

Prediction 2b: How will the graph be look if you walk towards the detector at a slow, steady pace? y n t i o i c t i o l s e o V P

Time Time

Prediction 2b: How will the graph be look if you walk towards the detector at a fast, steady pace? y n t i o i c t i o l s e o V P

Time Time

Experiment: Without erasing your last data run, start about ½ meter from the detector and walk away at twice the rate. Then take another run, starting away from the detector and walking toward it slowly. Finally, walk toward the detector quickly. Label each run as to which it is by clicking twice (not too fast) on the labels “Run 1” etc. in the menu list on the upper left-hand window and giving them more descriptive names. Then copy and paste your graph in the space below the same way as above. Question 2: What does distance away from the horizontal (time axis) tell you about the motion? What does the sign (above or below the axis) tell you about the motion? What would a graph look like for someone standing still? The sign tells you that you are moving away from the origin when the velocity graph’s curve is above the axis and toward when below. It would at zero velocity or on the x-axis.

Activity Two: More complicated motion Prediction 3: Sketch on the graph below a prediction for the following motion: walking away from the detector quickly, stopping for a while, and then walking toward the detector slowly. y n t i o i c t i o l s e o V P

Time Time

Question 3: Try walking the way described. How does it compare to your predictions? It does not have the quick stops and starts as mine did and it could actually stayed connected on the velocity graph.

Open the experiment file called VelocityMatch.ds. A velocity graph like that shown below will appear on the screen.

(from RealTime Physics (Electronic Version) by Prisilla Laws, et al., John Wiley and Sons, NY, 1999)

Prediction 4a: Describe in words how you would move in front of the motion detector in order to create the graph. Discuss your answer with your group until you all agree. No movement for four seconds walking away from detector at constant velocity for .5 m/s for next four seconds again you wait four seconds then six seconds at constant velocity at .5 m/s toward detector last two seconds no movement.

Experiment: Walk in front of the motion detector and try to create the graph. You may try a number of times. It helps to work in a team. Get the times right. Get the speeds right. Question 4a: How did your prediction match how you had to move? How did you have to move when the line was above the axis? Below the axis? On the axis? It matched pretty well. For above the line I had to move away from the origin while for below I moved towards and to be on the line I stood still. Question 4b: Did you run out of room for the motion? Can you tell from a velocity graph where you need to start? Why or why not? I almost ran out of room since you cannot tell where to start from the velocity graph. The velocity graph can only tell you the velocity, time, acceleration (slope) and total displacement (area under the curve). It tells you how much distance changed not where it began or ended.

Summary The following questions will help you get the main ideas out of this lab. You should find these straightforward questions, but take the time to talk it over with your team and write complete answers to these questions. You may find your answers here to be the most useful part of this lab down the road. Summary 1: In a velocity graph, what does the horizontal distance from the axis of the graph mean? What does the vertical distance from the axis mean? What does it mean if the line is above the axis, on the axis, or below the axis? The horizontal distance is time how long you traveled at that speed. The vertical distance is the velocity of the object moving. On the axis is standing still while above it means you are moving away from the origin and below the axis means you are moving toward the origin. Summary 2: How are position and velocity graphs related? What aspect of a position graph and what aspect of a velocity graph tells us how fast something is moving? What aspects of each graph tell us what direction something is moving? The slope of the position graph is the horizontal line in the velocity graph. The slope in the position graph is the velocity while the point on the velocity graph is the velocity. Positive slope or line above the axis tells us that the object is moving away from the detector while negative slope or a line below the axis tells us that the object is moving towards the detector.

Summary 3: How do you know your above statements are true? What experimental observations and/or logical reasoning can you give to justify what you said in summary questions 1&2? Personally observing these happenings as well as realizing that velocity is m/s and the slope of the position graph is m/s. A negative slope on the position graph would then come out, as below the x-axis and the positive slope above the x-axis and that a slope of zero would then be on the x-axis.