IP 614 Rolling marble lab Name: Block: Date: A. Purpose In this lab you are going to see, first hand, what acceleration means. You will learn to describe such motion and its velocity. How does the position of an object change when it is accelerating? How does a position graph look like for an accelerating object? We are going to be able to answer these questions after completing this lab. B. Pre-Lab Questions a) When an object is moving down a ramp, is its speed increasing, decreasing, or staying the same? b) Sketch an object going down a ramp and on the side draw the FBD including the net force. c) Roughly sketch the position and the velocity graph of an object moving down a ramp. (Remember that if the object is moving in one direction only speed is the same as velocity) x v 0 0 t 0 0 t C. Objectives By the end of this lab students should be able to: Plot the position of the marble versus the time and be able to describe it in terms of its shape, position, velocity, and time. Plot and the velocity of the marble versus the time and be able to describe it in terms of its shape, position, velocity, and time. Calculate the average velocity for each 0.10 m segment Calculate the acceleration of the marble
D. Materials A stopwatch A 1. m track One marble One plastic bin (or any other object to increase the height of one side of the track) E. Jobs HANDLER - he or she will be in charge of the marble: RECORDER - he or she will record the measured times: TIMER - he or she will be in charge of the stopwatch: F. Procedure You will work on groups of 3 or 4 people. You will measure the time that it takes a marble to roll down a ramp. You will take measurements at 1 different positions: at 10 cm, at 0 cm, at 30 cm, at 40 cm, For each position you will repeat the experiment 6 different times. 1) Place the legs of the track (the zero side) on top of a couple of books to create an incline or ramp. It is very important that you do not change the set up during the rest of the procedure. ) The HANDLER lets go of the marble at the top of the ramp (also the zero m). At the same time TIMER starts the stopwatch. The TIMER stops the stopwatch when the marble reaches the designated mark (10 cm) 3) The RECORDER records the times in the table (next page) 4) Repeat the measurement six times 5) Repeat the measurement for the next mark: 0 cm 6) Find the average of the six trials for each of the marks At the end you should have completed the whole table, including the averages or means for each trial.
G. Data table Trial1 Trial trial 3 trial 4 trial 5 trial 6 Average Position (cm) 10 0 30 40 50 60 70 80 90 100 110 10 H. Graphs and calculations a) Graph the position of the marble versus the time (represent time in the x axis and position in the y axis). Make sure you include units. b) Looking at your graph, answer the following questions in the next page: i. Do the dots seem to be in regular time intervals? ii. Does each 10 cm interval take the same amount of time? iii. Is the motion of the marble constant or accelerated?
c) For this particular graph we are going to connect the dots, including the point (0 s,0 m). (Oh boy!) Remember that we don t usually do this, only when directly instructed. Label each line, 1 to 1, from bottom to top. Calculate the slope of each line. Each slope represents the average velocity of the marble during each interval. Use the table next page to show your work. line Rise Run? Equation Velocity calculations Plug in the numbers Solution (with units) 1 Δx 1 10 cm Δt 1 t 1 0 v 1? v 1 "x 1 "t 1 v 1 Δx 10 cm Δt t - t 1 v? v "x "t v 3 Δx 3 10 cm Δt 3 t 3 t v 3? v 3 "x 3 "t 3 v 3 4 Δx 4 10 cm Δt 4 t 4 t 3 v 4? v 4 "x 4 "t 4 v 4 5 Δx 5 10 cm Δt 5 t 5 t 4 v 5? v 5 "x 5 "t 5 v 5 6 Δx 6 10 cm Δt 6 t 6 t 5 v 6? v 6 "x 6 "t 6 v 6 7 Δx 7 10 cm Δt 7 t 7 t 6 v 7? v 7!x 7!t 7 v 7 8 Δx 8 10 cm Δt 8 t 8 t 7 v 8? v 8!x 8!t 8 v 8 9 Δx 9 10 cm Δt 9 t 9 t 8 v 9? v 9!x 9!t 9 v 9 10 Δx 10 10 cm Δt 10 t 10 t 9 v 10? v 10!x 10!t 10 v 10 11 Δx 11 10 cm Δt 11 t 11 t 10 v 11? v 11!x 11!t 11 v 11 1 Δx 1 10 cm Δt 1 t 1 t 11 v 1? v 1!x 1!t 1 v 1
d) Before we can plot the velocity we need to do some calculations: we need to find the middle of each time interval. Come again? Yes, the middle of each time interval in your graph. Let me show you: ( 0 + t 1 ) t 1 + t t + t 3 t 3 + t 4 t 4 + t 5 t 5 + t 6 t 6 + t 7 t 7 + t 8 t 8 + t 9 t 9 + t 10 t 10 + t 11 t 11 + t 1 Time (s) Velocity (m/s) e) Plot the velocity versus time (new times) in a new graph that includes the point (0 s, 0 m/s) f) Draw the best-fit line (it should include the point (0 s, 0 m/s) g) Calculate the slope of the line. This slope is a good approximation to the acceleration that the marble undergoes.
I. Analysis On a separate piece of paper and using complete sentences answer the following questions: 1) Describe the shape of the position graph. Is it a straight line? Is it a curved line? Is the position increasing, decreasing? Is the position changing in the same amount? Compare two parts at the beginning and at the end. ) Was the marble speeding up or slowing down? How do you know? 3) Was the marble accelerating? How do you know? If you don t know what acceleration means, look it up in the book. 4) Describe the shape of the velocity graph. Is it a straight line or a curved one? Is the speed increasing or decreasing over time? Does the velocity seem to be changing following a pattern? If yes, what is it? 5) Remember the marble of the inertia smorgasbord? With the strange plate (cut out plate)? Do you think that the marble rolling across the rim of the plate in a circle was accelerating? How so? Please refer to the definition of acceleration.