# Based on the function and location of the Vernier Motion Sensor, what object is described by the graphs: or ?

MOUNT ROYAL UNIVERSITY
Department of Chemistry and Physics
PHYS 1201
Lab 7: Newton’s Second Law Part 1

Name:

Preparation: Read Classical Physics: Sections 4.5, 4.6, and 5.2.

Learning goals: Use Newton`s second law to explore the relationship between net force, mass, and acceleration.

Equipment: Atwood Machine simulation from The Physics Aviary

Experiment

For this activity, we will use a simulation to explore acceleration of objects in an Atwood Machine.

1. Open the simulation located at http://www.thephysicsaviary.com/Physics/Programs/Labs/AtwoodLab/
2. Take a few minutes to familiarize yourself with the settings.  Once you have, press “Start” and observe the behaviour of the simulation.

3. Notice that two graphs are populated as the simulation runs: a Position vs Time graph and a Velocity vs Time graph.   These graphs represent data collected by the Vernier Motion Sensor, depicted by a black rectangle in the simulation and circled in red in Figure 1.  This sensor uses ultrasound to determine the distance to the nearest object by timing how long it takes for a signal that it emits to be reflected.

Figure 1. Modified Atwood machine

1: answer the following questions:

1. Based on the function and location of the Vernier Motion Sensor, what object is described by the graphs:  or ?

2. Based on the direction that the object travelled and the sign convention of the Position vs Time graph, what is the sign convention of the vertical directions in this simulation?  Draw the coordinate system below:

3. What does the shape of the Velocity vs Time graph tell you about the motion of the object?

4. How can you use the Velocity vs Time graph to determine the acceleration of the object?

The acceleration of is given by the following equation that you have derived in your pre-lab:

,                                        (Equation 1)

where        and

question 2:

1. Do you expect the magnitude of acceleration for each mass to be less than g, equal to g, or greater than g? Explain your reasoning using Equation 1.

1. For this experiment, you will manipulate the variable , while holding the variable  constant for every trial. Use the arrows that control each mass in the simulation to explore the possible mass settings.  You will need to conduct 7 different experimental trials, each with different  mass values.  For all 7 trials, the total mass ( ) must remain constant while the difference between  and  is altered for each trial.  Choose a value for  that allows you to achieve this:

______________

• Fill in the values for  and  that allow you to achieve these trials in the corresponding columns of Table 1.

Click on the “Earth” label repeatedly until the environment is set to Mars.

For each trial, set masses according to values in Table 1 and press “Start”.  Use the Velocity vs Time graph to calculate the acceleration of the mass.  Indicate the two points that you used from the graph to calculate the acceleration.  Be sure not to use data points, but to infer a best fit line (you can hold a ruler up to your screen).

d. Take a screenshot of the apparatus for Trial 1 showing the settings and resulting Velocity vs Time graph.  Place this in the Appendix at the end of the document.

Table 1. Data for the Atwood Machine

• Show a sample calculation of how you determined the acceleration for Trial 1:

question 3.

a. Create a graph by hand of acceleration vs  on mm spaced graph paper.  Be sure to label your axis, provide a title.  Error bars are not required for this lab.

• Draw a best fit line of the data.  Calculate the slope of the line (including units).  Show your work here:

Group Checkpoint You must complete up to this point at a minimum before meeting with your group members and instructor during the synchronous lab hour.

Include a copy of the graph in the Appendix.

• Using this axis arrangement, determine the meaning of the slope of this graph.  To do this, insert Equation 1 into the blanks below and compare it with the equation for a line, drawing circles to relate y, m, x, and b to terms in Equation 1 as was demonstrated in the Lab Standards Manual:

Write the theoretical expression that is represented by the slope:

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question 4.

1. As you have already calculated the numerical value of the slope, how can you use the slope to determine the experimental value of g?  Write down the algebraic expression for g that you will use.

2. Use the value of the slope to find the experimental value of g.  Show all your work, including units.

3. What is the theoretical value of g that you expected to obtain?  Is this value similar to your experimental value? (Because you did not calculate any experimental uncertainties today, you cannot use a range to state whether they are consistent with each other).
• Write a conclusion based on the lab you did(include errors, symmetrical or etc….)

Appendix

Include the following in this section:

1. Screenshot of the apparatus collecting your first datapoint
2. The acceleration vs  graph with best fit line, indicating the points used for slope calculations.
3. Any other drawings that you weren’t able to include in line with the document, labelling them clearly and indicating their location in the Appendix in the original question.