Description

Physics 250: Understanding Motion – Distance, Time and velocity

Purpose:

The purpose of this activity is to introduce the relationships between the motion of an object and graphs of

position vs. time and velocity vs. time for the moving object.

Theory:

When describing the motion of an object, knowing where it is relative to a reference point, how fast and in

what direction it is moving, and how it is accelerating (changing its motion) is essential. In the following

simulation, the change in position from moment to moment is expressed as a velocity magnitude (in meters

per second). The change in velocity from moment to moment is expressed as an acceleration magnitude (in

meters per second per second). The position of an object at a particular time can be plotted on a graph as a

function of time. You can also graph the velocity and acceleration of the object versus time. A graph is a

mathematical picture of the motion of an object. For this reason, it is important to understand how to

interpret a graph of position, velocity, or acceleration vs. time. In this activity, you will plot graphs in realtime, that is, as the motion is happening.

A. Constant velocity (zero acceleration)

Procedure: For this activity, please go to the following link: and

adjust the initial conditions for position, velocity and acceleration of both blue and red cars as

shown in figure 1. Throughout the entire experiment we keep the initial conditions for the blue car

the same and we change the conditions for the red car to study its motion and corresponding graphs.

After adjusting the variables, click on “Reset” and start clicking on the forward step

button.

Once you have reached t = 1.0 s, record the values of red car’s position in an excel spreadsheet,

following the formatting given in table 1. Repeat every second (Δt = 1s), until you reach t = 10.0 s.

You may need to use the “Zoom In” and/or “Zoom Out” features to get a good reading.

You can calculate the average velocity as we learned in the lecture by using the definition of

average velocity 𝑣𝑣𝑎𝑎𝑎𝑎𝑎𝑎 =

∆𝑥𝑥

∆𝑡𝑡

and average acceleration by 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 =

vs. time, and acceleration vs. time graphs.

∆𝑣𝑣

∆𝑡𝑡

. Plot position vs. time, velocity

Questions:

1. For the position vs. time graph:

a) Briefly describe the rough shape of the graph.

b) Theoretically, what physical quantity does the slope represent?

t (s)

x (m)

vave (m/s)

0

0

[no value]

1

2

2

2

4

2

3

6

2

Table 1: sample data for the Figure 1.

aave (m/s2)

[no value]

[no value]

0

0

2. For the velocity vs. time graph:

a) Briefly describe the rough shape of the graph.

b) Theoretically, what physical quantity does the slope represent? What is the instantaneous

velocity of the car at t = 4 s? What is the average velocity of the car in the entire trip? Is

there any difference between average velocity and instantaneous velocity? Why?

3. For the acceleration vs. time graph:

a) Describe the shape of the graph. Is it constant or variable?

B. Constant positive acceleration

Procedure: For this part, you will repeat the same process as part A, however you will define the

initial velocity as 2 m/s and acceleration as 5 m/s2 as shown in figure 2. You will create a new table

in Excel with different values for position, average velocity and average acceleration. Record the

position of the car every second. Keep all the values for the blue car the same as part A. Plot

position vs. time, velocity vs. time, and acceleration vs. time graphs.

Set the variable

as shown in the

figure.

Read these values.

Figure 2: motion of the red car with positive velocity and positive acceleration.

Questions:

4. For the position vs. time graph:

a) Briefly describe the rough shape of the graph.

b) Theoretically, what physical quantity does the slope represent?

5. For the velocity vs. time graph:

a) Briefly describe the rough shape of the graph.

b) Theoretically, what physical quantity does the slope represent? What is the instantaneous

velocity of the car at t = 4 s? What is the average velocity of the car in the entire trip? Is

there any difference between average velocity and instantaneous velocity? Why?

6. For the acceleration vs. time graph:

a) Describe the shape of the graph. Is it constant or variable?

C. Constant negative acceleration

Procedure: For this part, you will repeat the same process as part A, however you will define the

initial velocity as 17 m/s and acceleration as -5 m/s2 as shown in figure 3. You will create a new

table in Excel with different values for position, average velocity and average acceleration. Record

the position of the car every second. Keep all the values for the blue car as part A. Plot position vs.

time, velocity vs. time, and acceleration vs. time graphs.

Set the variable as

shown in the

figure.

Read these values.

Figure 3: motion of the red car with positive velocity and negative acceleration.

Questions:

7. For the position vs. time graph:

a) Briefly describe the rough shape of the graph.

b) Theoretically, what physical quantity does the slope represent?

8. For the velocity vs. time graph:

a) Briefly describe the rough shape of the graph.

b) Theoretically, what physical quantity does the slope represent? What is the instantaneous

velocity of the car at t = 4 s? What is the average velocity of the car in the entire trip? Is

there any difference between average velocity and instantaneous velocity? Why?

9. For the acceleration vs. time graph:

a) Describe the shape of the graph. Is it constant or variable?

10. Without repeating part C can you describe the graphs of position and velocity vs. time if both

initial velocity and acceleration were negative. Please, try to be as specific as possible.

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