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Newtons Second Law of Motion

By Edward Rivera,2014-01-20 02:24
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Newtons Second Law of Motion

    Experiment

     9

    Newton’s Second Law How does a cart change its motion when you push and pull on it? You might think that the harder

    you push on a cart, the faster it goes. Is the cart’s velocity related to the force you apply? Or does

    the force just change the velocity? Also, what does the mass of the cart have to do with how the

    motion changes? We know that it takes a much harder push to get a heavy cart moving than a

    lighter one.

    A Force Sensor and an Accelerometer will let you measure the force on a cart simultaneously

    with the cart’s acceleration. The total mass of the cart is easy to vary by adding masses. Using

    these tools, you can determine how the net force on the cart, its mass, and its acceleration are

    related. This relationship is Newton’s second law of motion.

    Figure 1

    OBJECTIVES

    ? Collect force and acceleration data for a cart as it accelerates on a horizontal surface.

    ? Compare force vs. time and acceleration vs. time graphs.

    ? Analyze a graph of force vs. acceleration.

    ? Determine the relationship between force, mass, and acceleration.

    MATERIALS

    Power Macintosh or Windows PC Logger Pro

    LabPro or Universal Lab Interface low-friction dynamics cart

    Vernier Force Sensor kg mass sets

    Vernier Motion Detector

Physics with Computers 9 - 1

Experiment 9

    PRELIMINARY QUESTIONS (THINK ABOUT YOUR RESPONSES)

    1. When you push on an object, how does the magnitude of the force affect its motion? If you

    push harder, is the change in motion smaller or larger? Do you think this is a direct or inverse

    relationship?

    2. Assume that you have a bowling ball and a baseball, each suspended from a different rope. If

    you hit each of these balls with a full swing of a baseball bat, which ball will change its motion

    by the greater amount?

    3. In the absence of friction and other forces, if you exert a force, F, on a mass, m, the mass will

    accelerate. If you exert the same force on a mass of 2m, would you expect the resulting

    acceleration to be twice as large or half as large? Is this a direct or inverse relationship?

    PROCEDURE

    nd1. Open the Logger Pro Program. The experiment file ( Newton’s 2 Law) is located at

    N;\Courses\Rods

    Physics\Logger pro

    Experments.

    2. Connect a Dual-Range

    Force Sensor to Channel 1

    on the LabPro Connect the

    Motion Probe to Dig/Sonic

    Channel 2

    The Logger Pro Program

    may not automatically

    detect the force probe.

    Click CONNECT and

    make sure the sensor name

    channel is correct.

    3. To get the best

    numerical results in the

    experiment, you will

    calibrate the force sensor

    a. Choose Calibrate

    from the Experiment

    menu.

    b. Click the Force icon that appears in Channel 1.

    c. Click the button.

    d. Remove all weight from the Force Sensor and hold it vertically with the hook pointed

    down.

    e. Type 0 in the Value 1 edit box.

    Keepf. When the displayed voltage reading for Input 1 stabilizes, click .

    g. Add the 0.500 kg (4.9-N) mass to the hook of the Force Sensor.

    h. Type 4.9 in the Value 2 edit box.

    Keepi. When the displayed voltage reading for Input 1 stabilizes, click .

     Keepa. When the displayed voltage reading for Input 2 stabilizes, click , then click .

    9 - 2 Physics with Computers

     Newton’s Second Law

    You should check the calibration by measuring the weight of different masses. Find the mass

    of the cart with the Force Sensor. Record the mass in the data table.

    4. Attach the Force Sensor to a dynamics cart so you can apply a horizontal force to the hook,

    directed along the sensitive axis of your particular Force Sensor. Next, attach the force sensor

    to its holder on the dynamics cart. Attach a string to the force Sensor and be sure it is long

    enough to connect to a slotted mass holder which should be hung over a pulley as shown in

    the figure..

    6. Place the cart on a level surface. Make sure the cart is not moving and click , then click

    .

    Trials

    7. You are now ready to collect force and motion data. Vary the FORCE acting on the cart

    (weight in the mass holder). Do not use too much force or the cart will move too quickly and

    the force calibration will not apply to your range. Protect the floor will a thin object ( an

    English or math text would do nicely-not your wonderful physics text)

    8. Note the shape of the force vs. time and velocity vs. time graphs. Determine the acceleration

    of the cart. Determine the avg force during the interval of the acceleration. Highlight section

    and press “STAT”. Record the Force and acceleration in the data table.

     9. Repeat to determine average Force and acceleration. You should have 3 values of each to

    compute averages.

     10. Use a different force (weight) and repeat. You should have at least 4 different forces

    11. Open Graphical Analysis. Make a graph of Force(y axis) vs Acceleration (x axis).

    Determine if a relationship can be determined.

    DATA TABLE

    Trial I

    Data using cart Mass of Cart =_____kg

     kg Force Acceleration

    Hanging Trial 1 Trial 2 Trial 3 Average Average trial 1 trial 2 trial 3 weight (N) (N) (N) Force (N) acceleration 2222(m/s) (m/s) (m/s) (N) (m/s)

QUESTIONS

    1. What are the units of the slope of the force vs. acceleration graph? Simplify the units of the

    slope to fundamental units (m, kg, s).

    Physics with Computers 9 - 3

Experiment 9

2. What physical quantity does the slope of your Force vs Acceleration graph represent?

3. Describe the relationship between force and acceleration by looking at the GRAPH and

    explaining the line you decided on. How can the line be extrapolated to include VERY

    LARGE Forces (weights)?

4. Write the equation to your graph and whether there is a limitation to it’s useful range.

5. Consider your answer to question 2. Was the physical quantity kept constant? What was

    wrong with the lab procedure here? Was something controlled? Explain.

    6. Is there a discrepancy with what Newton’s 2nd law predicts? Explain why or why not.

Lab report should include one sample of Force vs time and velocity vs time graphs from Logger

    Pro showing average Force “STAT” and acceleration from “SLOPE”. All sections of the LAB REPORT FORMAT should be followed except for the Discussion of

    Results and conclusions. Be sure to copy and paste the questions into your answer document. Be

    sure you answers to the questions above are complete.

    9 - 4 Physics with Computers

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