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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

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.

numerical results in the

experiment, you will

calibrate the force sensor

a. Choose Calibrate

from the Experiment

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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