Download Newton 2nd Law

Physics 1405: Conceptual Physics I
Name(s)___________________
Newton’s 2nd Law of Motion
Equipment
Air track with accessory box, smart pulley, string, mass hanger with masses.
Discussion
The purpose of this experiment is to investigate Newton's 2nd Law of Motion. A small mass (m) will
hang over a pulley at the end of the airtrack and will pull a cart of mass (M) along the length of the
airtrack. It can be shown from Newton's 2nd Law that the acceleration a is given by the equation:
Equation 1
a=
mg
(M+m)
where mg is the force (weight) on the system that is made up of the cart and hanging mass.
Figure 1
Procedure
1. Set up an airtrack with a smart pulley at one end. Balance the airtrack by turning the air on and
placing the glider in the middle of the airtrack. Adjust the legs of the airtrack so that the glider
barely moves.
2. Ask the instructor or lab attendant how to locate the proper file on the computer for your sensor.
3. Attach the hook accessory to one end of the cart. Balance the cart by adding some other accessory
on the other end of the cart. (See photo in Figure 1). Weigh the cart. Record this in kg.
4. Attach a string (about 1.5 m) to the hook on the cart. Have the string go over the smart pulley and
hang down, ready to be attached to a weight hanger at the other end. Make sure that the string is
parallel to the airtrack.
5. Attach a hanging mass (m) of 0.025 kg to the string. You can use any masses available. Make sure
to measure the hanging masses to be sure they are about 0.025 kg.
6. This step works best with 2 people. One will move the cart backwards until the hanging mass
hanger almost touches the pulley. The other person will click the Collect button (or press Return).
The first person will release the cart. The mass hanger will fall downward and pull the cart across
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the air track. (Catch the cart before it hits the end of the airtrack so that no damage is done.) Click
the Stop button or press Return to stop timing before the mass reaches the end of the track.
7. The computer will then display a set of graphs. Look for the Velocity vs. Time graph. The
slope of this graph is the acceleration of the system. Next, go to Analyze on the menu bar and go
down to Linear Fit. The computer will then display a linear equation from which you can get the
slope. The value of slope is your experimental acceleration.
8. Using equation 1, compute the accepted acceleration. Compare the theoretical acceleration (found
from equation 1) with the actual measured acceleration and calculate a % error.
% Error =
A E
A
x100 =
9. Repeat the entire process with other mass combinations as shown in the Data Section.
DATA
Keep the cart mass the same and change the hanging mass for Parts a) and b).
Part a). Hanging Mass One, m = _______kilograms
Mass of cart, M = ___________ kilograms
Total mass, (M + m) = _____________ kilograms
Net force, mg = ___________Newtons
Accepted acceleration,
mg
= __________m/s2
( M  m)
Experimental acceleration = slope of velocity vs. time graph ____________ m/s2
% Error =
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A E
A
x100 = ___________%
2
Part b). Hanging Mass Two, m = ______kilograms
Mass of cart, M = ___________ kilograms
Total mass, (M + m) = _____________kilograms
Net force, mg = ________ Newtons
Accepted acceleration,
mg
= __________m/s2
( M  m)
Experimental acceleration = slope of velocity vs. time graph ____________ m/s2
% Error =
A E
A
x100 = ___________%
Increase the mass of the cart and then repeat the above procedure for Parts c) and d).
Part c). Hanging Mass, m = _________kilograms
Mass of cart, M = ___________ kilograms
Total mass, (M + m) = _____________ kilograms
Net force, mg = ________ Newtons
Accepted acceleration,
mg
= __________m/s2
( M  m)
Experimental acceleration = slope of velocity vs. time graph ____________ m/s2
% Error =
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A E
A
x100 = ___________%
3
Part d). Hanging Mass, m = _________kilograms
Mass of cart, M = ___________ kilograms
Total mass, (M + m) = _____________ kilograms
Net force, mg = ________ Newtons
Accepted acceleration,
mg
= __________m/s2
( M  m)
Experimental acceleration = slope of velocity vs. time graph ____________ m/s2
% Error =
A E
A
x100 = ___________%
Analysis and Discussion
1. List all the possible source of experimental error. Be specific.
2. In the experiment, should the mass of the string be added to the total mass moved by the
unbalanced force for better accuracy? Explain.
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3. Complete the following sentences:
a. When the unbalanced force increases (total mass remaining constant), the acceleration of
the system __________.
b. When the total mass that is accelerating increases (unbalanced force remaining constant),
the acceleration of the system ___________.
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