Download Lab: Applications of Newton`s Second Law of Motion Purpose: To

Lab: Applications of Newton’s Second Law of Motion
Purpose: To investigate the relationship between force and acceleration mathematically, then using an Atwood
machine verifying our calculations.
Equipment:
1 Atwood machine
1 Sonic Ranger
14 10g masses
Name: _______________________
Lab Partners: _______________________
_______________________
_______________________
REMOVE THIS COVER SHEET FROM THE LAB PACKET AND REPORT ALL DATA COLLECTED
USING THE TABLES BELOW
Weight = mass x 9.8m/s2
Trial
Mass block
1
Weight block 1
Mass block 2
Weight block
2
Mass
difference
1
2
3
4
Trial
1
2
3
4
acceleration
calculated
acceleration
experimental
Difference
calculated - experimental
Applications of Newton’s 2nd Law:
Procedure:
1. Set-up the Atwood machine as
illustrated in the diagram below.
2. In the space provided below, create free body diagrams that illustrate all the
forces acting on the hanging masses.
FT
FT
+
+
70 kg
70 kg
Fm1g
Fm2g
3. Describe your observations using appropriate vocabulary.
Student answers should indicate that the forces acting on the system are balanced so there is no acceleration.
4. Using Newton’s second law, write an equation that shows the net forces acting on the system. Remember to
determine the net forces acting on each side of the Atwood Machine first. Also calculate the acceleration of the
system. The equation should match your description from number 3 and your free body diagram.
∑ F = ma
- Fm1g + FT – FT + Fm2g = a(m1 + m2)
-0.686N + 0.686N = a(0.140kg)
0N /0.140kg = a
a = 0 m/s2
5. Next, make a prediction about what would happen if you were to increase the mass on one side of the Atwood
machine. (i.e. take a 10-gram mass from the right side and add it to the left side)
Student answers should indicate that by increasing the mass on one side, the net forces are no longer balanced.
This will lead to an acceleration of the system.
6. Visualize the system and draw another set of free body diagrams to illustrate what the system will look like.
FT
FT
+
+
Fm1g
Fm2g
7. Using Newton’s second law, write an equation that shows the net forces acting on the system. Remember to
determine the net forces acting on each side of the Atwood Machine first. Also calculate the acceleration of the
system. The equation should match your description from number 5 and your free body diagram.
∑ F = ma
- Fm1g + FT – FT + Fm2g = a(m1 + m2)
-0.784N + 0.588N = a(0.140kg)
-0.196N /0.140kg = a
a = -1.40 m/s2
8. You now have a theoretical model of how your system should behave. Now transfer one 10g mass from one
side of the Atwood Machine to the other. Pull the smaller set of masses down so that the larger set is as high as
the string will allow. Use the sonic ranger and data logger to measure the acceleration of the larger set of
masses. Be sure to press the collect button on the data logger problem before you release the larger set of
masses. Record your data.
9. How does your measured value compare to your calculated value? If there are differences, try to account for
them. How could you eliminate the difference?
Answers will vary but should either show a very close comparison between calculated and measured values or
values that are substantially different which is indicative of experimental errors. An example of an experimental
error the sonic ranger detecting motion other that the falling masses.
10. Add another 10 grams to the side that you already increased the mass on. Make a prediction about what should
happen next, will the acceleration be the same? Explain why or why not.
Student responses should indicate that the forces acting on the system will now be out of balance and that an
acceleration will result.
11. Draw free body diagrams for the system.
FT
FT
+
+
Fm1g
Fm2g
12. Using Newton’s second law, write an equation that shows the net forces acting on the system. Remember to
determine the net forces acting on each side of the Atwood Machine first. Also calculate the acceleration of the
system. The equation should match your description from number 10 and the free body diagram.
∑ F = ma
- Fm1g + FT – FT + Fm2g = a(m1 + m2)
-0.822N + 0.490N = a(0.140kg)
-0.392N/0.0140kg = a
a = -2.80 m/s2
13. You now have a theoretical model of how your system should behave. Next set up the sonic ranger so that it
can log the motion of your system. Use the data logging software to measure the acceleration of the system.
Record your data.
14. How does your measured value compare to your calculated value? If there are differences, try to account for
them. How could you eliminate the difference?
Answers will vary but should either show a very close comparison between calculated and measured values or
values that are substantially different which is indicative of experimental errors. An example of an experimental
error the sonic ranger detecting motion other that the falling masses.
15. Add another 10g to the machine (again to the side that you have already been loading). Make a prediction about
what should happen next, will the acceleration be the same? Explain why or why not.
Student responses should indicate that the acceleration would be greater because of a greater imbalance of the
forces acting on either side of the system.
16. Draw a free body diagram of the system.
FT
FT
+
+
Fm1g
Fm2g
17. Using Newton’s second law, write an equation that shows the net forces acting on the system. Remember to
determine the net forces acting on each side of the Atwood Machine first. Also calculate the acceleration of the
system. The equation should match your free body diagram.
∑ F = ma
- Fm1g + FT – FT + Fm2g = a(m1 + m2)
-0.980N + 0.392N = a(0.140kg)
-0.588N/0.014kg = a
a = -4.2 m/s2
18. You now have a theoretical model of how your system should behave. Next set up the sonic ranger so that it
can log the motion of your system. Use the data logging software to determine the acceleration of the system.
Record your data.
19. How does your measured value compare to your calculated value? If there are differences, try to account for
them. How could you eliminate the difference?
Answers will vary but should either show a very close comparison between calculated and measured values or
values that are substantially different which is indicative of experimental errors. An example of an experimental
error the sonic ranger detecting motion other that the falling masses.
20. From your results make a statement about what happens to the acceleration of a system as the net force acting
on the system changes.
Student responses should indicate an understanding that as the forces acting on an object increases so does the
acceleration of the object.
21. In reflection, discuss the impact that Newton’s second law has on your everyday life. For example, the Atwood
machine is essentially a pulley; can you think of any examples of a pulley and relate how Newton’s second law
applies to its function?
Student responses will vary but should include at least one example of a pulley and some understanding of how
Newton’s second law applies to it.
Write your reflection on the back of this page.