Physics Lab 02

PHY 171A Lab 2

Newton’s Second Law of Motion Purpose To determine the relationship between net force, mass, and acceleration and to use vector addition to determine the net force on an object. Apparatus Computer, Atwood’s Machine simulation available at http://www.physicsclassroom.com/Physics- Interactives/Newtons-Laws/Atwoods-Machine Introduction Newton’s second law states that the net force applied to a system of objects equals the mass of the objects times their acceleration. In this lab, you will investigate this law using a simulation of a modified Atwood’s machine. In this machine, the applied force is the weight of the hanging block. Because the blocks are connected by a string, that force accelerates both blocks at the same rate. Two situations will be explored during your lab: a constant applied force and a constant mass of the system. Open the link above and read the information and instructions. Open the interactive and explore the different options. Then follow the procedure below. Note that there are three sizes of each type of object. The small objects are all 1.0 kg in mass, the middle objects are all 2.0 kg in mass, and the large objects are all 3.0 kg in mass. Procedure and Calculations

Constant Applied Force

1. Select the small blue mass and the small red, wheeled cart. If needed, move the cart as far to the left as possible, then click the start button. Record the masses, time, and distance in Data Table 1.

2. Replace the small cart with the medium-sized cart and click the start button. Record the masses, time, and distance for this run in Data Table 1.

3. Replace the medium-sized cart with the large cart and click the start button. Record the masses, time, and distance for this run in Data Table 1.

4. For each run, calculate the acceleration from the distance and time using the equation below and record it in Data Table 1. Show your work for one example.

5. For each run, calculate the total mass by adding the mass of the hanging object to the mass of the cart and record it in Data Table 1. Show your work for one example.

6. For each run, calculate the applied force using the equation below and record it in Data Table 1.

7. Calculate the applied force, the weight of the known mass of the hanging object. Recall that g = 9.8 N/kg. Show your work.

8. Calculate the average value of the applied force from each run. Show your work.

9. Calculate the percent difference between the average value you calculated and the weight of the hanging mass.

Data Table 1

Hanging Mass

Cart Mass Total Mass Time Distance Acceleration Calculated Force

Constant Mass of System

10. Select the small blue mass and the large red, wheeled cart. If needed, move the cart as far to the left as possible, then click the start button. Record the masses, time, and distance in Data Table 2.

11. Replace the small mass with the medium-sized blue mass and replace the large cart with the medium-sized cart, then click the start button. Record the masses, time, and distance for this run in Data Table 2.

12. Replace the medium-sized mass with the large blue mass and replace the medium-sized cart with the small cart, then click the start button. Record the masses, time, and distance for this run in Data Table 2.

13. For each run, calculate the acceleration from the distance and time using the equation below and record it in Data Table 2. Show your work for one example.

14. For each run, calculate the applied force, the weight of the known mass of the hanging object, and record it in Data Table 2. Recall that g = 9.8 N/kg. Show your work.

15. For each run, calculate the mass of the system using the equation below and record it in Data Table 2.

16. Calculate the average value of the total mass from each run. Show your work.

17. Calculate the percent difference between the average value you calculated the total mass of the system, 4.0 kg.

Data Table 2

Hanging Mass

Cart Mass Time Distance Acceleration Applied Force

Calculated Mass

Discussion 1. In the situation with a constant applied force, how did the acceleration change when the total

mass was increased? Is the consistent with Newton’s second law? Explain.

2. In the situation with a constant total mass, how did the acceleration change when the applied force was increased? Is the consistent with Newton’s second law? Explain.

3. Open the interactive simulation again if needed and select the small blue mass and the

small red block. Click the start button. Is the acceleration of this system greater or less than the acceleration of the system with the small blue mass and the small wheeled cart? How do you know? What would cause this difference?