Physics Laboratory

Atwood’s Machine Smart TimerTM Laboratory

Objective: The purpose of this lab is to study the relationship between force, mass, and acceleration using an Atwood’s Machine apparatus.

Introduction: In an Atwood’s machine, the difference in weight between the two hanging masses determines the net force acting on the system. This net force accelerates both of the hanging masses, the heavier mass is accelerated downward, and the lighter mass is accelerated upward.

Procedure: 1. Set up the apparatus as shown below. Use a piece of thread about 10 cm longer than the distance from the top of the pulley to the floor. You can fasten the mass hangers to the thread by wrapping 4-5 turns around the notched area. NOTE: You can choose to use the hanging masses provided instead of the mass hanger and slotted masses. Connect the pulley to the SMART TIMER. Plug in and turn on the SMART TIMER. Physics Laboratory

2. Place about 100 grams of mass on one end of the string or hanger and record the total mass as m1 in the Table. Be sure to include the weight of the hanger if one is used. Place slightly more than 100 grams on the other hanger. Record this total mass as m2.

3. Move the heavier of the two masses upward until the smaller mass almost touches the floor. With the mass motionless and the pulley position so that the red LED on the pulley is OFF, select “Acceleration” for the measurement then “Linear Pulley” for the mode.

4. Press the “Start/top” button and release the heavier mass, which will fall downward, pulling the lighter mass. Stop the pulley just before the heavier mass reaches the floor and press the “Start/Stop” button to halt the timing process.

5. Record the Experimental Acceleration in your table. The units will be in cm/s2.

6. Change the relationship between m1 and m2 by removing mass from one hanger or thread to the other. This allows you to change the net force without changing the total mass. Repeat steps 3-5 at least 5 times using different combinations of m1 and m2. Record all your data in the Table.

7. Now change the total mass, yet keep the net force the same as in one of your first 5 runs (just set up the masses as in one of your earlier runs, then add the same additional mass to both sides). Record your new m1 and m2 values, and the accelerations you obtain. Repeat 3-5 times, each time changing the total mass while keeping the net force the same.

Analysis:  Calculate the net force for each situation, which is the difference between the two masses times the acceleration of gravity: (m1 - m2)g.  Calculate the total mass for each trial, (m1 + m2).  Calculate the theoretical acceleration using Newton’s Second Law: Fnet = ma.  Compare the actual acceleration with the theoretical acceleration by determining the % difference.

My Calculations: Physics Laboratory

Data Table:

Trial m1 m2 Experimental Net Total Theoretical % Diff. ( ) ( ) Acceleration Force Mass Acceleration ( ) ( ) ( ) ( ) 1

2

3

4

5

6

7

8

9

10