Demonstration of Newton's Second Law by Using Atwood Machine
The Atwood machine illustrates some aspects of force and acceleration. Like an incline, the Atwood machine slows acceleration down to a measurable and observable amount. This project shows how the Atwood apparatus can be used to study acceleration.
What You Need
- support for pulley, such as a ring stand
- various masses
- Set up the apparatus with each of two masses attached to string and suspended over a pulley, as shown in Figure 31-1.
- Release the masses and observe/measure their motion.
- As in previous experiments, the acceleration of the masses can be measured using the stopwatch method (using a = 2d/t2) or determining the acceleration using a motion sensor. (Different combinations of masses can also be compared and ranked visually without detailed measurements.)
The greater the difference between the two masses, the greater the acceleration.
The greater the combined masses, the smaller the acceleration.
The acceleration for the two masses is:
If m1 is the larger mass, the acceleration is in the direction of the larger mass going down.
Why It Works
The force on the system is F = g(m1 – m2). According to Newton's second law, this equals the total mass times the acceleration. Because the total mass is (m1 = m2), we can derive the previous expression for acceleration.
Other Things to Try
Once you get the idea of this, try it at an incline, as shown in Figure 31-2.
Predict what angle or combination of masses will result in equilibrium.
Because friction helps establish stability, a window is around the predicted conditions that will also result in equilibrium. This can also be done with each of the two masses sliding on an incline.
An Atwood machine demonstrates the principles of Newton's second law. The net force on the masses causes the total mass of the system to accelerate.
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety.