# The Sling Lab

 Materials: School Network and Macintosh Computer w/Interactive Physics Time Allotment: 3 Class Days

### Purpose:

The purpose of this lab is to analyze the motion characteristics of an object moving in a circle.

This lab must be done on a Macintosh computer connected to the school network or upon a computer in the Science Computer Lab. To prepare for the lab, do the following steps.

• Log onto the computer in the usual manner.
• Open the Interactive Physics application.
• Open the file titled The Sling.

### Situation A:

At school Sue learned that objects can be thrown a long distance by using a sling. To verify this, she made her own sling by tying a ball to the end of rope. Starting with the ball dangling from the rope, she begins twirling the rope, accelerating the ball in the tangenital direction for a period of 0.50 s. After this period of tangenital acceleration, the ball maintains a constant speed, traveling with a circular path in a horizontal plane above Sue's head until she releases the rope. Note: In this figure and in the simulation you are looking vertically downward on Sue and the twirling ball.

### Make a Prediction:

1. Sue needs to find out how to aim the sling. Predict the path of the ball after it is released. See the sketch above. Note: The ball is traveling a circular path in a horizontal plane above Sue's head before it is released. Place a check mark next to your prediction.

1. The ball will curve inward after its release. Path A
2. The ball will travel in a straight line after its release. Path B
3. The ball will curve outward after its release. Path C

 Run Simulation: Set the Vector Display to off. Click the Tracking On button. Click the Run button and observe the simultaion.

2.Was your prediction correct? Describe the path of the ball after its release.

3.When we look only at the horizontal motion of the ball after its release, what forces act on the ball? _________________ Explain the ball's path using Newton's first law - the law of inertia.

4. Why does the tension in the rope increase as the speed of the ball increases? Explain.

5.Define centripetal force, indicate its direction and describe how centripetal force plays a part in the motion of the ball as it is being twirled in a circle.

 Run Simulation: Click the Reset button. Set the Vector Display to On. Click the Tracking On button. Click the Run button and observe the simulation. Note: Two vectors will appear. The velocity vector is labeled with a V. The acceleration vector is labeled with an A.

6. Describe the acceleration vector (e.g., direction, manitude, etc.) from the time after the speed of the ball becomes constant to the time just prior to when the ball is released.

7. How does the acceleration vector change after the ball is released (comment on both direction and magnitude)? Explain why this happens.

8. Describe what happens to the velocity vector after the ball is released. Explain why this occurs.

9. During the first 0.50 s, the direction of the acceleration vector changes from pointing along with the path of the ball to a direction perpendicular to the path of the ball. Explain why this occurs.

### Conclusion:

Summarize this lab by describing the motion of an object that moves in a circle. Include the following words in your description.

 Centripetal Acceleration Force Velocity Inertia