# Toy Factory Lab

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

### Purpose:

The purpose of this lab is to apply the principles of center of mass, base of support and equilibrium in order to analyze the stability of an object.

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 Toy Factory I.

### Situation A:

The Acme Toy Company is investigating how the stability of a punching bag is affected by the location of its center of gravity. In the test, a heavy ball strikes the punching bag and knocks the punching bag down. If the punching bag is designed correctly, it will always pop up after being knocked down.

### Make a Prediction:

1. Look at the sketch of the punching bag shown at the right in Figure 1. If the punching bag's center of gravity were located at point A, predict what would happen if the punching bag is hiit by a strong horizontal force as shown. Write your prediction below and explain the reasoning behind it.

 Run Simulation: Set X position of center of gravity to 0.00 cm. Set Y position of center of gravity to 26.00 cm. Click the Run button and observe the simulation.

2. Was your prediction correct? __________ A stable punching bag is one that pops up after being knocked down. Is the punching bag stable or unstable when its center of gravity is located at point A? ____________ Explain.

3. When the punching bag's center of gravity is located at point C (see Figure 1), the process of knocking the bag down will end up raising its center of gravity. Predict how the punching bag will respond to being knocked down. Write your prediction below and explain the reasoning behind it.

 Run Simulation: Click the Reset button. Set X position of center of gravity to 0.00 cm. Set Y position of center of gravity to 2.00 cm. Click the Run button and observe the simulation.

4. Was your prediction correct? __________ Describe the results of the simulation using complete sentences.

5. Define the following terms:

1. unstable equilibrium

2. neutral equilibrium

3. stable equilibrium

6. Which of the center of gravity locations, A, B, C, and D, result is unstable equilibrium? Test by using the following coordinates and running the simulation. Refer to Figure 1. Point B (x = -8.00, y = 26.00) Point D (x = -8.00, y = 2.00)

7. Which of the center of gravity locations, A, B, C, and D, result in stable equilibrium? ___________ Refer to Figure 1. Test by using the following coordinates and running the simulation. Point B (x = -8.00, y = 26.00) Point D (x = -8.00, y = 2.00)

### Situation B

• To prepare for Situation B, open the file titled "Toy Factory II." Use the Open... command from the File menu.

The Acme Toy Company is also developing a toy called the Wonder Wheel. Acme claims the toy wheel defies gravity by rolling uphill. Though made mostly of plastic, the Wonder Wheel owes its special ability to a mass hidden inside the wheel. The hidden mass alters the Wonder Wheel's center of gravity from that of a normal wheel.

 Run Simulation Set Hidden mass to 3.00 kg. Set Show hidden mass? to No. Click the Run button and observe the simulation.

### Make a Prediction

8. Based on your observations, predict where the hidden mass is located in the Wonder Wheel. Show the location of the mass in Figure 2 at the right. Explain in detail using the principles of physics why you chose this location.

 Run Simulation Click the Reset button. Set Hidden mass to 3.00 kg. Set Show hidden mass? to Yes. Click the Run button and observe the simulation.

9. Was your prediction correct? ___________ Does the Wonder Wheel defy gravity? ___________ Explain how the Wonder Wheel works.

10. If given the opportunity, an object will try to obtain the lowest possible position for its center of gravity. Explain how this relates to the Wonder Wheel as it rolls up the incline.

Questions 11-15 are TRUE or FALSE questions related to the speed versus time graph in the simulation. Write a T in the blank space if the statement is TRUE; write an F if it is FALSE.

 ________ 11. The Wonder Wheel is always accelerating. ________ 12. The Wonder Wheel accelerates at a constant rate. ________ 13. Changing the Wonder Wheel's center of gravity would not affect its motion. ________ 14. As the Wonder Wheel rolls up the incline, its center of gravity is moving toward a lower position. ________ 15. During its motion, the speed of the Wonder Wheel is sometimes zero.

### Situation C

The Acme Toy company has another version of the Wonder Wheel that they claim also defies gravity-this version will not roll down an inclined plane! Is this possible? _________ This Wonder Wheel also contains a hidden mass.

 Run Simulation Click the Reset button. Set Hidden mass to 1.50 kg. Set Show hidden mass? to Yes. Click the Run button and observe the simulation.

16. Is the Wonder Wheel defying gravity when it doesn't roll down the inclined plane? __________ Explain the results.

### Conclusion:

In a short paragraph, summarize the principles of balance and equilibrium by describing why one object may be stable and another may not.

### Extension:

This unit has focused on principles of stability - i.e., physical laws which govern whether or not an object will balance. In an effort to internalize these concepts, pick a toy or model which illustrates these principles of stability. Describe the toy or model which you have identified; discuss what physical laws govern whether or not any object is balanced or unstable; apply these physical laws to the toy or model which you have identified in order to explain how the toy or model illustrates the principles of stability. Write clearly using complete sentences. If necessary, use a diagram to support your writing.