# Avalanche Patrol Lab

 Materials: Computer and School Network Time Allotment: 3 Class Days

### Purpose:

The purpose of this lab is to investigate the relationship between Newton's second and third laws of motion and the momentum conservation principle; the findings will be related to the interaction between a cannonball and a cannon in an explosion.

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 school network in the usual manner.
• Open the Interactive Physics application.
• Choose Open... from the File menu. Navigate to the Hewitt Simulations folder and open the file titled Avalanche Patrol by double-clicking on its name.

### Situation A:

Maria's job is to develop an easily transportable cannon to be used to blow apart dangerous snow banks that might avalanche. The cannon will be transported on skis, so it cannot be too heavy; yet it needs to be powerful enough to fire a cannonball a long distance. Maria needs to find out how the mass of the cannon affects the recoil and the velocity of the cannonball. Because the cannon is on skis, assume there is no friction to resist the cannon's recoil after it is fired. The mass of the cannonball is 10.00 kg.

### Make a Prediction:

1. Predict how the cannon's mass will affect the strength of its recoil. (The strength of the recoil can be measured in terms of the cannon's acceleration after it is fired). Circle your prediction.

1. The greater the cannon's mass, the stronger the cannon's recoil.
2. The greater the cannon's mass, the weaker the cannon's recoil.
3. The cannon's mass has no effect on the strength of its recoil.

2. Predict how the cannon's mass will affect the velocity of the fired cannonball. Circle your prediction.

1. The greater the cannon's mass, the higher the cannonball's velocity.
2. The greater the cannon's mass, the lower the cannonball's velocity.
3. The cannon's mass has no effect on the cannonball's velocity.

 Run Simulation: Set Cannon mass to 40.00 kg. Set Tree used as brace to No. Click the Run button and observe the simulation. Record the Acceleration of the cannon while it's in the cannon, and record the Velocity of the cannonball after it clears the cannon in Table 1 below. Click the reset button and repeat the above steps with Cannon mass set to 20.00 kg. Click the Reset button and repeat the above steps with Cannon mass set to 5.00 kg.

3. Were your predictions correct? _______ Describe how the cannon's mass affects the cannon's recoil (acceleration) and the cannonball's velocity.

4. Both the cannon and the cannonball experience the same force. Explain why the accelerations and velocities of the cannon and the cannonball are different even though they both experience the same force (the explosion inside the cannon).

5. Apply Newton's third law to the firing of the cannon by identifying the action and reaction forces.

 Run Simulation: Click the Reset button. Set Cannon mass to 20.00 kg. Set Tree used as brace to No. Click the Run button and observe the simulation.

6. Using values from the simulation, record the mass and acceleration of the cannon and cannonball in the spaces provided below. Then, using Newton' second law, calculate the force applied to the cannon and the cannonball.

 Mass of cannon = ________ kg Acceler'n of cannon = ________ m/s2 Mass of cannonball = ________ kg Acceler'n of cannonball = ________ m/s2

1. Now use Newton's second law (Fnet = m*a) to calculate the force applied to the cannon. PSYW

2. Now use Newton's second law (Fnet = m*a) to calculate the force applied to the cannonball. PSYW

3. How are the two forces you calculated above related? _________ Explain.

4. Do your calculations support Newton's third law? _________ Explain.

### Make a Prediction:

7. Assume the cannon and the cannonball both have a mass of 10.00 kg. Predict how having the same mass will affect the accelerations of the cannon and the cannonball.

 Run Simulation Click the Reset button. Set Cannon mass to 10.00 kg. Set Tree used as brace to No. Click the Run button and observe the simulation.

8. Was your prediction correct? ___________ Record the accelerations for the cannon and the cannonball below.

 Acceler'n of cannon = ________ m/s2 Acceler'n of cannonball = ________ m/s2

Explain the results using Newton's second and third laws.

### Situation B:

Maria now braces the cannon against a tree and fires it again to see if it performs any differently. The tree prevents the cannon from recoiling.

### Make a Prediction:

9. Predict the effect which bracing the cannon against a tree will have upon the cannonball's velocity? Circle the correct answer.

1. The cannonball's velocity will be lower.
2. The cannonball's velocity will be the same.
3. The cannonball's velocity will be higher

 Run Simulation: Click the Reset button. Set Cannon mass to 20.00 kg. Set Tree used as brace to Yes. Click the Run button and observe the simulation.

10. On a separate sheet of paper, record the cannonball's velocity with and without using the tree as a brace. Note: Cannon mass is 20.00 kg

1. The cannonball's velocity without using the tree as a brace (from Table 1) = ________ m/s

2. The cannonball's velocity using the tree as a brace (from simulation) = _________ m/s

11. Was your prediction correct? _______ Explain the results using Newton's second and third laws.

### Momentum Analysis:

12. Explosions such as these can be analyzed using the law of momentum conservation. The law states that "In an isolated system, the total momentum of the system before the explosion is equal to the toal momentum of the system after the explosion."

 Run Simulation: Run the simulation several times (using the values given for the cannonball mass and the cannon mass) and use the velocity and mass of the two objects (the cannonball's mass is 10.00 kg) to determine the post-explosion momentum of the individual objects and the entire system. Caution: consider the leftward direction to be the negative direction; thus, the momentum of a leftward moving object would have a negative value.

 Cannon Mass (kg) Braced by Tree? Cannon Velocity (m/s) Cannonball Velocity (m/s) Cannonball Mom. (kg*m/s) Cannon Mom. (kg*m/s) 10.00 No _______ _______ _______ _______ 20.00 No _______ _______ _______ _______ 5.00 No _______ _______ _______ _______ 40.00 No _______ _______ _______ _______ 20.00 Yes _______ _______ _______ _______ 20.00 No _______ _______ _______ _______

13. State the total momentum of the cannon-cannonball system prior to the explosion. __________ Explain your answer.

14. Explain which results (row number) support the law of momentum conservation principle and how they do support it. Use a specific row of the data table to explain specifically how the data supports this principle.

15.The law of momentum conservation does not apply to two of the simulations. Identify which two simulations and explain why the law of momentum conservation cannot be applied for these two simulations.

### Conclusion:

Summarize your findings by discussing how Newton's second and third laws and the momentum of momentum conservation can be applied to the explosion between object 1 and object 2. Be specific in your discussion. Use real numerical values wherever necessary. Do a "bang-up job."