7. Select the "Sum of Forces" box. The sum appears in green above the crate. Push the crate until it starts moving again. What is the sum just before and just after is starts moving? (Don't need a value for the 'after' case, just describe the vector. 8. Bring the crate against one wall and push it the other way enough that it keeps moving even after you let it go. While the crate is still moving is there still a net force? If so, what is it and what does it cause the crate to do?

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UpStudy AI · Accepted Answer

Sure, I'd be happy to help you understand and answer these questions.

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**7. Sum of Forces Just Before and Just After the Crate Starts Moving**

- **Just Before the Crate Starts Moving:**
  
  - **Sum of Forces:** *Zero net force.*
  
  - **Explanation:** When you push the crate but it hasn't started moving yet, the forces acting on it are balanced. Specifically, the applied force you're exerting is being exactly countered by the static friction force between the crate and the surface. This balance means that the **sum of all forces** acting on the crate is **zero**. The vectors of the applied force and static friction are equal in magnitude but opposite in direction, effectively canceling each other out.

- **Just After the Crate Starts Moving:**
  
  - **Sum of Forces:** *Net force equals the applied force minus kinetic friction.* 
   
  - **Vector Description:** The **net force** is in the **direction of the applied push**.
  
  - **Explanation:** Once the crate starts moving, static friction is replaced by kinetic friction, which is typically slightly less than static friction. At the instant the crate begins to move, the **applied force** you're exerting is now greater than the **kinetic friction** resisting the motion. Therefore, there is a **net force** in the direction you're pushing. This net force causes the crate to **accelerate** in the direction of the applied force.

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**8. Net Force While the Crate Is Moving After Being Pushed Against a Wall**

- **Is There Still a Net Force?**
  
  - **Net Force:** *Yes, there is still a net force while the crate is moving.*
  
- **What Is It and What Does It Cause the Crate to Do?**
  
  - **Description of the Net Force:** The net force is the **residual applied force** you've exerted minus the **kinetic friction** opposing the motion.
  
  - **Effect on the Crate:** This **net force** causes the crate to **continue moving** or, if the net force is consistent, it can lead to **constant velocity** provided that the forces remain balanced in that direction. If you push harder, increasing the net force, the crate will **accelerate** in the direction of the push. Conversely, if the net force decreases, the crate's **acceleration** will change accordingly. However, if you stop pushing altogether, the net force becomes zero (only kinetic friction acts), and the crate will eventually **decelerate** and come to a stop due to friction.

- **Additional Consideration:** If the crate is moving against one wall and you push from the opposite side, maintaining a **constant velocity** implies that the **applied force** equals the **kinetic friction**. In this scenario, the **net force** is **zero**, and according to Newton's First Law of Motion, the crate will continue to move at a **constant velocity**. However, if you're still applying a force that **exceeds** the frictional force, the crate will **accelerate**.

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**Summary:**

- **Just Before Moving:** Net force is zero (forces are balanced).
- **Just After Moving:** Net force is in the direction of the push (causing acceleration).
- **While Moving Against a Wall:** If you maintain a push that exactly balances kinetic friction, net force is zero (constant velocity). If the push exceeds kinetic friction, there is a net force causing acceleration; if it's less, the crate will decelerate.

Feel free to ask if you need further clarification on any of these points!
**7. Sum of Forces Just Before and After the Crate Starts Moving** - **Just Before Moving:** - **Sum of Forces:** Zero net force (forces are balanced). - **Just After Moving:** - **Sum of Forces:** Applied force minus kinetic friction (net force in the direction of the push, causing acceleration). **8. Net Force While the Crate Is Moving After Being Pushed Against a Wall** - **Is There Still a Net Force?** - Yes, there is a net force while the crate is moving. - **What Is It and What Does It Cause the Crate to Do?** - **Net Force:** Applied force minus kinetic friction. - **Effect:** Causes the crate to continue moving or accelerate in the direction of the push. **Summary:** - **Before Moving:** Forces are balanced (net force = 0). - **After Moving:** Net force is in the direction of the push (causes acceleration). - **While Moving Against a Wall:** - If push balances kinetic friction, net force = 0 (constant velocity). - If push exceeds friction, net force causes acceleration. - If push is less than friction, crate decelerates.

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