9.Extended Response: A box is being pushed across a rough surface. The applied force is increased, and the box starts moving faster. Explain this scenario in terms of balanced and unbalanced forces, friction and net force __ Bonus Questions: 10. A box is being pushed with a force of 50 N to the right, but it does not move Explain why the box remains stationary What can be done to make the box move? 11. You are pulling a sled with a force of 30 N at an angle of 30 degrees above the horizontal. How does the angle of the force affect the normal force and friction acting on the sled?

9. **Balanced and Unbalanced Forces, Friction, and Net Force:**<br /><br />Initially, when the box is at rest despite the applied force, the forces acting on it are balanced. This means the force of static friction (resisting motion) is equal and opposite to the applied force. The net force (the sum of all forces) is zero, and therefore there is no acceleration.<br /><br />As the applied force increases, it eventually overcomes the maximum force of static friction. At this point, the forces become unbalanced. The applied force is now greater than the opposing force of friction (which now becomes kinetic friction, the friction of motion). This unbalanced force results in a net force in the direction of the applied force. According to Newton's Second Law (F=ma), a net force causes acceleration, which is why the box starts moving and speeds up. The greater the net force, the greater the acceleration.<br /><br />**In short:** Balanced forces = no motion. Unbalanced forces = acceleration (change in motion). Friction opposes motion, and the type of friction (static or kinetic) depends on whether the object is moving.<br /><br /><br />**Bonus Questions:**<br /><br />10. **Stationary Box:** The box remains stationary because the applied force of 50 N is not enough to overcome the force of static friction between the box and the surface. The static friction force is equal to or greater than the applied force, resulting in a net force of zero and no motion.<br /><br />**To make the box move:**<br /><br />* **Increase the applied force:** If you push harder than the maximum force of static friction, the box will start to move.<br />* **Reduce friction:** You could reduce friction by using lubricants, placing the box on a smoother surface, or putting rollers underneath it. Reducing friction lowers the force needed to overcome it.<br /><br />11. **Pulling a Sled at an Angle:** When you pull a sled at an angle, the applied force has two components: a horizontal component that pulls the sled forward and a vertical component that pulls upwards.<br /><br />* **Effect on Normal Force:** The upward component of the pulling force partially counteracts the downward force of gravity on the sled. This means the normal force (the force exerted by the surface on the sled, perpendicular to the surface) is *reduced* compared to when the sled is just sitting on the surface or being pulled horizontally. The normal force is equal to the weight of the sled minus the vertical component of the pulling force.<br /><br />* **Effect on Friction:** Since friction is directly proportional to the normal force (friction = coefficient of friction * normal force), a smaller normal force results in *less friction*. Pulling at an angle, therefore, reduces the friction compared to pulling horizontally. This is why it's often easier to pull a sled at an angle.<br />