Examples of objects in force equilibrium in daily situations.

📚 Quick Study Guide

• ⚖️ Force equilibrium occurs when the net force acting on an object is zero. This means the vector sum of all forces is equal to zero: $\sum \vec{F} = 0$.
• 🍎 An object in force equilibrium will either be at rest (static equilibrium) or moving with constant velocity (dynamic equilibrium).
• 📐 To solve equilibrium problems, it's helpful to draw a free-body diagram showing all forces acting on the object.
• ➕ Resolve forces into their x and y components and apply the equilibrium conditions: $\sum F_x = 0$ and $\sum F_y = 0$.
• 💡 Common forces include gravity ($F_g = mg$), tension ($T$), normal force ($N$), and friction ($f$).

Practice Quiz

1. Which of the following is the best example of an object in static force equilibrium?

   1. A car accelerating down a hill.
   2. A book resting on a table.
   3. A skydiver falling through the air at increasing speed.
   4. A ball rolling down a ramp.

2. A lamp is hanging from the ceiling. What forces are acting on it in equilibrium?

   1. Only tension
   2. Only gravity
   3. Tension and gravity
   4. Tension and normal force

3. A tightrope walker stands still on a rope. What is true about the tension in the rope?

   1. The tension is equal to the walker's weight.
   2. The tension is less than the walker's weight.
   3. The tension is greater than the walker's weight.
   4. The tension is zero.

4. A box is pushed across a floor at a constant speed. What can you say about the forces acting on the box?

   1. The pushing force is greater than the friction force.
   2. The pushing force is less than the friction force.
   3. The pushing force is equal to the friction force.
   4. There is no friction force.

5. What condition must be met for an object to be in equilibrium?

   1. The net force must be non-zero.
   2. The net torque must be non-zero.
   3. The net force and net torque must both be zero.
   4. Only the net torque must be zero.

6. A picture hangs symmetrically on a wall, supported by two strings. If the weight of the picture is 20N, what is the tension in each string (assuming they make the same angle with the vertical and neglecting the string's weight)?

   1. 5 N
   2. 10 N
   3. 20 N
   4. 40 N

7. A person is sitting still in a chair. What force is balancing the gravitational force on the person?

   1. Applied force
   2. Tension force
   3. Normal force
   4. Friction force