Static Equilibrium Bridge Builder
Analyze a simply supported beam with movable load. Calculate support reactions NA and NB using ΣF=0 and Στ=0 equilibrium conditions.
WHAT IS STATIC EQUILIBRIUM?
An object is in static equilibrium when it remains at rest, meaning both its linear and angular accelerations are zero. This requires two conditions to be met: the vector sum of all external forces must be zero (), and the vector sum of all external torques about any axis must be zero (). In AP Physics 1, we often analyze bridges or beams supported at two points to solve for unknown support forces.
HOW TO USE THIS VISUALIZATION
1. **Place Loads on the Bridge**: Drag weights to different positions on the bridge deck. 2. **Observe Support Forces**: Watch how the upward normal forces at the left and right supports change to maintain equilibrium. 3. **Test Torque Balance**: Move a weight closer to one support and notice how that support carries more of the load. 4. **Verify Calculations**: Sum the upward forces and compare them to the total downward weight to verify .
CORE FORMULAS
AP EXAM CONNECTION
Unit: Unit 5: Torque and Rotational Dynamics (Topic 5.1)
Learning Objective: 5.1.2
COMMON MISCONCEPTIONS
- Thinking that is enough for equilibrium (it doesn't prevent rotation).
- Choosing the wrong pivot point for torque calculations (any point works, but some make math easier).
- Neglecting the weight of the bridge itself (it acts at the center of mass).
KEY TAKEAWAYS
- Static equilibrium requires both zero net force and zero net torque.
- Torque balance can be calculated about any pivot point.
- Support forces adjust based on the position of loads relative to the supports.
- The weight of the structure itself acts at its center of mass.
PRACTICE QUESTIONS
Q1 (QUANTITATIVE): A uniform 10 m bridge weighs 1000 N. A 500 N car is 2 m from the left support. What is the force on the right support?
Show Answer & Explanation
Answer: 600 N
Explanation: Sum torques about the left support: N.
