Breaking down forces for free body diagrams | AP Physics 1 | Khan Academy

Introduction

This tutorial will guide you through the process of creating free body diagrams, especially when dealing with forces applied at angles. Understanding how to break down forces into their horizontal and vertical components is essential in AP Physics and helps in solving various physics problems effectively.

Step 1: Understand Free Body Diagrams

• A free body diagram (FBD) is a visual representation used to show all the forces acting on an object.
• In an FBD, the object is typically represented as a box or point, and arrows are used to indicate the direction and magnitude of forces acting on it.

Tips

• Always include all forces acting on the body, including gravitational, normal, frictional, and applied forces.

Step 2: Identify Forces Acting on the Object

• List all the forces acting on the object. Common forces include:
  • Gravitational force (weight)
  • Normal force (support force from a surface)
  • Frictional force (resistance to motion)
  • Applied force (force exerted by a push or pull)

Practical Advice

• Pay attention to the context of the problem to identify all relevant forces.

Step 3: Draw the Free Body Diagram

1. Sketch the object as a simple box or dot.
2. Draw arrows to represent each force.
   • The length of the arrow should reflect the magnitude of the force.
   • The direction of the arrow should indicate the direction of the force.

Common Pitfalls

• Ensure that the arrows are accurately placed according to the forces' directions. Misplacing arrows can lead to incorrect conclusions.

Step 4: Break Down Angled Forces

• When a force is applied at an angle, you need to resolve it into horizontal and vertical components using trigonometry.

How to Find Components

1. Identify the angle of the force with respect to the horizontal.
2. Use the following formulas:
   • Horizontal component ( F_x = F \cdot \cos(\theta) )
   • Vertical component ( F_y = F \cdot \sin(\theta) )

Example

• If a force of 10 N is applied at an angle of 30 degrees:
  • ( F_x = 10 \cdot \cos(30) )
  • ( F_y = 10 \cdot \sin(30) )

Step 5: Update the Free Body Diagram with Components

• Replace the angled force in your FBD with its horizontal and vertical components.
• Each component should be drawn as separate arrows emanating from the same point.

Conclusion

Creating free body diagrams is a crucial skill in physics that helps visualize the forces acting on an object. By breaking down forces into their components, especially when applied at angles, you can simplify complex problems. To further enhance your understanding, practice drawing FBDs with varying forces and angles, and solve related physics problems using these diagrams.