3.6 Introduction to Electric Forces

Introduction to Electric Forces

Understanding Forces: Revisiting Newton’s Laws

The study of electric forces builds upon the fundamental principles of Newton’s laws of motion. These laws provide the framework for understanding dynamics:

1. First Law of Motion (Law of Inertia):

   • An object remains at rest or in uniform motion unless acted upon by an external force.

   • Key Concepts:

     • Inertial Mass: Mass in motion.

     • Gravitational Mass: Mass influenced by gravity.

2. Second Law of Motion:

   • Force is directly proportional to acceleration and mass:

3. Third Law of Motion:

   • For every action, there is an equal and opposite reaction. Forces always come in pairs, known as action-reaction pairs.

Electric force at work! Paper sticking to comb!

Electric Forces at Work

Electric forces operate under the same Newtonian principles but involve charged particles. Let’s explore an example:

Example Problem 1:

Scenario: A car moving at 50 km/h brakes to a stop in 5 seconds. What is its acceleration?

Solution:

• Initial velocity .

• Final velocity .

• Time .

• Acceleration .

Convert to :

Substitute:

The acceleration is (deceleration).

History of Electric Forces

After Newton’s groundbreaking work on gravity, attention shifted to electricity. Influential scientists like Benjamin Franklin and Charles-Augustin de Coulomb advanced our understanding of electric charges and forces.

Key Milestones:

1. Ancient Observations:

   • The Greeks noted that amber, when rubbed with fur, attracted small objects (triboelectricity).

2. 16th-17th Centuries:

   • William Gilbert coined the term electricity and explored magnetism.

3. 18th Century:

   • Benjamin Franklin: Demonstrated the nature of electric charge and grounding.

   • Coulomb: Developed Coulomb’s Law:

     • : Electric force.

     • : Charges of particles.

     • : Distance between charges.

     • : Coulomb’s constant, .

4. 19th-20th Centuries:

   • Faraday and Maxwell: Unified electricity, magnetism, and light through the electromagnetic field concept.

Electric Force in Action

Electric forces arise from charged particles interacting with one another. They exhibit:

1. Attractive Forces: Between opposite charges.

2. Repulsive Forces: Between like charges.

Example Problem 2:

Scenario: A ball is thrown upward at 20 m/s. How high does it go?

Solution:

• Initial velocity .

• Final velocity .

• Acceleration due to gravity .

• Use .

Substitute:

The ball reaches a height of .

Key Takeaways

• Electric forces follow inverse square laws, like gravity.

• Coulomb’s Law and Newton’s Laws provide foundational insights.

• The interplay of history and physics has shaped modern electromagnetism.

The journey to understanding electric forces is both historical and scientific, showcasing the elegance and interconnectedness of physics.