⚖️ Newton's Third Law Calculator
Calculate action and reaction forces
Enter positive for direction (negative will be calculated)
How to Use This Calculator
Enter the Action Force
Input the magnitude of the action force in Newtons (N) in the input field. You can enter either a positive or negative value to indicate direction. For example, if a person pushes a wall with 100 N to the right, enter 100.
Click Calculate
Press the "Calculate" button to compute the reaction force. The calculator will automatically determine the equal and opposite reaction force based on Newton's Third Law.
Review Results
The results will show both the magnitude of the reaction force and its direction. The reaction force will have the same magnitude as the action force but in the opposite direction.
Formula
F_action = -F_reaction
|F_action| = |F_reaction|
Newton's Third Law Statement
For every action, there is an equal and opposite reaction. This means that whenever object A exerts a force on object B, object B simultaneously exerts an equal and opposite force on object A.
Formula Explanation
- F_action: The force exerted by object A on object B (in Newtons)
- F_reaction: The force exerted by object B on object A (in Newtons)
- The negative sign indicates opposite direction
- The magnitudes are always equal: |F_action| = |F_reaction|
Worked Examples
Example 1: Person Pushing a Wall
If a person pushes a wall with a force of 100 N:
F_action = 100 N
F_reaction = -100 N (wall pushes back with equal force)
|F_reaction| = 100 N
Example 2: Book on a Table
A book weighing 5 N rests on a table:
F_action = 5 N (book's weight down)
F_reaction = -5 N (table's normal force up)
|F_reaction| = 5 N
Example 3: Rocket Propulsion
A rocket engine exerts 10,000 N downward:
F_action = -10,000 N (exhaust gases)
F_reaction = 10,000 N (rocket moves up)
|F_reaction| = 10,000 N
Frequently Asked Questions
What is Newton's Third Law?
Newton's Third Law states that for every action, there is an equal and opposite reaction. When two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction.
Why do the action and reaction forces cancel out if they're equal and opposite?
They don't cancel out because they act on different objects. The action force acts on object B, while the reaction force acts on object A. Since they act on different objects, they don't cancel each other out.
Can I use negative values for the action force?
Yes, you can enter negative values to indicate direction. The calculator will correctly compute the reaction force with the opposite sign. The magnitude will always be the same regardless of the sign.
What are some real-world examples of Newton's Third Law?
Common examples include: walking (you push the ground backward, ground pushes you forward), swimming (you push water backward, water pushes you forward), rocket propulsion (exhaust gases push down, rocket moves up), and a book resting on a table (book pushes down, table pushes up).
How is this different from Newton's First and Second Laws?
Newton's First Law describes inertia (objects at rest stay at rest). Newton's Second Law relates force, mass, and acceleration (F = ma). Newton's Third Law describes how forces always come in pairs between interacting objects.
What units should I use for the force?
The calculator uses Newtons (N) as the standard unit for force. 1 Newton equals 1 kg·m/s². If you have forces in other units (like pounds-force), convert them to Newtons first.
About Newton's Third Law Calculator
Newton's Third Law Calculator is a powerful tool that helps you understand and calculate action-reaction force pairs, one of the fundamental principles of classical mechanics. This calculator demonstrates the principle that for every action, there is an equal and opposite reaction.
When to Use This Calculator
- Analyzing forces in physics problems involving two interacting objects
- Understanding rocket propulsion and jet engine mechanics
- Calculating contact forces between objects (book on table, person on floor)
- Solving problems involving collisions and momentum conservation
- Studying propulsion systems in vehicles and aircraft
Why Use Our Calculator
- Instant calculation of reaction forces from action forces
- Clear visualization of force magnitudes and directions
- Educational tool with detailed explanations and examples
- Free to use with no registration required
- Mobile-friendly interface for calculations on the go
- Accurate results based on established physics principles
Common Applications
- Rocket Science: Understanding how rockets propel themselves by expelling exhaust gases
- Sports: Analyzing how athletes push off surfaces to generate forward motion
- Engineering: Designing structures that must handle equal and opposite forces
- Transportation: Understanding propulsion in vehicles, boats, and aircraft
Tips for Using This Calculator
- Remember that action and reaction forces act on different objects
- Use positive values for one direction and negative for the opposite
- The magnitude of reaction force always equals the magnitude of action force
- Consider both magnitude and direction when analyzing force pairs
- This principle applies to all types of forces: contact, gravitational, electromagnetic, etc.