Force is an interaction that changes motion. This guide covers definition, types, units, conversion, measurement, and uses.
What is Force?
Force is a vector that causes acceleration. Newton’s 2nd law: F = m·a. SI unit: newton (N).
Key Concept:
Forces can start/stop/change direction. Balanced forces can still cause stress/deformation.
Types of Forces
Fundamental
- Gravitational
- Electromagnetic
- Strong nuclear
- Weak nuclear
Contact
- Normal
- Friction
- Tension
- Air resistance
- Applied
Non‑contact
- Magnetic
- Electrostatic
- Gravitational
Everyday
- Buoyancy
- Spring
- Drag
- Thrust
- Lift
Units of Force
SI Units
- Newton (N): 1 N = 1 kg·m/s²
- Kilonewton (kN): 1,000 N
- Meganewton (MN): 1,000,000 N
Other Common Units
- Pound‑force (lbf): 4.448 N
- Kilogram‑force (kgf): 9.807 N
- Dyne (dyn): 10⁻⁵ N
- Poundal (pdl): 0.138 N
Force Conversion Table
| Unit | Newtons (N) | Pound‑force (lbf) | Kilogram‑force (kgf) |
|---|---|---|---|
| 1 N | 1 | 0.2248 | 0.102 |
| 1 lbf | 4.448 | 1 | 0.4536 |
| 1 kgf | 9.807 | 2.205 | 1 |
Measuring Force
Spring scales
Hooke’s law extension/compression. Household/fish scales.
Load cells
Strain gauges → electrical signal. Industrial scales/testing.
Piezo sensors
Charge from applied force. Dynamic measurements.
Applications of Force
Engineering
- Structural analysis
- Mechanical design
- Material testing
- Vehicle safety
Sports science
- Biomechanics
- Equipment design
- Performance
- Injury prevention
Manufacturing
- Quality control
- Automation
- Robot feedback
- Packaging tests
Medical
- Prosthetics
- Physiotherapy
- Surgical robotics
- Orthopedic implants
Did You Know?
Strong nuclear force binds nuclei; ~10³⁸× gravity at subatomic scale.
Force in Everyday Life
Common examples
- Typing ~1–2 N
- Hold phone ~2 N
- Pedal ~200–300 N
- Hard braking friction ~3,000 N
Extreme forces
- Shuttle engine ~2.1 MN
- Blue whale bite ~60,000 N
- Break femur ~4,000 N
- Weight of 70 kg person ~686 N
Practical Tip:
Use free‑body diagrams and resolve components along axes for accurate analysis.