What is the difference between torque and force?

Force is a push or pull that creates linear motion, measured in newtons or pounds-force. Torque is rotational force that causes rotation around an axis, measured in newton-meters or foot-pounds. Torque equals force times the distance from the rotation axis.

How do you convert newton-meters to foot-pounds?

Divide newton-meters by 1.356 to get foot-pounds. For example, 100 N·m ÷ 1.356 = 73.7 ft-lbf. To convert foot-pounds to newton-meters, multiply by 1.356.

Why does a longer wrench make bolts easier to loosen?

Torque equals force times lever arm (τ = F × r). A longer wrench provides a longer lever arm, so you need less force to achieve the same torque. Doubling the wrench length halves the force needed.

Torque vs Force

Linear Push vs Rotational Twist

Learn the Difference

Force pushes or pulls in a straight line; torque twists around an axis. A wrench applies force to create torque on a bolt. Understanding the relationship between these concepts is essential for mechanical engineering, automotive work, and physics.

The Fundamental Difference

Force

Creates or changes linear motion
Acts in a straight line
Measured in newtons (N) or pounds-force (lbf)
Example: Pushing a box across the floor

Torque

Creates or changes rotational motion
Acts around an axis
Measured in newton-meters (N·m) or foot-pounds (ft-lbf)
Example: Turning a steering wheel

The Torque Formula

Torque = Force × Lever arm (perpendicular distance)

τ = F × r

Example

A 50 N force applied at the end of a 0.3 m wrench:

τ = 50 N × 0.3 m = 15 N·m

Why Lever Arm Matters

A longer lever arm means more torque with the same force:

50 N × 0.1 m = 5 N·m
50 N × 0.3 m = 15 N·m
50 N × 0.5 m = 25 N·m

Convert Force Units

Torque Units Comparison

Unit	System	Conversion
Newton-meter (N·m)	SI (metric)	1 N·m = 1 N·m
Foot-pound (ft-lbf)	Imperial	1 ft-lbf = 1.356 N·m
Inch-pound (in-lbf)	Imperial	1 in-lbf = 0.113 N·m
Kilogram-force-meter	Metric (non-SI)	1 kgf·m = 9.807 N·m

Converting

N·m to ft-lbf: Divide by 1.356
ft-lbf to N·m: Multiply by 1.356

Practical Applications

Automotive Torque Specs

Application	Typical Torque (N·m)	Typical Torque (ft-lbf)
Spark plug	15-30	11-22
Wheel lug nut	100-150	74-111
Head bolt	50-120	37-89
Oil drain plug	25-40	18-30

Engine Torque

Economy car: 150-200 N·m (111-148 ft-lbf)
Sports car: 400-600 N·m (295-443 ft-lbf)
Heavy truck: 1,500-2,500 N·m (1,106-1,844 ft-lbf)

Force Creates Torque

When you use a wrench:

You apply force (F) to the wrench handle
The force acts at distance (r) from the bolt center
This creates torque (τ = F × r) on the bolt
The bolt rotates (or tightens)

Why Longer Wrenches Are Easier

To achieve 50 N·m torque:

With 0.1 m wrench: Need 500 N force (hard!)
With 0.25 m wrench: Need 200 N force (moderate)
With 0.5 m wrench: Need 100 N force (easy)

Torque vs Power in Engines

Engine specifications list both torque and power:

Torque: The rotational force the engine produces
Power: How fast it can do work (torque × rotational speed)

Power = Torque × Angular velocity

HP = (Torque × RPM) / 5,252 (when torque is in ft-lbf)

High torque at low RPM = good for towing. High power = good for top speed.

Conclusion

Force and torque are related but distinct: force acts linearly, while torque causes rotation. Torque equals force times the perpendicular distance from the rotation axis (τ = F × r). This is why longer wrenches make loosening bolts easier—more lever arm means more torque for the same applied force. Understanding this relationship is fundamental to mechanics, from tightening bolts to understanding engine specifications.

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