Foot-pound facts for kids

A foot-pound (written as ft⋅lb or ft⋅lbf) is a unit used to measure work and energy. It belongs to United States customary units and older imperial units. People use it most often in the United States to describe physical actions.

Imagine holding an object that weighs exactly one pound-force. If you lift that object straight up by one foot, you have done one foot-pound of work. This action also uses up one foot-pound of energy. Scientists in most countries measure this same kind of work using the standard SI unit called the joule. One foot-pound equals about 1.356 joules.

Understanding How Foot-Pounds Work

In science, work happens when a force moves an object over a distance. This change in place is called displacement. To find the total work, scientists multiply the strength of the push by the distance traveled.

Energy does not point in any direction. Because of this property, energy is called a scalar. When you do work on an object, you pass energy to it. For example, lifting a toy car onto a shelf gives the toy stored energy. If the toy weighs one pound and the shelf is two feet high, you used two foot-pounds of energy.

Energy Compared to Turning Force

People also use the name foot-pound to describe a twisting effect called torque. While energy and torque sound similar, they are actually different ideas in science. When engineers talk about twisting, they often prefer the term pound-foot.

A twisting effect has a clear direction, so physics describes it as a vector. Mechanics use tools like wrenches to turn a screw or tighten a nut. These metal parts are types of fastener hardware. An automobile engine also creates turning force to spin the wheels. Both concepts come from multiplying feet and pounds, but work involves movement along a line, while torque involves rotation.

How to Convert Foot-Pounds to Other Units

Scientists often need to change foot-pounds into other forms of measurement. Different systems like English engineering units use special math rules to switch between measurements.

Measuring Energy

One foot-pound of energy equals:

• About 1.3558 joules or newton-metres
• About 13,558,179 ergs
• About 0.001285 British thermal units
• About 0.3238 calories
• About 8.46 quintillion electronvolts

Measuring Power

Power tells us how quickly energy gets used up over time. If a machine uses one foot-pound of energy every single second, it produces a specific amount of power.

• One foot-pound per second is about 1.356 watts.
• One horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute.
• One watt equals about 44.25 foot-pounds per minute.

See Also

In Spanish: Pie-libra fuerza para niños

• Conversion of units
• Pound-foot (torque)
• Poundal
• Slug (unit)
• Units of energy