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# Pound|Definition & Meaning

## Definition

**Pound**, abbreviated as lb, is the **unit** of **mass** in the US and **Imperial** measurement systems. Its **SI** counterpart is the **kilogram** (kg), where **1 pound** = 0.45359237 kg = 453.59237 grams. For example, a **longsword** weighs around 3 to 4 pounds.

## What Is a Pound?

A **pound** is an **imperial** unit of estimating the **mass** of any object. It is a unit of **measurement** indicating the **amount** or quantity of matter **occupied** by any object. It tells us whether the thing being measured is **heavy** or light. It is **abbreviated** as ‘lb.’ A **pound** can also be called **pound-mass** (lbm). A pound is a unit of measurement in the **imperial** measuring system.

## Imperial Measuring System

The **Imperial** system is a system of measurement utilized in the **United** **Kingdom** and other Commonwealth **countries**. It includes units like feet, **inches**, ounces, **pounds**, gallons, etc. It is still often used to measure **quantities** like **distance**, weight, length, **area**, volume, etc., in the United Kingdom.

The **imperial** system is also known as the **British** imperial system because it was first defined in the **British** weights and **measures** act in **1824**. This system came into **official** use in the **British** empire in **1826** and is still in use in some parts of the world.

### Why Is the Pound Abbreviated as lb?

The word **pound** comes from **ancient** **Rome,** where they used the term **libra** **pondo** when referring to **weight**. The **Latin** words Libra meant **weight,** and pondo meant **pound**. The word **pound** is shortened from pondo, and the **abbreviation** lb is derived from the part of the word. This is how the word **pound** and its **abbreviation** came into existence.

### What Is Pound Force?

** **It is defined as the **gravitational** force **exerted** on one pound of any mass on the surface of the **earth**. Pound force **accelerates** an object at the rate of 32.174 ft\s^{2}. Figure **32.174** is the standard **acceleration** due to gravity on earth. **Pound** force is abbreviated as **‘lbf.’**

### Mass and Weight

As we are discussing the units of **mass**, we must take into **consideration** the difference between mass and **weight** and their units. **Mass** is the net amount of **matter** that a body has, whereas **weight** is the **force** of **gravity** acting upon an object by the **earth**.

In other words, **mass** is a **quantity** that doesn’t change and remains **constant** without due consideration to the **location,** but weight **varies** as we move from one place to another, i.e., the weight of any **object** on **earth** will be different as compared to the **weight** on mars, but the **mass** remains the same.

**Pound** mass is the unit of mass as it tells the **amount** of matter an object **occupies**. On the other hand, **Pound** force is the unit of **weight** as it includes the **effect** of **gravitational** force when being measured.

## Conversion Between lbm and lbf

If we have the mass of an object in **lbm**, we can **convert** it into weight in **lbf**. There is a simple and easy **method** to convert mass into **weight** if we are given the mass and the **force** of gravity of that specific **location**.

First, we have to find the **weight** in **lbm.**ft\s^{2} by using **Newton’s** **second** **law,** i.e., **f=ma**. Next, we have to **convert** this weight into **mass(lbm)** by using the relationship 1lbm=**32.174 **ft\s^{2}.

Let us consider an example to understand this conversion more **efficiently**.

Suppose the mass of an object is 38 lbm**; estimate** its weight on **mars** if the **gravitational** force on mars is 12.2 ft\s^{2}.

Solving this example, we have mass in **pounds** and **acceleration** due to gravity. First, we use Newton’s second law to find the force of **gravity** in lbm.ft\s^{2}.

**mass **= 38 pounds and **acceleration** due to gravity = 12.2 ft\s^{2}

force=mass × acceleration due to gravity

f = 38 lbm × 12.2ft\s^{2}

**f = 463.6** lbm.ft\s^{2}

Now, convert this value into lbf by using the relation:

1 lbm = 32.174 ft\s^{2}

= 463.6 lbm.ft\s^{2} × 1\ 32.174ft\s^{2}

= 463.6\32.174 lbf

= **14.4** **lbf**

Therefore, the object has a weight of 14.4 lbf on **mars**.

### What Is an Ounce?

An **ounce** is a unit of **measuring** mass in the **imperial** system of **measurements**. Then what is the **difference** between pound and ounce? The difference is that if the object is heavy, its mass is measured in **pounds,** whereas the mass of **lighter** objects is measured in **ounces**.

It is just like **grams** and kilograms in the **metric** system, i.e., grams are used for **lighter-weight** objects, and a kilogram is used for heavier **masses**. An ounce is **abbreviated** as ‘oz.’ The relation between pound and ounce is shown below.

## The Difference Between the Pound and Kilogram

Pound and kilogram are both units of mass, but a pound is an **imperial** unit of measuring mass, whereas a kilogram is a **unit** of mass in the **metric** system. The pound is **derived** from a Latin word, but kilogram is derived from a **Greek** word.

**1 pound** is equal to **0.453 kilograms** which implies that a kilogram is **2.204** times a pound. A **pound** is abbreviated as **lb,** but a kilogram is abbreviated as **kilo** or kg.

## Types of Pounds

There are many kinds of pounds that were in use in the past. Some of them are:

the **Avoirdupois** pound ( equal to 454 grams)

**Troy** pound ( equal to 373.241 grams)

**Tower** pound ( equal to 350 grams)

**Merchant’s** pound ( equal to 437 grams)

**London** pound ( equal to 467 grams)

The most typical of these **pounds** is the **avoirdupois** pound which is legally **accepted** as 454 grams and 0.453 kilograms. The **remaining** pounds were used for measuring **different** quantities in their **respective** time periods.

For example, the troy **pound** was used to measure jewelry, metals, **ornaments**, etc. **Merchants’** pound, as the name indicates, was used for **goods** other than medicine, money, spices, etc. The **London** pound was used in different trading sites.

## Solved Examples of Pound Conversion

### Example 1

A person buys 30 kg of tomatoes for his vegetable shop. How many **pounds **did he buy?

### Solution

We have mass in **kilogram **= 30 kg

To convert it into **pounds**, we use the relation:

1 kg = 2.204 pounds

Multiplying the mass in kg with 2.204:

30kg × 2.204 = 66.12 **pounds**

Hence, the person bought 66.12 **pounds **of tomatoes.

### Example 2

Estimate the **mass **of an object in **lbm **if its weight on the moon is 7 lbf. Also, what will be its weight on earth?

### Solution

We have the weight on the moon of an object = 7lbf.

First, we convert this weight into mass in lbm.ft\s^{2} .(remember that g=32.174ft\s^{2} for earth):

= 7 lbf * 32.174 lbm.ft\s^{2} \ 1 lbf

= 7 * 32.174 lbm.ft\s^{2}

= 225.218 lbm.ft\s^{2}

Next, we use newton’s second law to find mass:

m = f\a

(a=5.32ft\s^{2} for moon)

m = 225.218 lbm.ft\s^{2} \ 5.32ft\s^{2}

m = 42.33 lbm

Hence, the mass of the object is 42.33 lbm.

Now, to find the weight of the object on earth where g=32.174 ft\s^{2}, first we use newton’s second law to find the force of gravity in lbm.ft\s^{2}:

F =ma

= 42.33 lbm * 32.174 ft\s^{2}

= 1361.9 lbm.ft\s^{2}

Now converting this value into lbf:

= 1361.9 lbm.ft\s^{2} *(1 lbf \ 32.174 lbm.ft\s^{2})

= 1361.9 \ 32.174 lbf

= 42.32 lbf

Therefore, the weight of the object on earth is **42.32 lbf**.

*All images are created using GeoGebra. *