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## 4th grade

### Course: 4th grade > Unit 14

Lesson 1: Estimating mass# Choose pounds or ounces to measure weight

Sal discusses US customary units of mass or weight such as ounce, pound, and ton. Created by Sal Khan.

## Want to join the conversation?

- What does a atom weigh?(14 votes)
- An atom is so small that normal measurement units like "grams" or "ounces" don't really make sense. You can use them, but it's like trying to measure the length of your cat in kilometers; you end up with a very tiny number that's hard to picture. Scientists actually use a special unit called the "atomic mass unit" (shortened to u) to measure atoms. So for instance one Carbon atom is 1u, and a heavier Uranium atom is about 238u.(17 votes)

- Can anyone explain me these units like pounds, ounces, yards and gallons? I only know the metric system. We don't use these other units in India.(9 votes)
- These are all units part of the Customary System in the United States, also known as the Imperial System by people who use the metric system. Khan Academy is originally an American company, so they use this system. Pounds and ounces are kind of like grams and kgs in other countries. They are used to measure weight and mass. 16 ounces make a pound, and 2,000 pounds make a ton (not to be confused with tonne, which is in the metric system). Yards, inches, miles, and feet are kind of like meters and centimeters. They are used to measure distance. 12 inches equal to one foot, 3 feet are equal to one yard, and 5280 feet, or 1760 yards. Gallons, pints, cups, and fluid ounces (not to be confused with regular ounces) are used to measure volume, kind of like liters (litres) and milliliters (millilitres). 2 cups equal one pint, 2 pints equal one quart, and 4 quarts equal 1 gallon. For more information, you can use the google converter tool to help.(15 votes)

- does a truck weigh 2 tons

or 2.5 tons?

(note that 2.5 is 5/2 or 2 1/2).(5 votes)- it is 2 1/2 and 5/2 because say 1 is 2/2 so 4/2 is 2 and add 1/2 to 4/2 = 5/2 = 2 1/2 do you get me? if so happy to help.(6 votes)

- Do they have questions for each single vid? I’m so confused🧐(5 votes)
- yes he he he he he(2 votes)

- Are lb heavier then kilograms?(4 votes)
- No. A pound (lb) is about 454 grams, while a kilogram is 1,000 grams. So actually a kilogram is heavier than a pound (on Earth's surface).

Have a blessed, wonderful day!(2 votes)

- up vote me i up vote u(4 votes)
- how many pounds does our sun weigh?? :1(4 votes)
- how much does 10 atoms weigh(4 votes)
- How much does a human weigh in oz?(3 votes)
- depends on the human(2 votes)

## Video transcript

Identify the most
reasonable units to measure the weight
of the choices below. So we have an average
adult, a slice of bread, a kitchen table,
or a pack of gum. So I am an average
adult, and I know that I weigh about 160 pounds. So I know that pounds are
a pretty good measurement for about something
the weight of an adult. So I'll put adults in that
category right over there. Now we have a single
slice of bread. So even a full loaf of
bread doesn't weigh a lot. Maybe that gets close to a
pound, but a slice of bread is going to be
less than a pound. So I would do this in ounces. A kitchen table. Well, a kitchen table
kind of weighs the same-- it could, if it's a very
large kitchen table, could weigh the same
or more than an adult. So I would do this in pounds. And then a pack of gum. So once again, a pack
of gum is fairly light. If you've ever been
to the gym and held even a 1-pound or
2-pound weight, it weighs more
than a pack of gum. So a pack of gum is going
to be less than a pound, so ounces seem to
make sense here.