I think we have all heard someone say that they'd like their weight better if they were on the Moon. Why? Well, because when you're on the Moon there is less gravitational force than there is on Earth. According to Google, the gravitational force on the Moon is 1.62 meters per second squared, while the gravitational force on Earth is 9.807 meters per second squared. That is slightly six times stronger than the Moon. Fun fact! You really don't want to weigh yourself on Jupiter where the force of gravity is 24.79 meters per second squared.
As we've learned multiple times throughout this chapter, we do things slightly different in the United States than the majority of the world. I'm sure most of you were raised using units like pounds and ounces to weigh yourself. In the United States, when a baby is born, they declare that it weighs something like eight pounds, seven ounces and is 21 inches long. However, other countries will say a baby weighs 3.83 kg and is 53.3 cm long.
What really is the difference between English measurements for weight and the Metric measurement for weight? Well, for starters, a gram is not a measurement of weight; it is a measurement for Mass! The weight of an object is the measure of gravitational pull on it, thus a person’s weight can vary based on their distance from the equator. Whereas mass is a constant measure of the physical size of an object regardless of location. Meaning, that 50 kg on the Moon is the same as 50 kg on Earth.
| English Units | Metric Units | Conversions |
|---|---|---|
| 16 ounces (oz) = 1 pound (lb) | 1 kilogram (kg) = 1,000 grams (g) | 1 kg ≈ 2.2 lbs |
| 2,000 lbs = 1 ton (T) | 1,000 kg = 1 Metric Ton (t) | 1 oz ≈ 28 g |
In Men's Bodybuilding there are typically multiple weight classes. Those that fall into the Middleweight class have to weigh between 157 lbs to 176 lbs. If Rico weighs 81 kg, will he make weight for the Middleweight class? What is his weight in grams?
First, convert Rico's weight into pounds. Using the conversion factor 1 kg ≈ 2.2 lbs:
$$ \frac{81\ \text{kg}}{1} * \frac{2.2\ \text{lbs}}{1\ \text{kg}} = 178.2\ \text{lbs} $$
178.2 lbs is outside the range of 157–176 lbs, so Rico cannot compete in the Middleweight class.
Next, convert his weight to grams. Moving from kilo to grams means multiplying by $10^3$:
$$ 81\ \text{kg} * 10^3 = 81,000\ \text{g} $$
While on vacation in Cabo, Mexico, you get sick. You pick up some medicine from the drug store and the package says to take 15 mg per kg of body weight. The packaging says one dose of medicine is 200 mg. If you weigh 178 lbs, how many doses do you need?
Start by converting your weight into kg using the same factor as before:
$$ \frac{178\ \text{lbs}}{1} * \frac{1\ \text{kg}}{2.2\ \text{lbs}} = 80.9\ \text{kg} $$
Next, multiply by 15 mg per kg:
$$ 80.9\ \text{kg} * 15\ \text{mg/kg} = 1213.5\ \text{mg} $$
Divide by 200 mg per dose:
$$ \frac{1213.5\ \text{mg}}{200\ \text{mg}} = 6.07\ \text{doses} $$
You will need 6 doses (cannot take a fraction of a dose).
I think most people can agree that they like to be thrifty shoppers. But sometimes, when being thrifty, we forget to check boxes for instructions. While shopping at an outlet grocery store, I found a large self-rising crust supreme pizza for \$0.50. I get home and see the directions say to bake for 20 minutes at $107^\circ$C. My oven only has Fahrenheit, so I need to convert.
| Fahrenheit | Celsius | |
|---|---|---|
| F = (9/5)C + 32 | C = (5/9)(F - 32) |
In the English system we use Fahrenheit (freezing 32°F, boiling 212°F, body 98.6°F). In the Metric system, they measure temperature in Celsius. Freezing is 0°C, boiling is 100°C, body temperature is 37°C.
Looking back at the pizza issue, what temperature would I need to set my oven to if the box said $107^\circ$C?
$$ F = \frac{9}{5}(107) + 32 $$ $$ F = 192.6 + 32 $$ $$ F \approx 225^\circ\text{F} $$
Meaning I would set the oven to 225°F.
You've invited your friend from Australia. The weather will be around 97°F. What temperature is that in Celsius?
$$ C = \frac{5}{9}(97 - 32) $$ $$ C = \frac{5}{9}(65) $$ $$ C \approx 36^\circ \text{C} $$
Your friend will be comfortable as that is close to normal body temperature of 37°C.