# Unit Conversion: SI to British Units with Real-Life Consequences

• Moninder
In summary, the conversation discusses the importance of unit conversion and provides a real-life example of its consequences. The two groups of scientists and engineers use different units, and conversions are necessary for communication. The unit of force in the SI system is Newton (N) and in the British system is pound (lb). The conversation also provides tips for successful unit conversion, including the concept of units canceling like variables and multiplying by 1. The conversation also includes a step-by-step process for converting 15N to pounds using the conversions 1 slug=14.59kg and 1 ft=0.3048m, resulting in a final answer of 1.028lb.
Moninder

## Homework Statement

This is the question
Still think that unit conversion isn't important?
Here is a widely publicized, true story about how failing to convert units resulted in a huge loss. In 1998, the Mars Climate Orbiter probe crashed into the surface of Mars, instead of entering orbit. The resulting inquiry revealed that NASA navigators had been making minor course corrections in SI units, whereas the software written by the probe's makers implicitly used British units. In the United States, most scientists use SI units, whereas most engineers use the British, or Imperial, system of units. (Interestingly, British units are not used in Britain.) For these two groups to be able to communicate to one another, unit conversions are necessary.

The unit of force in the SI system is the Newton (N), which is defined in terms of basic SI units as 1N=1kg*m/s^2. The unit of force in the British system is the pound (lb), which is defined in terms of the slug (British unit of mass), foot (ft), and second (s) as 1lb=1 slug ft/s^2.
Part B
Find the value of 15.0 {N} in pounds. Use the conversions 1 slug=14.59kg and 1 ft}=0.3048m}.
I figured out 1.028 slugs=kg. but that's about it

It's impossible to resolve a difficulty if you don't mention what your difficulty is.

Two things to know for unit conversion though:

1). Units cancel just like variables of an algebraic expression. For example if I multiplied x/y and y together the lone y and the y on bottom of the fraction would cancel to 1 and I would be left with 1x or simply x.

2). You can multiply anything by 1 without changing it. So if I said x=y I could then multiply anything by x/y without changing its value because x/y would simply = 1. Notice because x = y it doesn't matter which is on top. I can multiply by x/y or y/x because both fractions are simply 1.

These are the ideas behind any unit conversion you do. As I said above, if you show an attempted answer, then people can help you with a specific difficulty you're having.

I eliminated the kg and change it into slugs, so now i have 1.028*.3048ft/s^2. I don't know what to do with the s^2 now? I change the equation from 15N=15kg* m/s^2. I don't know what to do with the ft

Hmm, are you sure you converted it into slugs? You're on the right track, but in your answer you give the units ft/s^2 but I don't see slugs?

Q1: What are the desired units for your final answer? You're going from kg*m / s^2 to _____ ?

Q2: Can you write a fraction in the form (something) / (something) that equals 1 from the information given in the problem?

Yes, I got the slugs correct I know for a fact, I need to find lb only.
1lb=1 slug ft/s^2

I guess I'm trying to see the process you used. Sometimes it's possible to use an intuitive method and happen upon the right answer. That's great, but if you're not sure why it worked, or not sure how to use it if given a different problem then the exercise loses its purpose even if you did get the right answer.

I was wanting you to think of it in terms of fractions and multiplying them, but if you're doing it a different way that's fine.

As for lb, it tells you pounds is slug*ft / s^2 So as long as your units are that, you're done.

## 1. How do I convert from one unit to another in the SI system?

To convert from one unit to another in the SI system, you can use conversion factors. These factors are numerical values that represent the relationship between two units. For example, to convert from meters (m) to kilometers (km), you can use the conversion factor 1 km = 1000 m. Multiply the value in meters by this conversion factor to get the equivalent value in kilometers.

## 2. Are there any shortcuts for converting between SI units?

Yes, there are some shortcuts you can use for converting between SI units. For example, if you are converting between units that are in the same category (e.g. length, mass, time), you can simply move the decimal point to the left or right depending on which unit is larger or smaller. For example, to convert from centimeters (cm) to meters (m), move the decimal point 2 places to the left. So 100 cm = 1 m.

## 3. How do I convert units with prefixes in the SI system?

When converting units with prefixes in the SI system, you can use the same method as before, but you also need to take into account the prefix. For example, to convert from milliliters (mL) to liters (L), you need to multiply the value in mL by the conversion factor 1 L = 1000 mL. This is because the prefix "milli" means 1/1000. So 100 mL = 0.1 L.

## 4. Can I use a calculator for SI unit conversions?

Yes, you can use a calculator for SI unit conversions. In fact, it is recommended to use one to avoid any errors in your calculations. Just make sure to enter the conversion factor correctly and double check your work to make sure you are using the correct units.

## 5. How do I check if my conversion is correct?

To check if your conversion is correct, you can use the dimensional analysis method. This involves checking the units on both sides of the equation to make sure they cancel out and you are left with the unit you are trying to convert to. Additionally, you can double check your calculation by using a different conversion method or checking with an online conversion tool.

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