A little confused.......

[Macroscopic]

How do you solve problems like f=ma? For each variable, you put in a different number, but they are described in different units, like pounds, or pounds per square inch. How does it work?

[5614]

well if you have:

f=ma

 

f = force measure in newtons

m = mass measure in grams or kilograms

a = acceleration measured in unit of speed per unit of time squared e.g. meters per second squared... like you dont square the time, just it'd be written like m/s^2

 

pounds is like kilograms, its a measure of mass

pounds per sqaure inch is, i think, a measure of force.

 

you are running into the problem of the world not having standard units.

 

if you are learning for a test, the exam board will normally ask all questions using the same set of units, from my experience they do anyway, when it comes to the 'real world' its up to you to measure it in the same way, or get a unit converter!

[Macroscopic]

{Quote}if you are learning for a test, the exam board will normally ask all questions using the same set of units, from my experience they do anyway, when it comes to the 'real world' its up to you to measure it in the same way, or get a unit converter! {/Quote}I didn't mean different units as in grams and kilograms, which are interchangeable. I meant different types of measurement completely, like newtons and pounds. F=ma. Replace it with xnewtons=5pounds*2km per minute per minute. So you get 10 newtons right? But if you change 5pounds to 80 ounces. They are equal,right? Let's try it again.

F=80ounces*2km per minute. Now f equals 160 newtons. It shouldn't be any different because 80ounces=5pounds. That's the problem.

[5614]

1 ounce = 0.0625 pounds

or

16 ounces = 1 pound

 

when you use f=ma there will be a set unit for use in that equation, you cant use ounces or pounds, because as you clearly demonstrated it will produce different answers.

 

so you need to know the set unit for it.

 

with f=ma i know that f=newtons, m=KG, a=m/s^2

 

for the imperial measurement system i do not know which to use.

[Macroscopic]

{Quote} you dont square the time, just it'd be written like m/s^2 {/Quote} You say don't square the time then say s^2. Did you mean (m/s)^2

[5614]

m = meters

/ = divided by

s = seconds

^2 = squared

 

you dont actually square the time unit (seconds), that's how it is written though.

[Mart]

m stands for distance measured in units of space (metres, inches, etc)

s stands for time measured in units of time (seconds, years, etc)

 

m/s^2 means how speed changes with time. m/s = speed and m/s^2 = change of speed with respect to time on a clock

[5614]

You say don't square the time then say s^2. Did you mean (m/s)^2

 

you use [ and ] for the quote tags!

 

i dont know how it works, i've never thought of it, acceleration is measured using the formula:

 

a = (v-u)/t

 

where

 

a = acceleration

v = end speed

u = original speed

(v-u) = change in velocity

t = time

 

but its written as m/s^2... as i said, i dunno why... let's see what someone else has to say on the matter.

[Macroscopic]

Ok, thanks, that cleared it up.

[jordan]

I was told recently to think of a in the more accurate terms of N/kg rather than m/s².

 

F=ma. Replace it with xnewtons=5pounds*2km per minute per minute. So you get 10 newtons right? But if you change 5pounds to 80 ounces. They are equal,right? Let's try it again.

F=80ounces*2km per minute. Now f equals 160 newtons. It shouldn't be any different because 80ounces=5pounds. That's the problem.

As for that part, the numbers are all right, but you're not measuring in the right units. The answer to the first one isnt' 10N, it's 10(lb*kg/min²). The second one is being measured in onces*kg/min². Neither of those are equivalent to a Newton. You need to convert everything to consistant units. It doesn't matter what you want to use, as long as it's the same for the first and the second. Once the units all line up, the magnitudes will follow.