S1xN1=S2xN2

Big_tee19 · 2011-04-03 06:54:34

Help its been awhile since Ive done these and im getting miixed up looking thru my old notes

this is for speed caluations

I have... driver speed x number of teeth = driven speed x number of teeth

or s1/s2=n2/n1

or input speed = # teeth in driven
_________ _____________
output speed #teeth in driver

now i have an gear with 500 rpm input speed driver has 5 teeth driven has 60 teeth

so now i put down 500/s2=60/5

so i,m getting mixed up with cross multiplying

how do know which numerator and denominator to switch??????

does the s1 always stay the denominator ?????? can any one give me some tips???

bobbym · 2011-04-03 06:59:40

Hi Big_tee19;

Welcome to the forum.

Cross multiply.

Divide both sides by 60 to get output speed by itself.

The 60 cancels on the left.

Figure the right hand side with a calculator.

Here it is all done for you so you just plug in 3 to get the 4th on the left.

Big_tee19 · 2011-04-03 07:21:03

thank you thats what i have but what i did
S1/S2 = N2/N1 = 500/S2= 60/5
then i cross multiplied i switched the 60 and the 5
but how do i know which fraction to switch?
my question is basicly.... if i was to switch the 500/S2
i would get a different awnswer or if the N2 was the missing number
i cant remember the rule on which fraction to switch when i cross multiply

bobbym · 2011-04-03 07:24:24

Hi;

First check what I have done in the post above yours. I have made it easy for you to solve for the fourth quantity when you know 3. Please look at it and see if it helps you.

Big_tee19 · 2011-04-03 08:04:02

thx for your help im just tryimng to remember a rule if there is one?????

so i,ll try to remember it by if i cover the missing numerator that denominator goes up
if i cover the missing denominator the other fraction switches???

this should work in any x1/x2= y2/y1 equation shouldn't it ?????

bobbym · 2011-04-03 08:21:28

Hi Big_tee19;

When you cross multiply this is what happens;

The top of the left multiplies the bottom of the right.

The bottom of the left multiplies the top of the right.

Then they are just set equal to each other.

It is top times opposite bottom = bottom times opposite top. From left to right. Notice there is no more fraction. That is the mechanism for these type.

The rules you are trying to use should be phrased like this:

If you want the numerator on the left put the denominator to the right on top.

If you want the denominator on the left, then turn both fractions upside down and put the denominator on the left to the top on the right.

Big_tee19 · 2011-04-03 09:11:01

lol so if you want the missing denomiator on the right???????
my way still works??????

Big_tee19 · 2011-04-03 09:14:22

so if i see A x D = B x C and i need to know A??? how do i write that?

bobbym · 2011-04-03 12:17:21

Hi;

lol so if you want the missing denomiator on the right???????
my way still works??????

Then just switch the right fraction to the left side and the left fraction to the right and use your rules.

so if i see A x D = B x C and i need to know A??? how do i write that?

Just divide both sides by D. the D on the left will disappear. You will end up with.

I have already done every possible problem you will encounter in post #2.

Math Is Fun Forum

#1 2011-04-03 06:54:34

S1xN1=S2xN2

#2 2011-04-03 06:59:40

Re: S1xN1=S2xN2

#3 2011-04-03 07:21:03

Re: S1xN1=S2xN2

#4 2011-04-03 07:24:24

Re: S1xN1=S2xN2

#5 2011-04-03 08:04:02

Re: S1xN1=S2xN2

#6 2011-04-03 08:21:28

Re: S1xN1=S2xN2

#7 2011-04-03 09:11:01

Re: S1xN1=S2xN2

#8 2011-04-03 09:14:22

Re: S1xN1=S2xN2

#9 2011-04-03 12:17:21

Re: S1xN1=S2xN2

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