!Math Formulas for Automotive Mechanics!

Using formulas in the automotive industry

1. Formulas

2. What is it?
Like formula 1 racing?
Not quite…

4. Define
Formula is a math sentence
Can predict results based on various
inputs
The formula won’t change but the
inputs can
Example:
For every can of pop I drink, I burp 8
times
Total burps = 8c when c is the number
of cans of pop
How much will I burp if I drink 3 cans?
10 cans?

5. PEMDAS
A formula may have more than one operation
Which do you do first?
Use the sentence Please Excuse My Dear Aunt
Sally to remember!
Parentheses Exponents Multiplication Division
Addition Subtraction
If there is both multiplication and division, go from
left to right
Same with addition and subtraction
Should really look like PE[MD][AS]

6. Example
y = 2 x (7 –2) + 3
Parentheses first
7-2 = 5
y = 2 x 5 + 3
No exponents so multiplication next
2 x 5 = 10
y = 10 + 3
No division, so addition next
10 + 3 = 13
y = 13

7. Difference?
Wrong way: Left to right
y = 2 + 3 x 6
2 + 3 = 5 x 6 = 30
Right way: PE[MD][AS]
y = 2 + 3 x 6
3 x 6 =18
y = 2 + 18
y = 20

8. Common Ones
Engine Displacement
Displacement = Bore x Bore x Stroke x 0.7854 x
Number of Cylinders
Horsepower
Horsepower = (Torque x RPM) / 5,252
Fuel Mileage
Fuel Mileage = miles driven ÷gallons of gas used
Torque
Torque = force x length

9. Boiled Down
Once you know the
formula to use, figure out
what inputs you know and
what you need to find out
Plug them in
Solve!

10. But wait…
What if I don’t know all the pieces of info on
one side of the formula?
Example:
Fuel Mileage = miles driven ÷gallons of gas used
I know the vehicle gets 22 miles/gal and I have 9
gallons in the tank, how far can I drive?
22 miles/gal = miles driven ÷9 gallons
Now what?

11. But wait…
22 miles/gal = miles driven ÷9 gallons
Multiply both sides by 9 to figure out miles
driven
22 x 9 = 198
So I can drive 198 miles with my 9 gallons of
gas
Multiplication is the inverse of division
Addition is the inverse of subtraction
Must do the inverse any time you go across
the equals sign

12. Hold On
Haven’t we been doing this all along?