What is an example of direct proportionality?

In summary, direct proportionality refers to a relationship between two variables where one increases or decreases in the same proportion as the other. A commonly used formula for this is y = Ax, where A is a constant. However, it is important to note that A should not be a positive constant less than 1, otherwise the relationship between the variables would be inversely proportional.
  • #1
sotellme
75
0
directly proportional? can anyone give an example of it?


thanks alot!
 
Mathematics news on Phys.org
  • #2
y and x are directly proportional, A is a constant.

[tex] y = Ax [/tex]

[tex] \frac{y}{x} = A [/tex]
 
  • #3
Right. This is represented as [tex]y\propto x[/tex].
 
  • #4
thanks! :smile:
 
  • #5
Careful. Make sure A is not a positive constant < 1. Otherwise you will get that they are inversely proportional.
 
  • #6
cyby said:
Careful. Make sure A is not a positive constant < 1. Otherwise you will get that they are inversely proportional.


hi cyby! what you mean with that? do you mean that A must always be a positve number if not it will be inversely proportional? :cry:
 
  • #7
cyby said:
Careful. Make sure A is not a positive constant < 1. Otherwise you will get that they are inversely proportional.

No, that's not true. It's still a direct proportion. y and x are inversely proportional if y=A/x.
 
  • #8
Uh, you are right. Sorry, was thinking about something else completely.
 

1. What does "directly proportional" mean?

"Directly proportional" means that two quantities increase or decrease at the same rate. In other words, as one quantity increases, the other quantity increases by a constant factor.

2. How do you determine if two quantities are directly proportional?

To determine if two quantities are directly proportional, you can plot them on a graph and see if they form a straight line passing through the origin. Alternatively, you can divide one quantity by the other and see if the ratio remains constant.

3. What is the formula for direct proportionality?

The formula for direct proportionality is y = kx, where y is the dependent variable, x is the independent variable, and k is the constant of proportionality.

4. Is a direct proportionality always linear?

Yes, a direct proportionality is always linear because the graph of two directly proportional quantities will always form a straight line passing through the origin.

5. Can a direct proportionality exist if one quantity is negative?

Yes, a direct proportionality can exist if one quantity is negative. In this case, the graph will still form a straight line passing through the origin, but it will have a negative slope.

Similar threads

Replies
3
Views
1K
Replies
15
Views
2K
Replies
3
Views
826
  • Introductory Physics Homework Help
Replies
4
Views
527
  • Astronomy and Astrophysics
Replies
11
Views
1K
Replies
4
Views
2K
Replies
3
Views
1K
Replies
0
Views
524
  • Mechanical Engineering
Replies
7
Views
1K
Replies
14
Views
1K
Back
Top