<p>Theoretically, the responsiveness of quantity demanded is different at different prices. Take the equation for the elasticity of demand:
<span class="math-container">$$\epsilon_{D}=\frac{\Delta{Q}}{\Delta{P}}\frac{P}{Q}$$</span>
The equation itself is non-constant as it depends on P and Q. Lets assume a linear demand curve with the simple form: <span class="math-container">$P(Q)=6-Q$</span>. If we take an equal change in price, say <span class="math-container">$\Delta{P}=1$</span>, and since the demand curve is linear in this case, we see it has a slope = <span class="math-container">$-1$</span> and thus the <span class="math-container">$\Delta{Q}=1$</span>. If we have two situations where <span class="math-container">$P=5$</span> and <span class="math-container">$P=4$</span>, then, to keep in accordance with our slope, lets say <span class="math-container">$Q=1$</span> and <span class="math-container">$Q=2$</span>, respectively.
The two elasticities of demand for these two prices would be <span class="math-container">$\epsilon_{D}=5$</span> and <span class="math-container">$\epsilon_{D}=2$</span> for the higher and lower price respectively.</p>

<p>In short, the elasticity of demand is a function of the responsiveness of quantity demanded to changes in prices that <em>depends</em> on the current price/quantity combination.
At a higher point up the demand curve, the elasticity is higher, or demand more elastic, than at lower points.</p>

CC BY-SA 4.0
2019-07-04T01:14:54.690Z
2019-07-04T01:14:54.690Z
Brennan
<p>There are different zones of elasticity on a graph, but if we are to imagine a negatively sloped, straight line on a price v quantity graph, we find that elasticity differs based on where we look on the graph. Why is this the case, rather then elasticity being constant?</p>

CC BY-SA 4.0
2019-07-04T09:49:47.073Z
Welcome to the site.  You may find answers to [this question](https://economics.stackexchange.com/questions/14162/why-is-elasticity-not-defined-simply-as-the-slope-of-the-graph/14169#14169) helpful.
Adam Bailey
<microeconomics><elasticity>
Why is elasticity not constant on a straight line graph?
fyiitsme
# Why is elasticity not constant on a straight line graph?

(Asked by: username_0 on 2019-07-04)

There are different zones of elasticity on a graph, but if we are to imagine a negatively sloped, straight line on a price v quantity graph, we find that elasticity differs based on where we look on the graph. Why is this the case, rather then elasticity being constant?

**Tags:** microeconomics, elasticity

> **Comments:**
> **username_1**: Welcome to the site.  You may find answers to [this question](https://economics.stackexchange.com/questions/14162/why-is-elasticity-not-defined-simply-as-the-slope-of-the-graph/14169#14169) helpful.  

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## 1 answers

### Answer by username_2 on 2019-07-04. Score: 2

Theoretically, the responsiveness of quantity demanded is different at different prices. Take the equation for the elasticity of demand:
$$\epsilon\_{D}=\frac{\Delta{Q}}{\Delta{P}}\frac{P}{Q}$$
The equation itself is non-constant as it depends on P and Q. Lets assume a linear demand curve with the simple form: $P(Q)=6-Q$. If we take an equal change in price, say $\Delta{P}=1$, and since the demand curve is linear in this case, we see it has a slope = $-1$ and thus the $\Delta{Q}=1$. If we have two situations where $P=5$ and $P=4$, then, to keep in accordance with our slope, lets say $Q=1$ and $Q=2$, respectively.
The two elasticities of demand for these two prices would be $\epsilon\_{D}=5$ and $\epsilon\_{D}=2$ for the higher and lower price respectively.

In short, the elasticity of demand is a function of the responsiveness of quantity demanded to changes in prices that *depends* on the current price/quantity combination.
At a higher point up the demand curve, the elasticity is higher, or demand more elastic, than at lower points.


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