- Thread starter
- Banned
- #1
Welcome to our community
Be a part of something great, join today!
Instantaneous velocity
- Thread starter Poirot
- Start date
- Mar 10, 2012
- 835
Re: Instanaeous velocity
Can you elaborate on "the car is motionless at every instant"??
To define what it means to say that a car is going at the speed of 2mph would again require the use of limits. If $\lim_{h\to 0}\frac{x(t_0+h)-x(t_0)}{h}=2$ then the speed at $t=t_0$ is $2$, where $x(t)$ is the displacement of the car from any given reference at time $t$. But I guess you already knew that. I don't what more can I say.
Can you elaborate on "the car is motionless at every instant"??
- Thread starter
- Banned
- #3
- Mar 10, 2012
- 835
- Thread starter
- Banned
- #5
Re: Instanaeous velocity
In fact, the 'issue' generalises to differentiation of non-linear functions. Take f(x)=x^2.
when x=2, the derivative is 2. Now if one is asked to explain what a derivative tells you, then you would probably say along the lines 'the rate of change of y with x'. But what does the rate of change mean at a single point? I hope this helps you to understand.
In fact, the 'issue' generalises to differentiation of non-linear functions. Take f(x)=x^2.
when x=2, the derivative is 2. Now if one is asked to explain what a derivative tells you, then you would probably say along the lines 'the rate of change of y with x'. But what does the rate of change mean at a single point? I hope this helps you to understand.
- Mar 10, 2012
- 835
Re: Instanaeous velocity
If yes, then what is the average rate between $2$ and $2+h$ for h=1, 0.9, 0.8,...,0.1 ?
Does some pattern emerge? As $h$ gets smaller and smaller, you don't have average rate between two distinct points. The two points 'merge'. Thus the rate of change of y with x at x=2 is the avergae rate of change between 2 and 2.
Of course this is just an intuitive way of looking at it. The real thing is limits. But one should know that the concept of limits is just a formalization of our intuition, just as most of mathematics is.
Would you agree that the 'average rate of change' between $2$ and $4$ of the function $y=x^2$ is $(16-4)/2=6$?
If yes, then what is the average rate between $2$ and $2+h$ for h=1, 0.9, 0.8,...,0.1 ?
Does some pattern emerge? As $h$ gets smaller and smaller, you don't have average rate between two distinct points. The two points 'merge'. Thus the rate of change of y with x at x=2 is the avergae rate of change between 2 and 2.
Of course this is just an intuitive way of looking at it. The real thing is limits. But one should know that the concept of limits is just a formalization of our intuition, just as most of mathematics is.
if you are looking for an explanation of instantaneous velocity, then instantaneous velocity is the velocity at a specific moment. If a car is travelling along a road and had to stop for a red light and such, the motion of car against time will not be linear and therefore will not contain a constant gradient and if you wish to find the gradient of a specific point in a graph where the motion of car is against time, at a specific point then instantaneous velocity comes in handy.
Re: Instanaeous velocity
It means exactly what the definition says. The rate of change at a point is the limit of the average rate of change over intervals containing the point as the length of the intervals decrease to zero (with due allowances for end effects which I can't be bothered with here).
If you want to quibble about average rate of change over an interval the answer is just the same, it is defined to be the change in the function value divided by the corresponding change in x (the interval length).
There is no metaphysical mystery here, just a definition.
.
It means exactly what the definition says. The rate of change at a point is the limit of the average rate of change over intervals containing the point as the length of the intervals decrease to zero (with due allowances for end effects which I can't be bothered with here).
If you want to quibble about average rate of change over an interval the answer is just the same, it is defined to be the change in the function value divided by the corresponding change in x (the interval length).
There is no metaphysical mystery here, just a definition.
.
Last edited: