Relation between acceleration and time

[Ketan Vadher]

I have a problem. As I was finding the torque for an engine. I have. I get a question about the relation of acceleration and time.
How will be the graph of varying acceleration and time if acceleration decreases?
Will it be a straight line with negative slope or any other shape?

 

[mfb]

This is impossible to tell without more information. It's like asking "here is a car, what will its speed be over time?"

 

[RUber]

If you are plotting acceleration on the y-axis and time on the x axis, then a horizontal line would indicate constant acceleration. Negative slope indicates decreasing acceleration, and positive slope indicates increasing acceleration.
The question is, how is your acceleration changing? Do you have a formula for it?

 

[insightful]

Most cars (including drag racers) have maximum acceleration near t=0. Then acceleration declines rather quickly before curving to a more gentle downward slope. You'll need data and curve-fitting techniques to find the formula for your application.

 

[mfb]

Most cars (including drag racers) have maximum acceleration near t=0.

Not if they are parking somewhere (a=0), or moving in traffic jams or whatever. That's the point, we have no idea what happens so it is impossible to know the acceleration.

 

[Ketan Vadher]

Thank you for such a response to my first question to Physics forum.

 

[Ketan Vadher]

Hello
Today I get the graph of acceleration and time for my engine.
It will have a shape of paarabola x=-y^2 in first qudrent from Max acceleration to a=0.

Now I have a question regarding the reletion of power and acceleration & relation of torque and acceleration.
How to get relation for my engine. having max torque 18.6 N-m @2800 rpm.
how can I accelertion from power.

 

[RUber]

This web page spells it out pretty simply. http://theory.uwinnipeg.ca/physics/rot/node5.html
If you know torque, $\tau$, mass, m, and you know the radius of the thing you are rotating, $r$, you can relate torque to acceleration by:
$\tau = m r a$

 

[insightful]

Hello
Today I get the graph of acceleration and time for my engine.
It will have a shape of paarabola x=-y^2 in first qudrent from Max acceleration to a=0.

Now I have a question regarding the reletion of power and acceleration & relation of torque and acceleration.
How to get relation for my engine. having max torque 18.6 N-m @2800 rpm.
how can I accelertion from power.

I assume you mean to end up with an equation like:

a = a₀ - C*sqrt(t)

For example, if initial acceleration were 1 m/s² and acceleration drops to 0 after 20 seconds, you have:

a = 1 - 0.2236*sqrt(t)

Now, if you know the torque from the engine at a point in time, you can calculate the acceleration by calculating the force the wheels are applying to the vehicle, using F = ma. In practice, this is not possible because engine torque is not known at every point in time.

(Are we talking about a vehicle, like a motorbike?)

 

[Ketan Vadher]

I assume you mean to end up with an equation like:

a = a₀ - C*sqrt(t)

For example, if initial acceleration were 1 m/s² and acceleration drops to 0 after 20 seconds, you have:

a = 1 - 0.2236*sqrt(t)

Now, if you know the torque from the engine at a point in time, you can calculate the acceleration by calculating the force the wheels are applying to the vehicle, using F = ma. In practice, this is not possible because engine torque is not known at every point in time.

(Are we talking about a vehicle, like a motorbike?)

Thank you for response...

But what is the C here?
How did you get the value of C=02236 here?

I am making an ATV car.

 

[insightful]

But what is the C here?
How did you get the value of C=02236 here?

C is a constant in the equation. It is found by putting my assumption in the example I gave that a=0 at t =20 s:

0 = 1 - C*sqrt(20) and solve for C.