Relation between acceleration and time

Click For Summary

Discussion Overview

The discussion revolves around the relationship between acceleration and time, particularly in the context of an engine's performance. Participants explore how varying acceleration can be represented graphically and the implications for torque and power in mechanical systems.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant questions the shape of the graph representing varying acceleration over time, specifically if it would be a straight line with a negative slope or another form.
  • Another participant argues that without additional information, it is impossible to determine the acceleration profile, comparing it to predicting a car's speed without context.
  • A participant clarifies that a horizontal line on a graph indicates constant acceleration, while a negative slope indicates decreasing acceleration, prompting a question about the specific nature of the acceleration change.
  • Some participants note that cars typically have maximum acceleration at the start, which then decreases, but this can vary based on specific conditions like parking or traffic.
  • A later post introduces a parabolic shape for the acceleration-time graph, suggesting a specific mathematical representation.
  • Participants discuss the relationship between torque, power, and acceleration, with one providing a formula that relates these variables, contingent on knowing torque, mass, and radius.
  • Another participant proposes a specific equation for acceleration that decreases over time, providing an example to illustrate the concept, while also questioning the constant used in the equation.
  • There is a request for clarification on the constant in the proposed equation and how it was derived, indicating ongoing exploration of the topic.

Areas of Agreement / Disagreement

Participants express differing views on the nature of acceleration changes and the appropriate mathematical representation. There is no consensus on a definitive model or equation, and the discussion remains unresolved regarding the specifics of the acceleration profile.

Contextual Notes

Limitations include the lack of specific data on acceleration changes, torque values at different times, and the assumptions made in the proposed equations. The discussion relies on hypothetical scenarios and does not resolve the mathematical steps involved in deriving constants.

Who May Find This Useful

This discussion may be of interest to those involved in automotive engineering, physics students exploring dynamics, or anyone interested in the mechanics of acceleration in vehicles.

Ketan Vadher
Messages
5
Reaction score
0
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?
 
Engineering news on Phys.org
This is impossible to tell without more information. It's like asking "here is a car, what will its speed be over time?"
 
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?
 
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.
 
insightful said:
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.
 
Thank you for such a response to my first question to Physics forum.
 
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.
 
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 ##
 
Ketan Vadher said:
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?)
 
  • #10
insightful said:
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.
 
  • #11
Ketan Vadher said:
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.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
1K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 17 ·
Replies
17
Views
1K
Replies
10
Views
1K
  • · Replies 18 ·
Replies
18
Views
4K
  • · Replies 167 ·
6
Replies
167
Views
9K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 8 ·
Replies
8
Views
7K