Reaction time measurement

[Fu-Kwun Hwang]

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There are 17 translations, select to view translated versionEnglish(by klmonson: 77)Türkçe - Turkish(by turhan: 77)Español - Spanish(by jufevaro: 78)中文 - Chinese traditional(by Fu-Kwun Hwang: 79)ქართული - Georgian(by temchi: 150)English(by garethpillay: 77)Ελληνικά - Greek(by charmader: 77)ภาษาไทย - Thai(by jaja_05: 77)Slovenčina - Slovak(by jozefhanc: 148)Suomi - Finnish(by darkhero: 77)Español - Spanish(by gandalf: 19)English(by NAMANSAR: 25)Português - Portuguese(by Borges: 27)中文 - Chinese simplified(by Omega ou: 19)ภาษาไทย - Thai(by chang59: 20)Deutsch - German(by friedhelmmaas: 8)Deutsch - German(by ksarnow: 55)
Higher number at the end means more translation been done.

or

Reaction time : the lapse of time between stimulation and the beginning of response.

   Would you like to measure your reation time?
   Would you like to estimate how fast you can drive safely on the highway?


   You are driving on the high way and listening to the music you like most.

   Suddently, you see the brake light of the car in front of you just turned on.

   You will try to hit the brake and slow down your car.

   But, there is a small time delay before you really do that--- your reaction time.

   During that period of time, your car is still moving at the same HIGH speed!

   If you do not want something VERY BAD happened,

   What is minimum diatance between front of your car and the rear of the car before yours?

   If both cars need the same distance to fully stopped, the miniuum distance = ( the velocity of your car )* ( your reaction time )

New version of this simulation: Reaction time measurement

• Click Start to start the animation. Click Brake to stop the car.
• The time delay between the red light is turned on and you click the brake button will be shown in the textfield. (plus the time needed to stop the car after the brake is started. The corresponds distances which the car moved are also shown on the graph)
• Paramenters you can change(Hit ENTER key after you change value in the text field)
• Initial Velocity of the car : initial value is 72 km/h = 20 m/s
     You can select the unit for the velocity ( km/h, mile/h or m/s)
• Friction coefficient of tires on the road : initial value is 0.8



Typical value of tires	static coefficient	kinetic coefficient
auto tires on dry concrete	1.0	0.7-0.8
auto tires on wet concrete	0.7	0.5
auto tires on icyconcrete	0.3	0.02

• The Y-coordinate the the small dots are proportional to the velocity of the car
    Notice that it is not a straight line after the brake turned on! Because ...
• The mouseXV textfield shows X-coordinate and velocity of the car at the mouse position.
    If you drag the mouse, it will change to values of the relative distance and the relative velocity.
    (relative to the point where you started to drag the mouse)
• Press Reset button to restart the testing.
• Close the window to Quit.

Let's Assume: you are driving a car with speed v, and your reaction time is T_react.
When you find out something happened, you need time T_react to react (including time to hit the brake and time for the brake system to work).
Before the brake really start, the car already move another distanace D_react=v*T;
Assume the reaction is 0.8s (it is 0.6-1.0 for ordinary person. The reaction time will be longer if someone has been drinking or who is sick or tired).
For a car moving with speed 72 km/hr (which is equal to 20 m/s), it means that the car move another distance D_reaction=20*0.8=16m before the brake is activated. And it will take more time to stop the car (from v to 0).

Now. I am going to show you how to calculate the distance required for the car to be fully stopped.
The friction force between tries and the road is the only external force to slow down the car.
All the energy of the car goes to tires during the process of stopping the car (so the temperature of tires goes up).
Auusume the friction coefficient is μ, then the friction force fr=-μ*N =-μ*m*g where m is the mass of the car and g is the gravity. (μ is between 1-1.2 for ordinary tire and normal road condition. If it is raining, the friction coefficient can be reduced to less than 0.6, and it could be reduced to 0.2-0.4 for ice road condition).

From Newton's law F=m*a = -μ*m*g so a=-μ*g is the de-acceleration.
So the time for the car to stop T_brake=v/|a| = v/(g* μ).
During the above time interval, the speed reduced from v to zero linearly.
 the average speed = (0+v)/2 =v/2
So, the braking distance D_brake=average speed * T_brake= (v/2) * v/(g* μ)=v²/(2*g* μ)

What is the meaning of the above equation?
It tell us that the stopping distance is proportional to square of the driving speed.
If the speed is changed from 100 km/hr to 120 km/hr, the distance to fully stop the car change from d₁₀₀ to (144/100)*d₅₀=1.44 *d₁₀₀.

For the above case, v=72km/hr (45 mile/h)=20m/s. (g=9.8 m/s² and I wil use g=10 m/s² to simply the estimation, μ=1 is used)
D_brake=v²/(2*g* μ)= 20²/(2*10*1)=20 m

The driver need T_react to react and the car need T_brake to be fully stopped, which imply the total distance traveled is equal to D_react + D_brake = v*T_react + v²/(2*g*u).

For car at v=108 km/hr (67 mile/h) = 30 m/s :
 D_react= 30*0.8=24 m
 D_brake= 30*30/ (2*10*1)=45m
So, the car need 24+45=69m to fully stopped.
This is a very long distance (assume the length of the car is 3m, it is a distance of 23 cars in a line).

If several cars with the same speed are in line in high way, the minimum distance between cars is D_react. Because all the car need the same distance to fully. (recommend: multiple D_react by 1.5 as safty factor).

However, if you are driving on a road, and someone jump into the road from the sideway.
The car need D_stop=D_react+D_brake to fully stopped.
It is the same if a car accident happened in front of you.
All the cars within D_stop from the accident will bump into each other.

Please estimate your own reaction time and calculate D_react+D_brake for the maximum speed you normally drive in the high way. May be you will drive slower after you have calculated the value.

The police might not be there to give you a ticket when you drive too fast.
Nature law require D_react+D_brake=v*Treact+v²/(2*g*u) for a car to fully stopped.
You will alway receive ticket if you violate the NATURE LAW.
(You might be lucky if you were sent to hospital instead of ...).

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Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
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There are 17 translations, select to view translated versionEnglish(by klmonson: 77)Türkçe - Turkish(by turhan: 77)Español - Spanish(by jufevaro: 78)中文 - Chinese traditional(by Fu-Kwun Hwang: 79)ქართული - Georgian(by temchi: 150)English(by garethpillay: 77)Ελληνικά - Greek(by charmader: 77)ภาษาไทย - Thai(by jaja_05: 77)Slovenčina - Slovak(by jozefhanc: 148)Suomi - Finnish(by darkhero: 77)Español - Spanish(by gandalf: 19)English(by NAMANSAR: 25)Português - Portuguese(by Borges: 27)中文 - Chinese simplified(by Omega ou: 19)ภาษาไทย - Thai(by chang59: 20)Deutsch - German(by friedhelmmaas: 8)Deutsch - German(by ksarnow: 55)
Higher number at the end means more translation been done.

or

Dr. Hwang,

I appreciate your reaction time testing device. Is there any data about how the normal population reacts with your device? To measure reaction time, in seconds, do you divide by 20? Is the 20 meters per second?

Thanks for your help.

Steve sbw@dscience.com

[Fu-Kwun Hwang]

The first textfield (under label V=) is the velocity of the car. It is not the reaction time.
The reaction time is shown in the textfield under the label : [b:039696da07]Delay +Brake[/b:039696da07]
 where "Delay" is the reaction time and "Brake" is the time for the car to fully stopped.

Dr Hwang

Enjoy your site and use it all the time with my Physics classes.

I think your calculation of braking distance is wrong on the Reaction Time Measurement applet.

It always displays as 25.5 m regardless of speed.

It should increase as the square of speed. Can you fix this?

Paul

[Fu-Kwun Hwang]

I think you forgot to hit [b:b664fce8e0]ENTER[/b:b664fce8e0] after you have changed the number in the textFields.

Please try it again and it should work fine.
The following table will help you to calculate it!
You can enter reaction time,driving speed,friction coeffcient and select the speed unit.

reaction time	s
driving speed	km/hmile/hm/s
Dreact
friction coeffcient
Dbrake
Dstop

Dutch version web page

http://www.youtube.com/watch?v=xu3vpV_kBlU

http://www.youtube.com/watch?v=xI2461dDnwc

Hi Hawg, I think this is the coolest site and I shall tell all my friends about this site!

[mugluck]

this was the best thing i have ever done in my life, i am telling my kids to do it every day till they r 20.

mugluck signing off, *ZOLTAN*

[Fu-Kwun Hwang]

Someone send me video which shown car accident happened inside a tunnel in Russia.

[Overactive Imagination]

Hey I have a question
(I'm doing a school project on stopping dist. and whatnot)

Which formulaes are implemented in that program?
Thanks

- Luke

[Fu-Kwun Hwang]

The friction force = u * m*g = -m*a (u is the friction coefficient )
So a = -g*u
Then you can calculate the stopping distance d= v*v/(2*a)= v*v/(2*g*u)

Due to the reaction time dt , the actua stopping distance will be d+ v*dt;

[Overactive Imagination]

In the first forumula i'm assuming m stands for mass. What did you use as the mass?

Sorry if this is a stupid question

- Luke

[Fu-Kwun Hwang]

The mass is the mass for the car.
As you can see in this case, the result has nothing to do with mass.

[sanjeevgogna]

Hi i have downloaded JRE, but when i try to get the source files by clicking "Get Applet File" i get to see "no priveledge", please help and advice, warm regards: sanjeev

[Fu-Kwun Hwang]

Due to hacker attack. We added some checking for browser. May be your browser did not support those functions we were checking. I just turn off the checking. Please try it again!

[Felsager]

Dear professor Hwang

I downloaded the applet as a zip-file, unpacked it and tried to use it offline, but it does not show the full story: The images are not shown and there are no buttons, so I cannot run the simulation offline. Have you some suggestion as to what might be wrong?

Yours sincerely

Bjørn Felsager

Lecture in physics?/p>

[Felsager]

Dear Professor Hwang,
I found out what was wrong. I was the problem or rather my name. It contains an unusual Danish character (ø) and this means that when I save your applet to a folder in my documents all path-names will contain this unusual character. But the applet cannot handle unusual characters in path names. I moved the applet to the root-directory (C:\) and all problems disappeared. I post the answer because other users may experience similar problems.
Yours sincerely
Bjørn Felsager
Lecturer in physics
Haslev Gymnasium & HF
Denmark

[Fu-Kwun Hwang]

Thank you for your posting. Yes. Some one else might have the same problem.
If the directory name contain space or some other special characters which might be allowed in Microsoft Windows system, would not work in java.

[i h8 chinks 2]

ite m8  i really like your website

[i h8 chinks 2]

Dear Professor Hwang,
I found out what was wrong. I was the problem or rather my name. It contains an unusual Danish character (ø) and this means that when I save your applet to a folder in my documents all path-names will contain this unusual character. But the applet cannot handle unusual characters in path names. I moved the applet to the root-directory (C:\) and all problems disappeared. I post the answer because other users may experience similar problems.
Yours sincerely
Bjørn Felsager
Lecturer in physics
Haslev Gymnasium & HF
Denmark

[roma100]

Hi,

I would like to get the source code of this reaction time measurement applet. The applet is really great.

Thanks

[Fu-Kwun Hwang]

This applet was created 10 years ago with JDK1.0.2.
There is an EJS version of the same applet. You will be able to find the EJS source from that page.

[roma100]

Dear Professor Hwang,

Do you also have the java source code of this reaction time measurement applet? I have problems with the EJS one...

Thanks

[g3mini]

Hi Professor

I am just a lay person who has a questions about driving and physics. My boyfriend and I disagree about what would happen in the below scenario:

You are driving on a major highway in a Toyota Corolla, it's pouring rain, there is a transport truck in front of you (he is hauling a trailer), you are both doing 110 km/hr and you are about 1 1/2 car lengths behind him (somewhat tailgating). The truck driver slams on his brakes suddenly - given normal reaction time (or even super-human reaction time), would you be able to stop in time to not hit him?
I understand that transports have a greater braking distance, but once he's touched his brakes, at the rate you are going, and your reaction time, would you not hit him being so close? At what distance would you have to be in order to not hit him?
Would you even have time to swerve around and avoid him?

I do not think that you would be able to have enough time to react and avoid hitting the back of the truck, however he thinks you do.

Any help would be greatly appreciated!
Kind Regards
Tracy

[Fu-Kwun Hwang]

The speed is 110km/hr, it is about 30m/s (=108km/hr).
The distance between cars is about 1 1/2 car lengths (assume to be 5m).

The best reaction time for person driving car is 0.6 s (up to 1s for ordinary person).
So the minimum distance required will be 0.6s* 30 m/s=18m (30m max.)

The reaction time is the time between you saw what happened, and the time you really react to it.
During that time interval, your car will move with the same velocity.
Yes. the car in front of you also moving at the same time, However, the car in front of you starts to slowing down while you are moving at the same speed.
Without consider the thermal effect and assume the brake work perfectly, the stopping distance for both car will be the same.
Due to the thermal effect, larger car will have longer stopping distance (ABS braking system can help to reduce the braking distance to theoretical value).
If you think the difference between the braking distances are more than 18-5=13m (25m max.)
You can try to risk you life. But I would not bet on it.

I would suggest:
Count one second and see what is the distance you car has move.
It is the same minimum distance you should keep between your car and the car in front of you.

Please try to visit Reaction time and car accident to test it with a simulation.

If you think your reaction time is better than 1 second. You can reduce the distance a little bit. (I would not suggest you did that).
But if something happened, you can try to argue the physics with God if you meet with him.

[g3mini]

Thank you for your response.
So realistically, there is no chance that you could get your car stopped in time without hitting the back of the truck, right?

[Fu-Kwun Hwang]

Yes. I would say more than 95% that your car will hit the truck in front of you. Unless the braking system of the truck is not function normally(less than 5%).

[g3mini]

Thank you for your help!

[Fu-Kwun Hwang]

For your information:

For 0.8 s reaction time, driving at 30 m/s (108km/hr),  the car will move 30*0.8=24m before you hit the brake.
And the car will fully stopped after moving 30*30/(2*9.8*1)m,  about 45m.
(Police will you the length of the tire trace on the road to estimate the speed of the car).

[John256]

Dr Hwang, would the friction coefficients you posted (rubber on dry pavement = 0.8, etc) equate to the stopping distance if you braked hard enough to lock the wheels and came to a skidding stop?  Would braking distance without locking the wheels be significantly better? 

Thank you!

[Fu-Kwun Hwang]

The table at the top message,shows both static coefficient and kinetic coefficient (One for static friction and another one for sliding friction).
The static coefficient is always slightly larger than the kinetic coefficient (if you lock the wheels).
If you brake too hard and lock the wheel, the temperature of the wheel at the contact point will rise very quickly, which will reduce the coefficient a lot and make things even .. .