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Velocity and acceleration 
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#1
Sep905, 10:57 PM

P: 20

Is it possible to have an INCREASING speed AND have the MAGNITUDE of acceleration decreasing????
If so please give examples. I asked my TA this question today and she did not know the answer...???? Help! 


#2
Sep905, 11:04 PM

P: 266

velocity will increase if acceleration is still positive



#3
Sep905, 11:06 PM

P: 20

yes but is there a situation where you can have increasing speed, but decreasing magnitude of acceleration????



#4
Sep905, 11:06 PM

P: 266

Velocity and acceleration
yes, as long as a is still positive



#5
Sep905, 11:50 PM

P: 20

i don't understand...if a is positive and decreasing then you cannot have increasing speed??? explain it to me like i'm 4 years old....



#6
Sep905, 11:53 PM

P: 266

if you are going 6m/s in the x direction and accelerate int the x direction 2m/s^2 you will speed up, and if you move your acceleration down to 1m/s^2 you will continue speeding up but at a slower rate.



#7
Sep1005, 12:04 AM

P: 20

yes i understand that...but for instantaneous velocity and acceleration it is not possible right??? when you accelerate 2 m/ss both speed and accel are increasing, but when you slow down by 1 m/ss then your speed and accel are both decreasing...??



#8
Sep1005, 12:08 AM

P: 266

nah, you're still increasing



#9
Sep1005, 12:57 AM

Sci Advisor
P: 2,510

This actually is rocket science! If you are in the Shuttle, and you're burning the engines to go to higher orbit or something, you might do a fullthrottle burn for a certain distance, and then back off gradually. So, at first you accelerate with about 4 G's, and later you are only accelerating at about 1 G.
At 4 G's, you might look at your groundspeed indicator and see that, for every second you continue that burn, you go almost 130f/s faster than you were going the previous second. As you throttle back through 2G's, you'll see that you only gain 64f/s for every second you stay at that setting. And when you ease it down to 1G, you'll notice that you're going 32f/s faster for every second you coninue. Yet, even at 1G, you're still accelerating (@32f/s). So, your magnetude of acceleration has decreased from 4G's through 3 and 2, to 1G, but you were allways accelerating. You just started out accelerating hard, and ended up only accelerating a little. 'Zat make any sense? 


#10
Sep1005, 07:04 AM

Mentor
P: 41,436

Be careful with directions and signs though. It may be that your speed is actually decreasing, if you were traveling in the negative direction. If your acceleration changes from 2 m/s^2 to 1 m/s^2, then you are still speeding up! Just not as quickly. Only when the acceleration goes to zero do you stop accelerating. If it goes negative, then you'll start slowing down. 


#11
Sep1005, 03:57 PM

Sci Advisor
P: 1,082

Freshman calculus provides the answer. That is, acceleration is he rate of change of velocity. true in any frame of reference That's all she wrote.
Regards, Reilly Atkinson 


#12
Sep1005, 06:48 PM

P: 20

Doc Al, I think I understand the way you put it, however, does the word "magnitude" not imply an "absolute value" for acceleration? I have been leaning toward YES as being the answer to my question, but you saying NO has thrown me for a loop.
So the answer is NO, because if you decrease acceleration from 10 to 1, you are still increasing your speed, but your acceleration is decreasing??? 


#13
Sep1005, 10:18 PM

Sci Advisor
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#14
Sep1105, 12:37 AM

P: 266




#15
Sep1105, 07:33 AM

Mentor
P: 41,436




#16
Sep1105, 06:17 PM

Sci Advisor
P: 1,082

I plead stupid. As long as the accelleration stays positive, velocity can increase  but at a decreasing rate. If, for example, I go from 32ft/sec/sec to 10ft/sec/sec the speed does continue to increase. My most humble apologies for failing a first year calculus exam.
Regards, Reilly Atkinson 


#17
Jan1110, 04:20 AM

P: 2

Whereas velocity the time rate of change of position of a body in a specified direction, acceleration is rate of increase in speed. So irregardless of the speed of a body IE: 50 ft per minute, 1000 miles per hour, etc.. that change in velocity to a different value is either acceleration or deceleration (decrease). Acceleration values change depending on the time over which the change in speed occurs. I can increase my speed very slowly (.001g) or very quickly (10g) to get from 10 mph to 20 mph, but in both instances I am accelerating, only at different rates. The difference will be demonstrated in the time it will take to get to the higher speed, but both will cause acceleration to the higher speed.



#18
Jan1310, 09:38 AM

P: 250




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