Science Buddies: "Ask an Expert"

As we all know unit of acceleration is m/s.s so for calculation of very short time as in micro seconds the value of acceleration could go as high as beyond the speed of light c.
So I just want to know that how it will be possible to attain more velocity than c (however if we talk over acceleration it means there is velocity equal to it if applied for one second).

divyanshu9 - I'm afraid you are mixing apples and oranges in this case. Velocity or speed or even the speed of light is a distance measurement of an objects movement over time. It is expressed in terms of inches/hour (inches per hour), feet/second, miles/hour, miles/day or furlongs/fortnight. Acceleration or deceleration is the rate of change of velocity over time. It is expressed in units such as feet/second/second, or miles/second/second or kilometers/hour/hour and so on. It is a rate of change of velocity or speed. Even if we look at acceleration change over a very short period of time - milliseconds, microseconds, nanoseconds for example, it is still an expression of the rate of change of velocity. We all accept that nothing can have a velocity faster than the speed of light (about 300 million meters/second). Your phrase that the value of acceleration could exceed the velocity of light is mixing two different kinds of values. You can't add quarts to feet or subtract temperature from pounds.

Rick Marz

First thing how can you say that. It is expressed in units such as feet/second/second, or miles/second/second or kilometers/hour/hour and so on. We all know that acc. due to gravity is 9.8m/s^2.
yesterday i was solving a electrostatics question.t
The two large plates having some surface charge density are placed parallel to each other having separation 2.00cm. A electron starting from rest near one plate reaches other plate in 2.00 microsecondseconds, the acc. of electron coming in this case is 10^10 m/s^2 , so if this acc. go for one second it velocity will reach for 10^10 m/s isn't it?.
And one thing more what can be the maximum change in velocity that can occur for any matter,when we saying change in velocity we also keep in mind that sometime the velocity must be greater than or equal to that change in velocity. vfinal - v initial=v suposs, supppse v got some value as x so vfinal must have value greater or equal to x,equals in case when v initial is zero.

divyanshu9 - Perhaps I am misunderstanding your comments. I don't think anything in my first reply was incorrect in terms of physics. I don't understand your statement that an electron moving between two parallel plates spaced 2 mm apart achieves 10^10 m/second velocity. How did you calculate that? Clearly that velocity is beyond the speed of light (3.0x10^8 m/sec). To suggest that acceleration in any system continues at a constant rate (from your 2 microsecond example to 1 second, as you hypothesized) isn't necessarily true. Other factors certainly may act on the object and change velocity. Other conditions may change. Please clarify what you don't understand in my response, or why you think I am in error. Perhaps others might understand your issue and respond better.

Rick Marz

In your previous reply you stated the unit of acc. As feet/ sec , first tell me the dimention of accelaration its L/T×T . but according to your unit feet/sec its L/T which is dimention of velocity.
I case of the question use formula S=ut + 1/2a t^2 you will get accelaration 10^10 m/s^2.