We all must have come across the specification of ' Zero to Maximimum Speed' ie called Acceleration Time or 'Pick Up ' of the bike. I would call it the 'Response Time' for the Maximum Speed. It is the ('0 to 120/100 or so km/hr in 6 secs' ) or something similar. This means that the bike would take a time period of 6 secs to start from 0 km/hr ie standstill to attain the maximum possible speed of 120 km/hr. I could not understand what is the reason for this time lag. wait....wait , you guys may think that I dont even know that friction on ground, the air drag etc would play a role, but then actualy my question is " Why does it take time for a accelerating a mass ( here the bike) to a said speed starting it from standstill" 1. "Why cant be the process instantenous? 2. Why is this response time needed? 3. I actually wanted to very minutely understand the concept of Acceleration which we all have taken for granted to be dv/dt ie rate of change of velocity. But my question is " How do we decide the response time -- here the term dt during the change of velocity of a mass from V1 to V2 , if the process becomes almost instantenous. Wait i will give an example of a instantenous velocity change Example : Consider a block of mass M with wheels moving on rails. The block is connected to another smaller tray behind it with a welded rod between the two ie the block and the tray. The tray is also on wheels on the same rail, such that the block and the tray form one unit and the tray moves along the block when the block moves as they are joined by the rod. On the tray is a system which ejects a jet of air which hits the rear face of the block applying a Force to it which causes the block to move forward ( and along it moves the tray, so that the same intensity and flowrate of the jet is maintained as the distance between the block and the tray remain the same throughout). So as the same Force is exerted on the block throughut during one particular flowrate of the jet, then just imagine that if the jet is first locked by plate at the nozzle mouth and all of a sudden the plate is removed, then the jet would hit the block all of a sudden with all the Force INSTANTENOUSLY, ie dt = 0, causing the block to gain a speed of say V1 m/s, then , " How would we calculate dv/dt in such a case., when there is no 'Response Time' ie the the full intensity of the force is applied in one shot. First say the jet exerts F1 and in another case F2 such that F1> F2 and both act in a sudden ejection ie one -go zzoommm- fashion on the block with full intensity in one shot. In Second case velocity is sayV2. My question is : 1. Does it always require a Response Time to gain a certain velocity from zero, and if so WHY? ( even if you say Inertia, then why some time, why not instantenous? ) Neglect friction, drag etc. Recall the bike example. 2. How to calculate the Acceleration in such a case if the rise in velocity is almost Instanenous, then does the rate of change in velocity from zero to respective max. speeds for F1 and F2 be measurable? ie how quickly has the velocity changed from zero to max -- is it measurable? If Yes or No then How? because a = dv/dt Can anyone explain this in detail Please what happens to the VELOCITY and ACCELERATION on a micro level of TIME GAP when the Force ( F =M.A) acts on the body INSTANTENOUSLY with NO LAG at all. And note that the FOrce ( of te Jet) use do cause this motion has an ACCELRATION term in it ie F=M.A Sorry for the very long question, but couldnt help as had to give a detailed example. Please respond to it ansd clear a very Findamental Concept for me. Thanks in Advance, -Rohan.