If you’ve ever travelled in a car, you’ll know it’s always better when acceleration and braking manoeuvres are executed as smoothly as possible. This smooth action occurs when the driver depresses and releases the accelerator or brake pedal gently and not roughly. When braking, experienced drivers will slowly take their foot off the brake shortly before the car comes to a halt, thereby reducing the energy of the deceleration. Ideally, the car will then stop without “jerking” to a halt. During an emergency braking manoeuvre, when the braking distance needs to be as short as possible, drivers will keep their foot pressed down hard on the brake until the car comes to a stop. This causes everyone in the vehicle to be thrown backwards with force when the car stops, because deceleration drops from maximum to zero from one moment to the next.
The significance of jerk in automation.
If you want to move the carriage of a Linear Unit, you need to factor in jerk.
Jerk indicates the period of time t it should take to achieve a desired acceleration a.
Where 
The unit of jerk is 
If, for example, you want to achieve acceleration of 
within 0.5 s, you will need jerk to be 
.
However, if you indicate that you want to start a motion with an acceleration of 
and you do not enter anything under jerk, this means that the desired acceleration will be achieved, in theory, after an infinitely short period of time.
In mathematical terms, that is equivalent to dividing by 0: 
In such an instance, jerk would theoretically be infinitely large.
In reality, this is not possible, as performance limits and inertia mean the motor has to build up acceleration over a period of time that, although short, is always going to exceed 0. Thus jerk, although very large, is finite.
If the goods to be transported are sensitive or a liquid, inputting acceleration without stating jerk means they can be damaged or, in the case of liquids, can lap over the edge of an open container. Inputting a motion without stating jerk can also subject mechanical components to extreme stress, as all the components involved in the motion will attempt to provide the desired acceleration in as short a space of time as possible.
The benefits that come from indicating jerk include less strain on both the load being transported and the mechanism itself. Furthermore, a motion with jerk is less noisy than one without. The disadvantage is that the motion takes longer to execute and involves a longer travel distance.
.
