Does acceleration instantly change from zero to a greater number?

[Denken]

Homework Statement

so this isn't really homework but I'm having issues putting it up anywhere else ...

so at the first instant of acceleration, when it is changing from zero to another number ... doesn't that break the theory/law that there is no instanious increase or decrease in accel. because the accel. is changing from zero to a number infinitely times greater.

Homework Equations

The Attempt at a Solution

 

[tiny-tim]

Hi Denken!

It's because most of our equations are for rigid bodies, and there's no such thing as a completely rigid body!

With a real body, there'll always be a finite period when the acceleration increases from zero, but it's so small that we can safely ignore it in practice …

for example, if a block is suspended by string, and the string is cut, the block will have acceleration g, starting with speed zero,

but that's not quite correct, because before it was cut, the bit of string below the cut was stretched slightly, also the bit of the block it was attached to was stretched slightly.

When things are in contact there is a contact force, and a contact deformation, which is so small that we can ignore it in practice, and we can safely use equations in which the acceleration suddenly jumps from zero. ​

 

[Denken]

Thanks for the explanation. :)