Impulse

Impulse is the change in momentum caused by a Force.

Impulse is also the time integral of force.

That means the impulse is the same whether a large force is applied over a short period or if a small force is applied over a long period.

Formulas

Impulse = \(\int F.dt\)
Impulse = \(\Delta p\) = \(mv \: - \: mu\)

Karate chop example

Q: Is it the impulse or the force that actually breaks an object?

• Change in momentum (Applied Impulse) in a short span breaks the object (F = (mv-mu)/t)
• Using more time for the change in momentum will make the force lower
• But using the same Applied Force for a longer duration would increase the Applied Impulse

So what is the best way to Karate chop?

Once the board is cracked, the rest of the propagation is due to the shock wave.

We use knife hand rather than fist.

So the pressure also is important, as all the force is acting on a small area to create a crack.

Ultimately it seems the change in momentum by time taken, or a force, that breaks up a brick. Think of it as a sudden jolt in a structure, giving them no time to regroup before the force breaks all joints.

To Read in Impulse

• https://physics.stackexchange.com/questions/149482/impulse-and-force-in-a-karate-chop-can-we-maximize-force-minimizing-the-time-of
• https://physics.stackexchange.com/questions/270030/newtons-3rd-law-hitting-drywall-which-i-break-vs-hitting-a-brick-which-br
• https://physics.stackexchange.com/questions/512334/the-physics-of-board-breaking
• https://physics.stackexchange.com/questions/517580/what-happens-when-a-weapon-breaks-on-impact
• https://www.physicsclassroom.com/class/momentum/Lesson-1/Real-World-Applications