Law of Inertia - Newton’s 1st Law of Motion

A demo on the Law of Inertia, aka Newton's 1st Law of Motion. What happens when you hammer a knife into a potato or an apple? Video inspired by Dr. Erukhimova :)

[black.sasuke.uchiha]

I was halfway expecting her to hammer her own thumb by accident😬💀

[dionnelong]

You’re simply the best! 👍🏽 I chop often! 🙏🏽

[qwazaqwazaq]

if you do not study at school, then the whole world will be filled with magic and fantasy

[ironbutterfly]

It depends on the speed. If the speed is enough to overcome static friction and switch to sliding one. Newtons laws need to be always applied in context of friction theory.

[CryptoBoostOfficial]

I think it is Newton's 3rd law as every action has an opposite reaction and she is saying that this is the first law of motion. What's your opinion guys please let me know.

[aaryawarik]

she explains better than phys teacher tysmm!

[jennymarx]

You're explaining in the best way possible! 😺 Tq

[austinjenkins]

This video doesn’t explain it completely but she is correct that it has something to do with inertia. Inertia is an objects resistance to a change in motion and is a property of mass. The more mass the more inertia. Remember that equation Force = mass x acceleration? That also plays in here. The knife is accelerated downwards fast enough and therefore exerting a downwards force that overcomes that of the static frictional force between the potato and the knife and because of the potato’s mass and therefore inertia it does not get moved with the knife but remains relatively in the same place. After the knife moves through the potato, frictional force then keeps the potato in its new position. If you tried this with a much smaller potato that would have the same friction coefficient but much less inertia, the same effect would not take place. Not unless you hit the knife much harder to accelerate it faster through the smaller potato. Hope this helps anyone who is still confused.

[jeremybrown]

This is how we hang axe handles. You hit the end of the handle to knock the head on, not the axe head itself

[zxk]

You can do this to attach hammers, axe heads, etc, to handles, too.

[-ShahdMohamedShamseldinElshabk]

that actually helped thanks I have a physics quiz tmr abt that

[ROUSHDYABAZA-bq]

Ok... There is reaction effect due to knocks
Cit the apple and take measures inside over knife limits it's different not equal easy because weight is differs as the apple up

[techin]

This indicates that the friction between the potato and the knife is less than the force applied by the hammer. 😇 In this case the knife moves relative to the knife. That doesn't mean the potato is not moving.😢 Actually, the potato does move relative to any objects expect those experiencing the force, like the table.🙃

[alparslanesmer]

In fact it was not gravity, it was Newton's energy that pulled the apple at his head.

[Cilyvanilly]

Okay but why does it split at how do we know at what speed or force the apple will split ?

[TheShawnMower]

Moving the knife with your hand also apples force. I mean applies force. But the apple doesn't slide up.

The dofferent friction and the rate of acceleration that really makes this more complete.

[Lesserthannone]

There is a force acting on the apple. Gravity also rulesout being stationary. Friction of the surface of the knife in the apple holds the apple in place. Transferring mechanical force of impact via hammer over comes the friction in the direction of the hammers swing. Then the friction once again overwhelms gravity and any movement. Inertia has little to nothing to do with why people are impressed.


The fruit isn't jumping up the knife. The knife is diving deeper into it, simultaneously your muscles and tendons are lowering the relative position of all of the objects and pulling them back up. In reality both the knife and fruit should move in the direction of the hammers inertia until otherwise acted on. I still don't understand how this is meant to demonstrate the property of inertia when friction is doing the heavy lifting.

I feel my autistic brain intuition leaves me unimpressed and confused as to what the fuss is about. I'm still surprised at siphoning, that's some strange and bewildering behavior.

[Crazias]

So the potato doesn't move only knife moves right?

[shrinjanachoudhury]

When motivation and distraction come from the same place

[asthadas]

This seems easy to cut apples thanks for the idea..👀