Everyday Physics

Science In The Kitchen

Have you ever wondered

  • why your mom or dad fuss about not being able to find their favorite kitchen knife?
  • Why are chopping board surfaces rough and not smooth?
  • why milk does not boil over and flow out even during the busiest morning hours?
  • how is the water so cold in the ancient-shaped matka in the kitchen without it being in the fridge? Mom said it is made of mud!
  • how does milk magically turn into curd or paneer that you love so much?

There is much more science in the kitchen than elsewhere in the entire household. Everything you eat or drink get created and transformed through applying basics of science.

Lets begin with the potato fries that you love so much you wouldn’t mind carrying it in your tiffin everyday. The finger-like pieces are all more-or-less of the same shape and size, and mom (or dad) do the chopping in a jiffy even as you are struggling to dress up! How do they do it?

Chopping the potatoes needs a knife with a sharp edge, a good handle to grip well so that the person using it does not get hurt by the sharp blade, a surface (chopping board) to keep the potatoes so that they don’t slip off while chopping. The material of the knife needs to be a hard one such as stainless steel or iron so that it does not bend while chopping, and handles are normally made of wood.



There are two basic physics principles involved –

  • Force applied to a small confined area can become strong enough to break molecular or surface bonding, break apart objects
  • A small force applied at one end of a Lever can magnify to a large force at the other end of the Lever

Let us explore in detail.

If you were to press the knife into kneaded dough, it would make a mark like a fine line. The fine line is in the shape of V-wedge, if you see up close. The pressure that is applied along this line is what rupture the surface bond of the potatoes. Once a small break is made, it grows bigger with the continuing force, and the two pieces separate out.


Another way to understand this force is – if you use a bag with thin or rope like shoulder straps, they hurt your shoulders due to force from the weight of the bag being applying to a small area of your shoulders. If you use a bag with broader straps, they do not hurt as much since the force gets distributed over a larger area.

The handle and the blade form a Lever – pressure applied to the handle transfers to the blade. The handle is of a smaller length than the blade, yet the force gets transferred to the blade due to Lever action.

Coming back to the magic of almost equal sized potato fingers – with practice, the knife blade can be positioned at equidistant points so that equal sized pieces can be cut. And the favorite knife is favorite because it has a good grip perfect for someone’s hands, a sharp fine blade and allows chopping with the least amount of effort.

If you want to try your hand at chopping, do it under supervision of your parents.

Think about why chopping boards have a rough surface and not a smooth one.



This post was contributed by Susmita Narayan.


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