Newton's Third Law

32 viewed last edited 11 months ago
Chris Matthews
When you push a wall, it pushes you back... but how? The wall doesn't physically move at all, so how does it push you back? Lastly, when you push a wall or door, it doesn't really move (it stays firm). BUT, when you push, let's say Jell-O, it moves. Is it because the atoms aren't attracted to each other as strong in Jell-O as they are in a door or wall?
Mahesh Godavarti

I think you asked two questions:

  1. When you push a wall, how does the wall push you back?
  2. Why is Jell-O malleable whereas a rock or wall is not?

Here is an image that describes the interaction between the wall and you.

There are three sets of interactions. You push against the floor and the floor pushes against you. You push against the wall and the wall pushes against you. And finally, the wall pushes against the floor and the floor pushes against the wall. I think this is much easier to understand, if you imagine yourself pushes against your twin instead of a wall as shown below.

I hope this answers your first question. I will post the answer to the second question next.

Presence of gelatin makes Jell-O malleable. Gelatin is basically processed collagen, which is a structural protein in animals' connective tissue, skin, and bones. Structurally, collagen is composed of three polypeptide chains that are wound together into an -helix--like three strands of spaghetti twisted together--and held together by hydrogen bonding. When collagen is heated in water, the triple helix unwinds and the chains separate, becoming random coils that dissolve in water: That's gelatin. As the gelatin cools, the molecules try to regain the original helical structure and eventually bond together as they lose energy.
Mahesh Godavarti

A non-malleable solid is a solid because the molecules are tightly held together and cannot move relative to each other.

A malleable solid is where molecules are connected to each, but can move relative to each other.

Jell-O is special. It is malleable solid holding a liquid inside its malleable structure. Imagine a watery sponge held in an airtight ziploc bag. You can squeeze the resulting object and change its shape, however, the water is always locked into the sponge.

Following examples, give you the best idea of malleable and non-malleable solids.

Image you have three identical copies of the wrench below.

Let's say we tie three of them together. Like so:

You will notice that the resulting object is still solid, but the three wrenches can rotate freely at the joints letting the object attain any one of multiple possible shapes. This would be equivalent of a sponge.

But now, let's say we tie them like so:

Then the resulting object is rigid and cannot change shape. This would be the equivalent of a solid wall or door.

Hope this helps.