The key is that the random motion of particles is *balanced* within the object.
Imagine a bunch of people pushing and pulling randomly on a box. If they all push with the same force in different directions, the box won't move. The forces cancel each other out.
This is similar to the random motion of particles. While each particle is moving, the net effect of all these movements is zero. Here's why:
* Equal and opposite forces: The particles are constantly colliding with each other. Each collision involves two forces that are equal in magnitude and opposite in direction. These forces cancel each other out.
* Random directions: The particles are moving in random directions. Any movement in one direction is likely to be balanced out by movement in the opposite direction.
This balance is what keeps the object at rest.
However:
* Temperature: If you increase the temperature of the object, the particles move faster and with more force. This can disrupt the balance, causing the object to expand.
* External forces: If you apply an external force to the object, it can overcome the balanced forces of the particles and cause the object to move.
Let me know if you have any other questions!
