Using the particle model, explain why solids maintain a fixed shape while liquids and gases do not.

Solids have particles that are closely packed together in a fixed arrangement, allowing them to vibrate in place but not move freely. In contrast, liquids have particles that are close but can slide past each other, enabling them to flow. Gases have particles that are far apart and move freely, which allows them to fill any container they occupy.

Graph lens: Read the trend, flat section, gradient, or axis labels before explaining the physical meaning. This question asks: Using the particle model, explain why solids maintain a fixed shape while liquids and gases do not. The correct response is Solids have particles that are closely packed together in a fixed arrangement, allowing them to vibrate in place but not move freely. In contrast, liquids have particles that are close but can slide past each other, enabling them to flow. Gases have particles that are far apart and move freely, which allows them to fill any container they occupy., because gas pressure comes from particle collisions with container walls. In Changes of state, the marking point should connect directly to use the particle model to explain why solids have fixed shapes and liquids and gases flow. If the question includes values, the working must keep the appropriate unit and operation; if it is an explanation, it must name the relevant particle behaviour or energy change. This item belongs to Changes of state and the particle model, so avoid answers that switch to a different quantity, confuse heat with temperature, or describe gas pressure without collisions when collisions are the reason. Checkpoint 195 is distinct because it uses this exact question context and the graph lens rather than a generic particle-model sentence.