What is true about kinetic energy?

Responses-

a) Molecules within a substance have kinetic energy when that substance moves.

b) Cold molecules have potential energy but no kinetic energy, as kinetic energy is experienced as heat.

c) Molecules of liquids and gases are in constant motion, so they have kinetic energy.

d) All molecules are in constant motion, so they all have some kinetic energy.

All of the responses are true.

c) Molecules of liquids and gases are in constant motion, so they have kinetic energy.

The correct answer is c) Molecules of liquids and gases are in constant motion, so they have kinetic energy.

To understand this concept, let's break down the options and explain how to arrive at the correct answer:

a) Molecules within a substance have kinetic energy when that substance moves.
This statement is partially correct. When a substance as a whole moves, its molecules also move, and they possess kinetic energy. However, this is not the whole picture. Even when a substance is not moving as a whole, the molecules within it can still be in motion, and therefore, have kinetic energy. Therefore, this option does not fully capture the nature of kinetic energy.

b) Cold molecules have potential energy but no kinetic energy, as kinetic energy is experienced as heat.
This statement is incorrect. Kinetic energy is not solely related to heat. Molecules can possess kinetic energy regardless of their temperature. Even at low temperatures, molecules are still in motion, and therefore, still have kinetic energy.

c) Molecules of liquids and gases are in constant motion, so they have kinetic energy.
This statement is correct. Molecules in liquids and gases are not fixed in position. They are constantly in motion, moving and colliding with each other. This motion indicates that they possess kinetic energy.

d) All molecules are in constant motion, so they all have some kinetic energy.
This statement is also correct. All molecules, regardless of their state (solid, liquid, or gas), are in constant motion. The motion of molecules is a fundamental characteristic of matter, and it implies the presence of kinetic energy.

Therefore, the correct answer is c) Molecules of liquids and gases are in constant motion, so they have kinetic energy.