Physics 8 Lesson 20: Are atoms and molecules moving or at rest?
1. Theoretical summary
1.1. Brown’s Experiment
1827 – The botanist (British) Berao observed pollen grains in water with a microscope and discovered that they were in constant motion in all directions.
When pounded or boiled, the pollen grains are still in constant chaotic motion.
That experiment is called the Brown experiment.
1.2. Atoms and molecules are in constant motion
– Explain the movement of pollen grains in Berao’s experiment.
- Water molecules are in constant motion, while in motion it collides with the pollen grains from many directions, these collisions are not balanced, causing the pollen grains to be in constant chaotic motion.
The cause of the movement of the pollen grains in the Berao experiment is that the water molecules are constantly at rest but in constant motion.
Conclusion: Atoms and molecules are in constant chaotic motion.
1.3. Molecular motion and temperature.
– When the temperature of the water increases, how will the pollen grains move?
The faster the water molecules move, the stronger the collision with the pollen grains makes the pollen grains move more strongly.
The motion of atoms and molecules is closely related to temperature, so this motion is called thermal motion.
Conclusion: The higher the temperature, the faster the atoms and molecules that make up the object move.
2. Illustrated exercise
2.1. Form 1: Explain the phenomenon of the motion of molecules
Put some potassium permanganate seeds in one cup of cold water and one cup of hot water. Observe what happens and explain.
After a while the whole cup of water turns purple and the cup of hot water happens faster.
Because there is a distance between the water molecules and the potassium permanganate, they are in constant motion.
The movement of molecules is faster when the temperature is higher so that the potassium permanganate is dissolved in water and the hot water cup happens faster.
2.2. Form 2: Explain whether diffusion occurs faster with increasing temperature
Does diffusion happen faster with increasing temperature? Why?
Diffusion occurs faster as the temperature increases because as the temperature increases the molecules move faster.
⇒ Substances merge themselves more quickly.
3.1. Essay exercises
Question 1: What is diffusion?
Verse 2: What happens when the temperature decreases?
Question 3: Why does sugar dissolve faster in hot water than in cold water?
Question 4: Diffusion occurs with which substance?
3.2. Multiple choice exercises
Question 1: Choose the correct statement about the motion of molecules and atoms?
A. Molecules, atoms are sometimes moving, sometimes stationary.
B. Atoms, molecules move in a certain direction.
C. The higher the temperature of an object, the slower the atoms and molecules that make up the object.
D. The faster the atoms and molecules that make up the object, the higher the temperature.
Verse 2: The velocities of molecules are related to which of the following quantities?
A. Mass of the object
B. The temperature of the object
C. Volume of the object
D. Specific gravity of the object
Question 3: Choose the right word to fill in the blank.
Phenomenon …… is the self-melting of atoms and molecules of substances due to thermal motion.
A. dissociation B. motion C. oscillation D. diffusion
Question 4: Which of the following is not a property of atoms or molecules?
A. incessant motion.
B. sometimes moving, sometimes standing still.
C. There are distances between atoms and molecules.
D. The faster the motion, the higher the temperature.
Through lecture Atoms, molecules moving or at rest? Here, you need to accomplish some of the goals that the lesson gives, such as:
Show an analogy between the motion of a giant balloon due to the motion of Berao.
Understand that the faster the molecules and atoms that make up an object move, the higher the temperature of the object.
Explain why the higher the temperature, the faster the diffusion occurs.