Background: Another thing we can see in this animation is that particles are constantly colliding with one another. One assumption that we make when talking about collisions between gas particles is that they are completely elastic collisions. In an elastic collision , momentum is conserved, which means that none of the kinetic energy of the colliding particles is lost in some other form (such as the emission of light). This makes sense, because if energy were lost in collisions, the speeds of the particles would gradually decrease over time, and eventually everything would condense down into a solid form.

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: Which sample would have elastic collisions, sample A or sample B?
Answer: sample A

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: Which sample would not have elastic collisions, sample A or sample B?
Answer: sample B

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: In which sample the momentum would be conserved, sample A or sample B?
Answer: sample A

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: In which sample the momentum would not be conserved, sample A or sample B?
Answer: sample B

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: Would momenturm be conserved or not conserved in sample A?
Answer: conserved

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: Would momenturm be conserved or not conserved in sample B?
Answer: not conserved

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: Would kinetic energy in sample A be lost or retained?
Answer: retained

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: Would kinetic energy in sample B likely be lost or retained?
Answer: lost

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: Which sample's kinetic energy likely be lost, sample A or sample B?
Answer: sample B

Situation: Dan is in his physics lab. He is experimenting with colliding particles. He has two samples of particles, sample A and sample B. Sample A contains gas particles, but sample B does not contain gas particles.

Question: Which sample's kinetic energy likely be retained, sample A or sample B?
Answer: sample A