Second Law of Motion: Momentum is conserved. Momentum can be defined as mass in motion. Something must be moving to have momentum. Momentum is how hard it is to get something to stop or to change directions. A moving train has a whole lot of momentum. A moving ping pong ball does not. You can easily stop a ping pong ball, even at high speeds. It is difficult, however, to stop a train even at low speeds.
Materials: garden hose connected to a water faucet
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videos are not working for me today?
The quick answer is because the ball still has momentum.
Let’s say you are holding a ball and riding on a train going 25 MPH. That means the train, you, the ball, and even the air inside that train car are also going 25MPH.
As you sit in the train and toss the ball up, that ball is still travelling 25 MPH, just like you. (this is called momentum). So, from your point of view the ball just goes up and down in your hand.
If you need additional information or have follow up questions, please feel free to email [email protected].
Dear Aurora
I have not had an answer to a question in physics I have had forever and can’t answer my son on this either. Could you help please? Why does a ball you throw up in a moving train not shoot to the BACK of the train as you move forward. It still comes down in your hand even when you are not actually where you were a few seconds ago?
Thank you, Eva
The worksheet is correct. One pound is 0.44kg (about half a kg) which means ten pounds would be 4.4kg and 100 pounds is 44 kg.
In the worksheet, it say that 1 lb is 0.4365 kg. Then it says that 100 lbs is 45.36 kg. I think the first one is wrong. Thanks!
the rocket ball launcher is so cool!!!
I would give it a try… anything with wheels like a skateboard or roller skates can work also!
ilana, 11 here! I don’t have a wagon and I wondered if I could make a Lego friends version but my mother thinks it won’t be heavy enough to measure results. What do you think Aurora? Thank you 🙂
Oops – you’re right. That should read mass in motion. Sorry about that!
Just curious — is “inertia in motion” a typo? Should it be “mass in motion”? If not, can you help me understand how what “inertia in motion” means? Thanks in advance!
Minor note: in the advanced student lab worksheet linked from this page (https://www.sciencelearningspace2.com/premiumcontent/docs/Momentum1.pdf), answers are not provided for questions 1-5 (for 1-5, the “solutions” just repeat the questions) – maybe a copy/paste or versioning glitch in the document?
Not having answers probably makes sense for 1-3, since it will depend on the specific items we choose, but it would be great to show at least how the problems should be worked, using variables. For 4 and 5, we know the answers :), but again, it would be great to have those included in the solutions section.
No, acceleration is the rate of CHANGE of the velocity. When your car goes from zero to forty mph, you can do it slowly (like on a bike) or quickly (like in a sports car). The sports car has a faster acceleration than the bike. The velocity is the speed and direction, so 10 mph northwest is your velocity.
would you say that velocity = acceleration ? Thanks.
This unit doesn’t give a full description of Newton’s Laws or terms like inertia. It’s meant to just be an overview of what’s coming. I am sorry if this only caused more confusion for you!
For inertia, check this page out: https://www.sciencelearningspace2.com/2009/09/reading-about-velocity-inertia-newtons-first-law/
and here;s a neat experiment with inertia: https://www.sciencelearningspace2.com/2009/09/tada/
For Newton’s second law, go here: https://www.sciencelearningspace2.com/2009/09/reading-about-acceleration-newtons-second-third-laws/
For Momentum, here’s a couple of cool experiments you can do:
https://www.sciencelearningspace2.com/2009/09/impulse-momentum/
https://www.sciencelearningspace2.com/2009/09/ball-launcher/
https://www.sciencelearningspace2.com/2011/05/rocket-ball-bearing-launcher/
Hope this helps!
Aurora
For older students, there’s an entire section on Newton’s Laws, momentum, inertia, and more here:
https://www.sciencelearningspace2.com/grade-levels/advanced-projects-2/advanced-physics/
I’m having a hard time teaching the second law to my kids because I don’t understand it. Could you help me understand this? You say that momentum is conserved, but what does that mean? How does that relate to a train and ping pong balls? Could you also define inertia for me? You state the law, but what you then show doesn’t seem to connect to the law.
What happens if you try a different computer? The videos play fine over here, but that’s also why we’re updating all the players starting next week. What kind of computer and browser are you using?
2nd video will not play.
The first video is not playing at all.
You need one to be a lot more massive that the other in order for this to work right. 🙂
We tried doing it with 2 tennis balls. Neither of them bounced up; instead, they both went sideways with what seemed like equal velocity. We’re not quite sure what happened. 😛
Yes – we’re currently working on implementing a new player that will work on all devices and need your feedback on it. We’re making changes today – so please check back tomorrow!
Any video in Unit Zero with that particular video player (on the top side “Newtons second law of motion”) is not working sadly, however the second player on the bottom is working fine. It’s a mix of both video players throughout the unit, half working and half not working. Fix any time soon?
It worked!
Great idea! Try it and let me know how it goes! 🙂
what would happen if had two small balls?