Very interesting example I'm 68 years old and I guess the only example was with the 5 steel balls which that is very interesting and it also shows this theory is true. Thanks for sharing!
Dear Bruce, your channel is fantastic! I have used some of your ideas in my teaching and I admire your handyman skills. One small note about this video though is that it is important to emphasize that the pair of forces in Newton's 3rd Law act on different objects and so they do not, cannot cancel each other out. When you pull the force meter in two directions, those forces are not a pair according to Newton's 3rd as they both act on the same object (the force meter). In fact, they could make the meter accelerate, if one of them were bigger.
Thank you soo much sir ... I couldn't understand the 3rd law until I saw this ....I would recommend this video to my friends who find it hard to understand...
Thank you sir i finally know why we can jump forward becz we apply a force backward .And u use the skateboard example to proof that there is really a force apply backwards .thanks a lot sir .
What I love about Newton's 3rd law is that when you jump and apply a force backwards on the earth, you and the earth experience the same force, which means the earth technically accelerates a tiny amount, although it's negligible due to the mass of the earth. But still, that old Chuck Norris joke about pushing the earth down when he does push-ups is actually true, and I find that very cool!
That joke about Chuck Norris pushing the Earth down when he does push-ups is true for everyone. It's impossible to push yourself without pushing something else simultaneously. The Earth is just so massive that you do negligible work on it, when you push the Earth down. The Earth reflects your work back onto you, since you are the one who experiences positive work done.
An interesting question to ask students at 4:07 is, that if the sheet under the car moves back one foot, what distance would the pencils move back? My Yeany , congratulations once more.
Hello Carmel Pule, Just wanted to say thank you for all the positive comments that you've added recently. I appreciate all the kind words and suggestions that you've posted on several of my videos.
If we can approximate the pencils as rolling like cylinders without skidding on either top or bottom, then the pencils should move backwards 6 inches, after the cardboard moves back one foot. In reality, there inevitably will be roll with slip, so it won't be exactly half.
Hey, Bruce! Thanks for all you've done to produce these videos and share your great tools for teaching physics. I've made my own versions of a number of your devices and found them extremely useful. I do have a criticism of this video. I wonder if some of these (especially the scale examples) reinforce the misconception that Newton's third law says that any force an object will be opposed by an equal force on that same object. For example, you talk about pushing down on the scale, and, as a result, the table pushes up on the scale with the same size force. While this is true, this isn't an artifact of Newton's 3rd. Newton's 3rd would say that as you push down on the scale with more force, the scale pushes up on you with more force. If there was a rule that every time you applied a downward force to an object, there would be an equal-magnitude upward force on that same object, then it would be impossible to have unbalanced forces on anything and all objects would always have constant velocity. I'm also unsure of why you're trying to sell students on the idea that you can't move forward when jumping off the skateboard. While it isn't huge, you do clearly have some forward motion in the video. You must have had a forward force acting on you from the skateboard. The skateboard, in turn, got a backward force acting on it from you, and accelerated backward as a result. You certainly could jump farther forward in this scenario, it just gets more dangerous (think cartoon banana peel). As you accelerated forward more, the skateboard would accelerate backward more. You can mitigate the danger by using a more massive skateboard. I have sets of skateboard wheels attached to the bottom of a long 18 inch wide strip of plywood, which also allows me to simply walk forward to demonstrate the backward force applied to the skateboard. I love the last demo in this video (the car on the cardboard on pencils) - that really gets at the heart of Newton's 3rd in a scenario that is normally impossible to see. Why on Earth would a student believe me when I tell them that as their car accelerates from rest, the ground pushes the car forward and the car pushes the ground backward? This demo is such clear evidence of that! Thank you again for all you've done with this! Andrew
Thanks Andrew, that video was one of the first ones I made and I eventually plan to redo it. The skateboard is better done outside with safety equipment on, I've had kids try and jump forward while standing on it but since it has such a small mass in comparison to their own, they can kick the board backwards quite a distance but are unable to move any measurable distance forward no matter how hard they try and jump. We put a line down on the ground and they try to jump over it, anyone that does gets a free lunch, in 40 years I've never had to pay out. I have a heavy mass that I can add to it, or I have them throw a shot-put backwards, in either case they can then drive themselves forward. But jumping and walking forward off the board are two different situations. When you step forward off the board you'll notice that part of your body moves backwards, trying to jump forward off the board is a much different scenario and doesn't work.
Thanks for the response! I like having them throw something from on the skateboard, too. With my giant skateboard, I have one student stand on the board and throw a medicine ball to a student in front of them on the ground, and vice versa. In both cases, the skateboard moves. Then I have both kids on opposite ends off the skateboard and pass the ball back and forth. The skateboard rolls while the ball is in air, but stops as soon as the ball is caught. We also use this as a way to discuss the difference between exchanging momentum between parts of a system and transferring momentum into or out of a system. I saw you present at an NSTA conference years ago. That really got me started thinking about how I could create simple, cheap, and effective devices for experiments and demonstrations to help my students. I've done a great deal of that since then, and am a better teacher for it. Thank you!
There are all sorts of variations and it sounds like you have a really good one, thanks for sharing it, guess I'll have to get a bigger board. Those NSTA conferences goes back quite a few years and were a lot of fun, at the time Science Kit and Boreal labs were sponsoring a few teachers to give workshops for them. Money got a lot tighter and that was dropped. I still do ones that are close enough to drive to. You made my day knowing that someone remembered them.
Perfect example of why space travel with rockets does not work. The hot fuel that pushes out at the back has no mass to push against in the vacuum of space. So no forward momentum is created.
my car doesn't have a motor on it and when i do the example the cardboard moves forward not backwards, does that still work for the third law of motion(I have to present this tomorrow so i would appreciate if someone would answer quickly)
No. The table isn’t pushing. You are. The table is just there. 2:50-You did not jump the same way you did without the skateboard. 3:30-No, the car is not trying to push the table backwards. Talking that way is absolute deception. Or at best irresponsible.
First point: Bruce is the source of energy to compress the springs in the scale, but the scale relies on both the table and Bruce to push it in order to compress it from both sides. It relies on the table being there to supply a constraint force. Second point: Try this for yourself, and see if you can jump beyond that line, when taking off from a skateboard. Third point: Yes, the car is trying to push the table backwards, despite your objection. The car cannot push itself forward on its own. The car attempts to do work on the table (which is attached to Earth), but it isn't successful at doing any work of any significance on the table and Earth, because of how massive Earth is relative to it. But applying a force to the table wasn't completely futile for the car, because the table reflects this force back onto the car, as a Newton's third law pair. It is this force of the table pushing the car forward, that makes the car move forward. The car's internal motor is the source of the energy, while the Earth and table are the source of the momentum.
Very interesting example I'm 68 years old and I guess the only example was with the 5 steel balls which that is very interesting and it also shows this theory is true.
Thanks for sharing!
Wow
I've spent 4 days watching videos that only explain the action and reaction part, thanks for this
Dear Bruce,
your channel is fantastic! I have used some of your ideas in my teaching and I admire your handyman skills. One small note about this video though is that it is important to emphasize that the pair of forces in Newton's 3rd Law act on different objects and so they do not, cannot cancel each other out.
When you pull the force meter in two directions, those forces are not a pair according to Newton's 3rd as they both act on the same object (the force meter). In fact, they could make the meter accelerate, if one of them were bigger.
Thanks Dave, I'm not sure if I agree with this part either and plan to redo it. Funny thing is I pulled that part out of a science book
Thank you soo much sir ...
I couldn't understand the 3rd law until I saw this ....I would recommend this video to my friends who find it hard to understand...
happy to hear it helped
Thank you sir i finally know why we can jump forward becz we apply a force backward .And u use the skateboard example to proof that there is really a force apply backwards .thanks a lot sir .
Buen video Fabri,
A tope con la física como siempre
Buena fabri
thank you so much, this helped with my sci project!
good
smde
This is very useful. Helped me a lot with my homework.
Same
yet another simple easy to understand explanation. Nice one.
What I love about Newton's 3rd law is that when you jump and apply a force backwards on the earth, you and the earth experience the same force, which means the earth technically accelerates a tiny amount, although it's negligible due to the mass of the earth. But still, that old Chuck Norris joke about pushing the earth down when he does push-ups is actually true, and I find that very cool!
That joke about Chuck Norris pushing the Earth down when he does push-ups is true for everyone. It's impossible to push yourself without pushing something else simultaneously. The Earth is just so massive that you do negligible work on it, when you push the Earth down. The Earth reflects your work back onto you, since you are the one who experiences positive work done.
An interesting question to ask students at 4:07 is, that if the sheet under the car moves back one foot, what distance would the pencils move back? My Yeany , congratulations once more.
Hello Carmel Pule, Just wanted to say thank you for all the positive comments that you've added recently. I appreciate all the kind words and suggestions that you've posted on several of my videos.
If we can approximate the pencils as rolling like cylinders without skidding on either top or bottom, then the pencils should move backwards 6 inches, after the cardboard moves back one foot. In reality, there inevitably will be roll with slip, so it won't be exactly half.
Hey, Bruce! Thanks for all you've done to produce these videos and share your great tools for teaching physics. I've made my own versions of a number of your devices and found them extremely useful.
I do have a criticism of this video. I wonder if some of these (especially the scale examples) reinforce the misconception that Newton's third law says that any force an object will be opposed by an equal force on that same object. For example, you talk about pushing down on the scale, and, as a result, the table pushes up on the scale with the same size force. While this is true, this isn't an artifact of Newton's 3rd. Newton's 3rd would say that as you push down on the scale with more force, the scale pushes up on you with more force. If there was a rule that every time you applied a downward force to an object, there would be an equal-magnitude upward force on that same object, then it would be impossible to have unbalanced forces on anything and all objects would always have constant velocity.
I'm also unsure of why you're trying to sell students on the idea that you can't move forward when jumping off the skateboard. While it isn't huge, you do clearly have some forward motion in the video. You must have had a forward force acting on you from the skateboard. The skateboard, in turn, got a backward force acting on it from you, and accelerated backward as a result. You certainly could jump farther forward in this scenario, it just gets more dangerous (think cartoon banana peel). As you accelerated forward more, the skateboard would accelerate backward more. You can mitigate the danger by using a more massive skateboard. I have sets of skateboard wheels attached to the bottom of a long 18 inch wide strip of plywood, which also allows me to simply walk forward to demonstrate the backward force applied to the skateboard.
I love the last demo in this video (the car on the cardboard on pencils) - that really gets at the heart of Newton's 3rd in a scenario that is normally impossible to see. Why on Earth would a student believe me when I tell them that as their car accelerates from rest, the ground pushes the car forward and the car pushes the ground backward? This demo is such clear evidence of that!
Thank you again for all you've done with this!
Andrew
Thanks Andrew, that video was one of the first ones I made and I eventually plan to redo it. The skateboard is better done outside with safety equipment on, I've had kids try and jump forward while standing on it but since it has such a small mass in comparison to their own, they can kick the board backwards quite a distance but are unable to move any measurable distance forward no matter how hard they try and jump. We put a line down on the ground and they try to jump over it, anyone that does gets a free lunch, in 40 years I've never had to pay out. I have a heavy mass that I can add to it, or I have them throw a shot-put backwards, in either case they can then drive themselves forward. But jumping and walking forward off the board are two different situations. When you step forward off the board you'll notice that part of your body moves backwards, trying to jump forward off the board is a much different scenario and doesn't work.
Thanks for the response! I like having them throw something from on the skateboard, too. With my giant skateboard, I have one student stand on the board and throw a medicine ball to a student in front of them on the ground, and vice versa. In both cases, the skateboard moves. Then I have both kids on opposite ends off the skateboard and pass the ball back and forth. The skateboard rolls while the ball is in air, but stops as soon as the ball is caught. We also use this as a way to discuss the difference between exchanging momentum between parts of a system and transferring momentum into or out of a system.
I saw you present at an NSTA conference years ago. That really got me started thinking about how I could create simple, cheap, and effective devices for experiments and demonstrations to help my students. I've done a great deal of that since then, and am a better teacher for it. Thank you!
There are all sorts of variations and it sounds like you have a really good one, thanks for sharing it, guess I'll have to get a bigger board. Those NSTA conferences goes back quite a few years and were a lot of fun, at the time Science Kit and Boreal labs were sponsoring a few teachers to give workshops for them. Money got a lot tighter and that was dropped. I still do ones that are close enough to drive to. You made my day knowing that someone remembered them.
buen video Fabri
Okay, but how do you prove the reaction force is equal magnitude? That's not obvious
Another great video Bruce, thank you !
I am being forced to watch this by my teachers
Pay attention. Listen in classes. It will help in the future so you don’t have to keep going back to grade 6 level simplicity videos
@@airconditioningunit9777 Then why are you here? HMMMM
@@ParadoxHit cause i didn’t listen in class. My advice is from my experience
i admire you, nice work!
thank you!
Perfect example of why space travel with rockets does not work. The hot fuel that pushes out at the back has no mass to push against in the vacuum of space. So no forward momentum is created.
how many times did you fall when you jumped on the skateboard?
Awesome, thank you.
my car doesn't have a motor on it and when i do the example the cardboard moves forward not backwards, does that still work for the third law of motion(I have to present this tomorrow so i would appreciate if someone would answer quickly)
I'm in tears now
No. The table isn’t pushing. You are. The table is just there.
2:50-You did not jump the same way you did without the skateboard.
3:30-No, the car is not trying to push the table backwards. Talking that way is absolute deception. Or at best irresponsible.
shut.
First point:
Bruce is the source of energy to compress the springs in the scale, but the scale relies on both the table and Bruce to push it in order to compress it from both sides. It relies on the table being there to supply a constraint force.
Second point:
Try this for yourself, and see if you can jump beyond that line, when taking off from a skateboard.
Third point:
Yes, the car is trying to push the table backwards, despite your objection. The car cannot push itself forward on its own. The car attempts to do work on the table (which is attached to Earth), but it isn't successful at doing any work of any significance on the table and Earth, because of how massive Earth is relative to it. But applying a force to the table wasn't completely futile for the car, because the table reflects this force back onto the car, as a Newton's third law pair. It is this force of the table pushing the car forward, that makes the car move forward. The car's internal motor is the source of the energy, while the Earth and table are the source of the momentum.
Rockets are good example of Newton’s third law
Nice jump
2020 got teachers lacking
Why don't you try to run fast and hit a brick wall? Let's see what happens.
I've had both knees replaced, I can't run fast, jog is the best I could do
Omg 😯 I found Jeffree Star’s GRANDPA OMG ITS TRUEEE #noeyebrows
I don't think so