# Perpetual motion machine

#### bobsmith1492

##### Diamond Member
A couple of inventors brought in a purported perpetual motion machine today. It consisted of two huge pistons sliding back and forth over two magnets. It made a ton of commotion and looked pretty cool, but since it was radiating a ton of heat and shaking their truck trailer back and forth, there's no way it was "generating more energy than it consumed" like they claimed.

I feel sad for the guys, though; they are so convinced. Somehow, if they think about it in a certain way, they can generate energy from nothing. I was hoping my boss could straighten them out but I think they were pretty stuck in their ways. They seemed to have been very emotionally invested in the thing which can good but not when it comes to science or engineering.

#### IHateMyJob2004

##### Lifer
Try to figure out a way to have gravity be the driver for a perpetual machine.

I got stuck at this:
feet per second squared. Convert that to the units of energy. I couldn't figure it out.

#### bobsmith1492

##### Diamond Member
Originally posted by: IHateMyJob2004
Try to figure out a way to have gravity be the driver for a perpetual machine.

I got stuck at this:
feet per second squared. Convert that to the units of energy. I couldn't figure it out.
Hint: there's no such thing as a perpetual motion machine.

Feet/sec^2 would be acceleration - acceleration due to gravity. To get to energy, you'd need an object's mass and altitude; then energy would be height x mass (or weight...)

#### slugg

##### Diamond Member
Originally posted by: bobsmith1492
Originally posted by: IHateMyJob2004
Try to figure out a way to have gravity be the driver for a perpetual machine.

I got stuck at this:
feet per second squared. Convert that to the units of energy. I couldn't figure it out.
Hint: there's no such thing as a perpetual motion machine.

Feet/sec^2 would be acceleration - acceleration due to gravity. To get to energy, you'd need an object's mass and altitude; then energy would be height x mass (or weight...)
height x weight, not mass.

weight = mass * acceleration...

That is, weight is the force of acceleration (gravity) on a mass. Newton's 2nd...

Mass is independent of weight. This is why an object 10 meters high on Earth has more potential energy than the same object being 10 meters high on the Moon. The acceleration is of smaller magnitude...

Not to be annoying, but this is the highly technical forum

#### EricMartello

##### Senior member
The closest thing I've seen to perpetual motion is like this:

There is a ramp with a slight incline, a magnet at the top of the ramp, a hole in front of the permanent magnet, and a steel BB at the bottom. The magnetic force pulls the BB up the ramp, but once the BB gets to the hole it falls down the hole and onto a chute. The magnetic force cannot overcome the pull of gravity to support the BB without assistance from the ramp, so the BB falls through the hole, down a chute and resets at the base of the ramp. The process repeats.

Of course, this isn't really generating any energy but it is demonstrating what seems to be...perpetual motion. I think the BB needs a nudge to get it going, but once it starts it keeps going indefinitely. The momentum of falling down the chute lasts long enough for it to reach the magnet and get up the ramp.

#### bobsmith1492

##### Diamond Member
Originally posted by: slugg
Originally posted by: bobsmith1492
Originally posted by: IHateMyJob2004
Try to figure out a way to have gravity be the driver for a perpetual machine.

I got stuck at this:
feet per second squared. Convert that to the units of energy. I couldn't figure it out.
Hint: there's no such thing as a perpetual motion machine.

Feet/sec^2 would be acceleration - acceleration due to gravity. To get to energy, you'd need an object's mass and altitude; then energy would be height x mass (or weight...)
height x weight, not mass.

weight = mass * acceleration...

That is, weight is the force of acceleration (gravity) on a mass. Newton's 2nd...

Mass is independent of weight. This is why an object 10 meters high on Earth has more potential energy than the same object being 10 meters high on the Moon. The acceleration is of smaller magnitude...

Not to be annoying, but this is the highly technical forum
Thanks Slug (timely name, speaking of mass...) It's been a while since physics class. So, potential energy does have to do with the acceleration due to gravity.

Eric - even that system would not be perpetual. Friction from the air and against anything the BB touches will slow it down, eventually bringing it to a halt.

#### TuxDave

##### Lifer
Originally posted by: EricMartello
The closest thing I've seen to perpetual motion is like this:

There is a ramp with a slight incline, a magnet at the top of the ramp, a hole in front of the permanent magnet, and a steel BB at the bottom. The magnetic force pulls the BB up the ramp, but once the BB gets to the hole it falls down the hole and onto a chute. The magnetic force cannot overcome the pull of gravity to support the BB without assistance from the ramp, so the BB falls through the hole, down a chute and resets at the base of the ramp. The process repeats.

Of course, this isn't really generating any energy but it is demonstrating what seems to be...perpetual motion. I think the BB needs a nudge to get it going, but once it starts it keeps going indefinitely. The momentum of falling down the chute lasts long enough for it to reach the magnet and get up the ramp.
Did you actually see the physical product or did you just see a drawing of the idea?

#### reallyscrued

##### Platinum Member
Originally posted by: EricMartello
The closest thing I've seen to perpetual motion is like this:

There is a ramp with a slight incline, a magnet at the top of the ramp, a hole in front of the permanent magnet, and a steel BB at the bottom. The magnetic force pulls the BB up the ramp, but once the BB gets to the hole it falls down the hole and onto a chute. The magnetic force cannot overcome the pull of gravity to support the BB without assistance from the ramp, so the BB falls through the hole, down a chute and resets at the base of the ramp. The process repeats.

Of course, this isn't really generating any energy but it is demonstrating what seems to be...perpetual motion. I think the BB needs a nudge to get it going, but once it starts it keeps going indefinitely. The momentum of falling down the chute lasts long enough for it to reach the magnet and get up the ramp.
Wouldn't the BB just attach to the magnet before falling through the chute? Or once a few milimeters down the chute, wouldn't the bb just stick to the wall as the magnet tries to pull the bb toward it?

#### EricMartello

##### Senior member
Originally posted by: bobsmith1492
Eric - even that system would not be perpetual. Friction from the air and against anything the BB touches will slow it down, eventually bringing it to a halt.
Maybe, but I don't see how. I mean the BB is falling the same distance through the hole, down the chute and back to the base of the ramp. It means the velocity is constant with each cycle...well...as constant as the pull of gravity on the BB. Friction does slow it down but the magnet and gravity should provide adequate compensation for it. I should build one of these and see how long it runs...I'm also curious to know at which point in the cycle the BB is gradually slowed each time it passes.

Originally posted by: reallyscrued
Wouldn't the BB just attach to the magnet before falling through the chute? Or once a few milimeters down the chute, wouldn't the bb just stick to the wall as the magnet tries to pull the bb toward it?
You're probably thinking of a small BB. BB = ball bearing, they come in lots of different sizes and weights. For this experiment to work you would have to use a steel BB that is about 5-8mm in diameter. Also, it takes less energy to pull the BB up the ramp than it does to suspend the full weight of the BB in mid air, which is why it will not stick to the magnet before falling down the hole in front of the magnet.

Originally posted by: reallyscrued
I like the idea of this better -

I saw something like this before. That wheel will spin for a long time but it does eventually stop, because the BBs in that device have to overcome the friction of the wheel itself and not only their own.

#### f95toli

##### Golden Member
Originally posted by: EricMartello
Friction does slow it down but the magnet and gravity should provide adequate compensation for it
No, of course they can't "compensate" for it. Friction means that the system is losing energy meaning you have to add energy from OUTSIDE the system in order to keep it running, i.e. it is not a PM.
Neither gravity nor magnetism can create energy; just store it.

#### EricMartello

##### Senior member
Originally posted by: f95toli
Originally posted by: EricMartello
Friction does slow it down but the magnet and gravity should provide adequate compensation for it
No, of course they can't "compensate" for it. Friction means that the system is losing energy meaning you have to add energy from OUTSIDE the system in order to keep it running, i.e. it is not a PM.
Neither gravity nor magnetism can create energy; just store it.
The ball falling down the chute = gaining kinetic energy.

The thing would operate for a long time, but eventually the magnets would wear out or the mass of the BB would diminish, etc. Wear and tear would stop it before friction does.

#### reallyscrued

##### Platinum Member
Originally posted by: EricMartello

Originally posted by: reallyscrued
Wouldn't the BB just attach to the magnet before falling through the chute? Or once a few milimeters down the chute, wouldn't the bb just stick to the wall as the magnet tries to pull the bb toward it?
You're probably thinking of a small BB. BB = ball bearing, they come in lots of different sizes and weights. For this experiment to work you would have to use a steel BB that is about 5-8mm in diameter. Also, it takes less energy to pull the BB up the ramp than it does to suspend the full weight of the BB in mid air, which is why it will not stick to the magnet before falling down the hole in front of the magnet.
No matter the size, if you had a magnet powerful enough to pull the ball from the bottom of the plane, it will be powerful enough to keep the ball from falling through the chute. In your example, I think you are imagining the magnetic force becoming stronger stronger as the ball rolls closer but then when the ball reaches the hole, the magnet's attraction suddenly disappears?

I'm not trying to put you down, it's a creative idea, but in reality I don't think it would work. You would need some kind of electromagnet that you can cut the power to once the ball reaches the chute, but of course, having an electromagnet defeats the purpose of it running without any external power.

If you still insist that it is possible, I challenge you to try or show me a working model. I believe you are bending the laws of physics in your head to make it work out the way you see fit.

#### EricMartello

##### Senior member
Originally posted by: reallyscrued
No matter the size, if you had a magnet powerful enough to pull the ball from the bottom of the plane, it will be powerful enough to keep the ball from falling through the chute. In your example, I think you are imagining the magnetic force becoming stronger stronger as the ball rolls closer but then when the ball reaches the hole, the magnet's attraction suddenly disappears?

I'm not trying to put you down, it's a creative idea, but in reality I don't think it would work. You would need some kind of electromagnet that you can cut the power to once the ball reaches the chute, but of course, having an electromagnet defeats the purpose of it running without any external power.

If you still insist that it is possible, I challenge you to try or show me a working model. I believe you are bending the laws of physics in your head to make it work out the way you see fit.
No, the magnetic force does not disappear when the ball reaches the hole...but the force of gravity acting on the ball increases since it is no longer being supported by the ramp. Also, you could put a buffer in front of the magnet to ensure that the ball would never actually come close enough to the magnet to "stick" to it. Using an electromagnet would defeat the whole purpose of this being a "perpetual motion" machine...and I'm not saying it IS perpetual motion, but it sure seems to be. I have some neodymium magnets. I might whip one of these together just to see if I can get it working. If nothing else it would make one neat little coffee table decoration.

#### reallyscrued

##### Platinum Member
Originally posted by: EricMartello
No, the magnetic force does not disappear when the ball reaches the hole...but the force of gravity acting on the ball increases since it is no longer being supported by the ramp. Also, you could put a buffer in front of the magnet to ensure that the ball would never actually come close enough to the magnet to "stick" to it. Using an electromagnet would defeat the whole purpose of this being a "perpetual motion" machine...and I'm not saying it IS perpetual motion, but it sure seems to be. I have some neodymium magnets. I might whip one of these together just to see if I can get it working. If nothing else it would make one neat little coffee table decoration.
Negative. The force of gravity remains constant throughout the entire loop. I will reiterate, if the magnet is powerful enough to make the ball overcome the friction between the ball and the ramp created by the force of gravity, it will be powerful enough to make the ball stand still at one position, either by attaching to the magnet itself or being suspended in the middle of the chute.

#### f95toli

##### Golden Member
Originally posted by: EricMartello

The ball falling down the chute = gaining kinetic energy.
Indeed, but while doing so it is also losing POTENTIAL energy (reemmber that the sum of potential+kinetic energy is constant); and since you need to raise the ball to the same height again in order to be able to repeat the cycle there is no net gain of energy than can compensate for the energy lost due to friction.

#### silverpig

##### Lifer
Originally posted by: f95toli
Originally posted by: EricMartello

The ball falling down the chute = gaining kinetic energy.
Indeed, but while doing so it is also losing POTENTIAL energy (reemmber that the sum of potential+kinetic energy is constant); and since you need to raise the ball to the same height again in order to be able to repeat the cycle there is no net gain of energy than can compensate for the energy lost due to friction.
Ahh good old L = T - V

#### Born2bwire

##### Diamond Member
Originally posted by: silverpig
Originally posted by: f95toli
Originally posted by: EricMartello

The ball falling down the chute = gaining kinetic energy.
Indeed, but while doing so it is also losing POTENTIAL energy (reemmber that the sum of potential+kinetic energy is constant); and since you need to raise the ball to the same height again in order to be able to repeat the cycle there is no net gain of energy than can compensate for the energy lost due to friction.
Ahh good old L = T - V
Pffft... Lagrangian, how quaint. Hamiltonian is where it's at bitches! H=L+V

#### Veramocor

##### Senior member
Originally posted by: bobsmith1492
A couple of inventors brought in a purported perpetual motion machine today. It consisted of two huge pistons sliding back and forth over two magnets. It made a ton of commotion and looked pretty cool, but since it was radiating a ton of heat and shaking their truck trailer back and forth, there's no way it was "generating more energy than it consumed" like they claimed.

I feel sad for the guys, though; they are so convinced. Somehow, if they think about it in a certain way, they can generate energy from nothing. I was hoping my boss could straighten them out but I think they were pretty stuck in their ways. They seemed to have been very emotionally invested in the thing which can good but not when it comes to science or engineering.
What type of company do you work at that crackpots bring their PM machines to you?

#### JesseKnows

##### Golden Member
Originally posted by: bobsmith1492
... It made a ton of commotion and looked pretty cool, but since it was radiating a ton of heat and shaking their truck trailer back and forth ...
Which are specific examples of how it was losing energy to the outside: noise, heat, more heat in the truck springs.

#### Red Squirrel

##### No Lifer
I have this idea in mind for a somewhat perpetual motion device but no time or resources to build it. I don't think it would be true perpetual, but it would need some "help" but greatly amplify what is helping it go. It sounds like it would work, but somehow, it probably does not. You can't generate more energy then what you're using to generate it.

#### blahblah99

##### Platinum Member
All perpetual motion machines I've seen so far have absolutely NO mathematical formulas to prove that the contraption works. To do so, it would have to violate the laws of thermodynamics.

#### QuantumPion

##### Diamond Member
The best idea for a perpetual motion machine, which took me considerable time to understand its failings, is this:

Imagine a very tall U-shaped container, one side filled with fresh-water and the other with salt-water. The bottom is separated by a reverse-osmosis filter, and the top ends of the tube are touching with a lid. The containers are tall enough such that the weight of the water provides sufficient pressure for the reverse-osmosis process to occur. Since salt-water is denser then fresh-water, its level will be lower then the fresh-water given a fixed system volume. As the salt-water passes through the filter, the level of the fresh-water side rises, causing the excess to spill back over into the salt-water side, thus forming a self-sustaining flow loop from which work can be extracted.

#### bobdole369

##### Diamond Member

wide cylinder on its side - Think massive fuel tank for the shape, or hamster wheel.

At the hub of this cylinder place holders that extend into the cylinder and hold a permanent magnet fast with N and S poles facing out of the device.

Now place another permanent magnet on the wheel itself. The repulsion should force the free magnet up the slope created by the floor of the wheel, creating potential energy released when gravity brings the magnet down.

Some form of ratcheting or grip tape or guides need to keep the potential energy from disappearing and force the free magnet to rotate the wheel. I'm sure it would reach a steady state.

#### bobdole369

##### Diamond Member
Imagine a very tall U-shaped container, one side filled with fresh-water and the other with salt-water. The bottom is separated by a reverse-osmosis filter, and the top ends of the tube are touching with a lid. The containers are tall enough such that the weight of the water provides sufficient pressure for the reverse-osmosis process to occur. Since salt-water is denser then fresh-water, its level will be lower then the fresh-water given a fixed system volume. As the salt-water passes through the filter, the level of the fresh-water side rises, causing the excess to spill back over into the salt-water side, thus forming a self-sustaining flow loop from which work can be extracted.
isn't that how ocean currents basically work?