# Inertial propulsion, possible ?

1. Dec 21, 2013

### d4rr3n

Above is an old video of a double inclined pendulum device producing unidirectional motion.

Here is a newer but much cruder replication

Physicists however put Inertial propulsion in the same category as perpetual motion, is there really anything in physics that says this should be impossible?

2. Dec 21, 2013

### ZapperZ

Staff Emeritus
Yes! Conservation of energy and conservation of momentum!

I've moved myself across the room by simply waving my arms back and forth while sitting on my office chair mounted on casters, all without having to push off anything. Do you think this is an "inertial propulsion" as well?

Just so you know, this topic is threading on very thin ice, per the PF Rules that you had agreed to. We very seldom allow dubious sources such as this as the topic of discussion.

Zz.

3. Dec 21, 2013

### d4rr3n

Yet both videos clearly show asymmetrical momentum in action...should we ignore the experimental evidence then?

4. Dec 21, 2013

### ZapperZ

Staff Emeritus
No, don't ignore them. However, try to figure out how such things can be explained via conventional means without resorting to such implication there this is unconventional or exotic. Again, do you think I discovered a novel way of propulsion based on what I had already described what I can do?

The reason why we do not allow such a topic for discussion is EXACTLY for the very thing that is happening here. People who bring such topic here are TOO QUICK to jump on the dubious conclusion, all before they learn basic physics and consider all the possible explanations. Are you falling into that same trap?

Zz.

5. Dec 21, 2013

### sophiecentaur

I hope this isn't just another arm waving explanation.

6. Dec 21, 2013

### Kosomoko

In the second video, as the ball rolls down the cart, it is exerting a force that would attempt to push the cart backwards. This force is too small to turn the wheels because whatever bearings they are attached with are not perfect. Thus the force is communicated from the ball to the cart to the bearings to the wheels and then to the Earth, meaning that this does not violate conservation of momentum. When the ball hits the end of the cart, it transfers all of its kinetic energy to the cart in a very small distance, resulting in a large force that is sufficient to turn the wheels. There is nothing very special about what we are seeing here, it is not violating the laws of physics, the ultimate source of the cart's momentum is friction between its wheels and the Earth, the same as would be the case if it were driven by a motor; this is just a very poor way of accomplishing it.

I am not entirely sure what the guy doing the demonstration thought he was proving when he exchanged the ball rolling down with the swinging pendulum. The reason the cart goes farther in that case is because rather than a sharp shock when the ball hits the bottom, there is a more gradual exchange of energy, so less is lost to heat and vibrations in the cart.

The demonstrations in the first video are slightly more complex because the pendulum is driven with a motor, but the principle is the same. If it really were possible to perfectly lubricate the surface so that there is zero friction, the cart wouldn't move. I suspect that the reason the wind up truck spins out of control whereas the pendulum cart doesn't is just because the truck has much more power going to its wheels... due to the fact that turning the wheels of a vehicle directly is a much more efficient way of moving than swinging pendulums around the place.

It is also quite possible that they just cheat by making it so the wheels can't turn backwards.

7. Dec 21, 2013

### sophiecentaur

In a dark, fuzzy bit of film or with second grade equipment it is very easy to cheat (sometimes it's totally subconscious). It's strange that any of these bits of fringe science, you never get a film of NASA or JPL experiments. It's the same with hundred year old inventions. Distance lends enchantment - and believability, if you aren't careful.

If you want examples of the very worst kind of cheating, look at the testing of new drugs that's done by the Pharma companies. Ben Goldacre's Book "Bad Science" makes good reading.

8. Dec 21, 2013

### d4rr3n

Actually you can move yourself across the room in a chair, obviously not with your arms but by rocking back and forth. If you rock back and forth with equal force your chair will simply move back and forth so you get nowhere however if you rock forward forcefully and backwards gently your chair will move forwards.

So momentum is p=mv velocity grater during the forward motion of your body (mass) equates to forward momentum being greater to backward momentum.

Same is happening with an inclined pendulum actually, during half its cycle it is decelerating because it is climbing up a gravity hill and during the other half of the cycle it is accelerating down hill thus net momentum is forward.

9. Dec 21, 2013

### Staff: Mentor

Of course not, but the experimental evidence you point to does not contradict the standard laws of physics taught in every first semester introductory physics class. This is basic Newtons laws with standard static and kinetic friction.

This is such basic standard stuff that people claiming it represents something groundbreaking come off as tending towards the mentally insane side of the crackpot spectrum.