Physics Question! Is my understanding correct?

[adamsaccount]

Ok thanks i'll get writing

 

[Stabinbac]

A Joule is a Newton per metre, not the other way around. It's J = N*m.

Newton meter. Not Newton per meter. Newton per meter would be N/m.

Sweet, would you need to put some sort of gyroscope into the bolts to make them fly straight though?

Gyroscopes work in space
http://www.liveleak.com/view?i=fa1_1270309990

A bunch of other cool space videos by Don Pettit:
http://www.youtube.com/playlist?list=PL39E2wNYUl1hZUs3PMdygWIqjcQYwyRCy

 

[2xDouble]

Just being a pedant here, but you can lift a car. That's technically what you're doing when you use a car jack. Or indeed when you push a car up a hill.

And with a sophisticated system of pulleys, it should be more than possible for one guy to properly lift a car.

It is possible for a human to lift a car without those mechanisms. It's a popular and dangerous feat in strong-man acts and competitions. The car is lifted along the edge of the frame (thus utilizing a small mechanical advantage rotating against the far-side tires). Though only one side of the car is actually lifted and by only a few inches, it is quite impressive to see live. Professional wrestler/strongman Marc Henry performed the stunt in many shows during his tenure with WWE.

 

[Darken12]

A Joule is a Newton per metre, not the other way around. It's J = N*m.

Newton meter. Not Newton per meter. Newton per meter would be N/m.

Foreign language quirk, sorry.

 

[lechat]

Sweet, would you need to put some sort of gyroscope into the bolts to make them fly straight though?

Possibly, as its air resistance that causes the bolt to fly straight, any slightly off centre momentum would go unchecked and the bolt would tumble end over end.

Cheers, i guess the Wookies were onto something there

i'd say it's possible it wouldn't fly straight . take a look at this slow motion arrow
without aerodynamics to straighten the arrow that flex you see there would more than likely have the arrow spinning if it wasn't perfectly symmetrical

 

[adamsaccount]

Yeah well my whole idea kind of got shat on when a google search told me that guns work in space too, unless were talking about medieval knights orbiting pluto and why the hell not?

 

[AJvsRonin]

I imagined the bolt tumbling instead of the pointy end staying forward since theres no air for the arrows to direct it through

No, it would tumble if there was a force that would push it backwards. Otherwise our rockets would tumble all the way to the moon and Mars instead of going in a straight line.

Rockets can tumble, that's why many have thrust gimbaling, to compensate and adjust direction of thrust to keep it directly under the centre of mass.

There is something kinda trying to push it backwards (well its really just fighting forward momentum), inertia. It's a similar idea to a rear wheel drive car trying to drive on ice. Rear end is trying to go forward, front end is heavy and doesn't want to go anywhere, a slight imbalance on one side or a little more grip on one tyre than the others and you have an imbalance between centre of thrust and centre of mass, not enough friction to correct for it and the car spins out.


A somewhat decent explanation:
http://www.apogeerockets.com/downloads/Newsletter239.pdf

 

[Anakinnnn]

Hi all physics minded folks.

I'm writing a story and one of the characters is an engineer. This is just a scene where the characters are sitting in an SUV talking while they wait. The engineer character (Character 2) is a smart guy, but not some super genius but tends to ponder a lot and put forth weird ideas that seem nonsensical to a lay person.

This idea is loosely based on an idea I had while talking to an engineer friend of mine but she's a civil engineer so wasn't sure of the details.

Here's the conversation:

Character 1: I?m not sure I understand.

Character 2: It?s all just different ways of expressing energy as a value using the laws of thermodynamics. Right now you are being pulled against the seat by gravity. If you weigh around 60 kilograms this is roughly six hundred newtons of force being applied against the seat and floor. One newton is equal to one joule per metre. A joule is roughly the amount of energy required to lift an apple one meter up in the air, and the amount of energy released when the same apple is dropped by a metre. Using a standardised amount of chemical energy in a food, say that soda you?re drinking, we can express the amount of energy in something as a value against that standard. This car weighs about a thousand kilograms, that drink has around eight hundred kilojoules of chemical energy. So divide the first number by the second number and you just drank enough chemical energy to lift this car 8 centimetres into the air, or just over three inches.

Character 1: Awesome. So why can?t I lift a car then?

Character 2: Not my fault, ask a biologist.

END

Now funnily enough I'm a biologist and from what I could find out this is roughly true but I know I haven't taken into account things like acceleration etc.

So, does this work/is it true? For my comfort could you list any qualifications, university degree etc so I can rest comfortably knowing an expert has checked over this? I asked the reel physics guys but they never replied.

Thanks!

Heya AJvsRonin,
I saw our show name listed here and was wondering how I missed your original question posed to us? I surely would have responded if you asked us a direct question. Sorry if it somehow got missed in the forums or crazy emails we get.
As for your story above, I love the dialogue... good stuff. As for an answer to your question of whether that is possible, I am not sure what the actual question is and I am more than happy to help answer if I can.
Thanks!
Jason Dean
REEL PHYSICS

 

[AJvsRonin]

-snip-

Character 2: It?s all just different ways of expressing energy as a value using the laws of thermodynamics. Right now you are being pulled against the seat by gravity. If you weigh around 60 kilograms this is roughly six hundred newtons of force being applied against the seat and floor. One newton is equal to one joule per metre. A joule is roughly the amount of energy required to lift an apple one meter up in the air, and the amount of energy released when the same apple is dropped by a metre. Using a standardised amount of chemical energy in a food, say that soda you?re drinking, we can express the amount of energy in something as a value against that standard. This car weighs about a thousand kilograms, that drink has around eight hundred kilojoules of chemical energy. So divide the first number by the second number and you just drank enough chemical energy to lift this car 8 centimetres into the air, or just over three inches.

-snip-

Heya AJvsRonin,
I saw our show name listed here and was wondering how I missed your original question posed to us? I surely would have responded if you asked us a direct question. Sorry if it somehow got missed in the forums or crazy emails we get.
As for your story above, I love the dialogue... good stuff. As for an answer to your question of whether that is possible, I am not sure what the actual question is and I am more than happy to help answer if I can.
Thanks!
Jason Dean
REEL PHYSICS

Hey Jason!

No worries mate, I'm sure you guys get a lot of weird and random questions and can't get to them all.

In short the question is: Is character 2 correct from a physics stand point? Correct both in the underling principle and in the math that he uses?

I'm getting conflicting numbers depending on how I look at it, some calculators say the car will be lifted 8cm, others 80m!

I just think the underlying idea could be an interesting one and a good way of educating people about kinetic, potential and chemical energy (and how much energy really is in our food!), maybe somebody could make some kind of online calculator where you could convert forces to food: i.e. "A car with a mass of x kilograms hits a wall travelling at y speed and is stopped. This is equal to the chemical energy in z Big Macs." Or "A hand grenade explodes using x joules, this is equal to y number of twinkies."

I'm really enjoying the show. Keep up the good work.

AJ