# Thread: Went for a spin in a Tesla- holy cow- what a 'Jerk'!

1. ## Went for a spin in a Tesla- holy cow- what a 'Jerk'!

A friend just got delivery of a Tesla... took me for a spin. 0-> 100 in <4 secs.
This was not even 'ludicrous mode' !!
I believe the roadster will do 0-100 in 1sec??

I was not expecting the feeling of all the blood in my heart /gut being slammed backwards (relative to the motion of the car).
It really felt like the scariest bit of a roller-coaster ride.
Got me thinking if It was just the 'acceleration' that made it feel so crazy... or was it the rate-of-change of the acceleration i.e. Jerk, or even some higher-order kinematics- Snap/Crackle/Pop etc

I wonder if anything other than ‘acceleration’ can be actually ‘felt’ by the human body??
Has anyone worked out the Jerk/Snap/Crackle of the Tesla cf other cars??
Do roller-coaster designers use these derivatives?
Are there any countries that police anything other than car velocity/speed? Can you get arrested for accelerating too fast? perhaps for 'Jerking' too fast?? It does actually seem pretty dangerous when you are accelerating so quickly- even if you only end up at 60mph.
Why does gravity work by the 2nd derivative acceleration, not the 3rd or the 4th???

https://agilescientific.com/blog/tag/mechanics
https://en.wikipedia.org/wiki/Jerk_(physics)

G-rant

2. Jerk is rate of change of acceleration and is associated with impacts. Engaging the equivalent of a clutch is a kind of impact! I doubt your estimate of 100 mph in 1 s as the acceleration is in fact limited by the friction tyre to road. Even if it reached 1, the acceleration is limited to 1 g. Thus the limiting v is 32 feet per second (in one second). Melting racing tyres can actually exceed 1 g but I doubt if the Tesla does that. However I agree that the combination of rare earth magnets and lithium batteries has produced a whoosh that seems counter intuitive .

3. Addressing gravity in your last question, the jerk requires change of momentum rather than just a force. You can argue that to get from rest to a finite acceleration in no time is a paradox but that shows how interactions in macro objects does involve both delay and distortion. Even in explosions there is a rate limit.

4. Originally Posted by plant
A friend just got delivery of a Tesla... took me for a spin. 0-> 100 in <4 secs.
This was not even 'ludicrous mode' !!
I believe the roadster will do 0-100 in 1sec??

5. Originally Posted by plant
A friend just got delivery of a Tesla... took me for a spin. 0-> 100 in <4 secs.

I believe the roadster will do 0-100 in 1sec??
The next generation Tesla Roadster's design goal has been said to be 0-100 km/hr in 2.1 seconds for the base model and 1.9 seconds for an upper trim level model.
Other design goals are the 1/4 mile in under 9 seconds and a top speed above 250 mph. Torque measured at the wheels is claimed to be 7,400 lb-ft. Just as a note, that is ridiculously more than can be applied from a standing start, or at any speed. That is enough to enough to spin the tires at any speed, assuming you've got some rpm range left.

The battery will be 200 kWh that will give the Roadster a claimed range of 620 miles at highway speeds.

Originally Posted by profloater
I doubt your estimate of 100 mph in 1 s . . . as the acceleration is in fact limited by the friction tyre to road.
As noted above, it isn't. It will be very quick, but not that quick.

Originally Posted by profloater
. . . as the acceleration is in fact limited by the friction tyre to road.
Perhaps not on this car, depending on the trim level you buy. Tesla has said that an upper trim level of this car will come with 10 cold gas thrusters derived from SpaceX control thrusters. The working pressure of the thrusters will be 10,000 psi. The design intent is to use them to improve performance in cornering, acceleration, top speed, and braking.

6. Originally Posted by Darrell
The next generation Tesla Roadster's design goal has been said to be 0-100 km/hr in 2.1 seconds for the base model and 1.9 seconds for an upper trim level model.
Other design goals are the 1/4 mile in under 9 seconds and a top speed above 250 mph. Torque measured at the wheels is claimed to be 7,400 lb-ft. Just as a note, that is ridiculously more than can be applied from a standing start, or at any speed. That is enough to enough to spin the tires at any speed, assuming you've got some rpm range left.

The battery will be 200 kWh that will give the Roadster a claimed range of 620 miles at highway speeds.

As noted above, it isn't. It will be very quick, but not that quick.

Perhaps not on this car, depending on the trim level you buy. Tesla has said that an upper trim level of this car will come with 10 cold gas thrusters derived from SpaceX control thrusters. The working pressure of the thrusters will be 10,000 psi. The design intent is to use them to improve performance in cornering, acceleration, top speed, and braking.
Wow! To do all that means thrusters all round! I think I would be happy to have under 1 g in all directions! Hats off for the marketing hit though!

7. Kind of puts me off Tesla. What's the point of such ludicrous acceleration? It seems like a fine way to make a person lose control of their vehicle.

Grant Hutchison

8. Originally Posted by grant hutchison
Kind of puts me off Tesla. What's the point of such ludicrous acceleration? It seems like a fine way to make a person lose control of their vehicle.

Grant Hutchison
Yes, its not practical for a normal use vehicle. The original Roadster was their technology demonstrator. Their purpose with it was to show a customer base that generally thought of electric cars as golf carts at best that electric cars could have high performance like ICE cars. They felt, correctly I think, that they needed to overcome a bias against electric cars as serious contenders with ICE cars.

This new generation Roadster is a continuation of that same purpose. It's marketing. It's their super-car, just as most of the major auto manufacturers produce, from Audi to Volkswagen. They'll never make much money off of direct sales of it, if any. It may pay off big though in building / maintaining the Tesla brand.

9. Originally Posted by Darrell
Tesla has said that an upper trim level of this car will come with 10 cold gas thrusters derived from SpaceX control thrusters. The working pressure of the thrusters will be 10,000 psi. The design intent is to use them to improve performance in cornering, acceleration, top speed, and braking.
I found an older article stating each thruster produces 400 lbs., so 4000 lbs. max. This brought the estimated time for 0 to 60 mph down to a little under 1.6 sec., which is amazing for any car. This would, however, average only 1.6 g; not anything to excite a fighter jock having experienced 9 g. What would be ludicrous would be to provide a G-suit for each owner, perhaps not a bad marketing scheme, none the less.

10. Originally Posted by grant hutchison
Kind of puts me off Tesla. What's the point of such ludicrous acceleration? It seems like a fine way to make a person lose control of their vehicle.

Grant Hutchison
And then there's the top speed of 250 mph. That's going to be really useful on a congested freeway.

There was an episode of Top Gear in which one of the presenters was going to drive a supercar with a similar claimed capability on a very large banked circular test track. The manufacturer reps were very nervous because while the car may have been capable of that, the tires were doubtful.

11. I have a tiny motorcycle (250 ninja) that can dust most road car from 0 to 60. It's not capable of 0-60 in 6 seconds, at least I am pretty sure it isn't... People can't really judge how fast they can accelerate and how to keep control of something that is a little squirrelly. I've had people quit racing on me at 45 mph, thinking that both vehicles are going much faster than that. It doesn't feel "fun".

0-60 is kind of not a great comparison for standard road vehicles. What happens after 60 is kind of a crap shoot. My motorcycle starts accelerating like an overloaded truck dragging a parachute. For supercars and race cars, 0-60 makes sense.

12. Big If, if road trains of semi autonomous cars becomes a thing, then rapid acceleration to 60 mph will be useful to join while the system makes a gap for you. It’s a compromise toward driverless, once in the train no driver action is required.

13. Originally Posted by plant
Are there any countries that police anything other than car velocity/speed? Can you get arrested for accelerating too fast? perhaps for 'Jerking' too fast?? It does actually seem pretty dangerous when you are accelerating so quickly- even if you only end up at 60mph.
Our laws to do with traffic rules have an article that says something like you're not allowed to put others in a dangerous situation. I'm sure there are limitations to how that is applied, but accelerating so fast that you're fishtailing out of control over two lanes may well get you in trouble under that article. Which usually means very steep fines, possibly being required to take a very expensive road safety class, or maybe even lose driving license and take lessons and exam again. But controlled acceleration? I don't think that is a problem.

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Originally Posted by grant hutchison
Kind of puts me off Tesla. What's the point of such ludicrous acceleration? It seems like a fine way to make a person lose control of their vehicle.

Grant Hutchison
Roadster is their sports car. No one needs a Ferrari or Corvette on public roads either, really.

The full torque capacity of electric motors at start-up differentiates them from internal combustion engines, though. For a given peak power output, an electric engine will have higher start-up torque.

15. Originally Posted by VQkr
Roadster is their sports car. No one needs a Ferrari or Corvette on public roads either, really.

The full torque capacity of electric motors at start-up differentiates them from internal combustion engines, though. For a given peak power output, an electric engine will have higher start-up torque.
And if you want jerk, you can overvolt the motor, although I would suggest the opposite to avoid jerk forseveral reasons.

16. Originally Posted by VQkr
Roadster is their sports car. No one needs a Ferrari or Corvette on public roads either, really.
Yes indeed. I was expressing doubt that we "need" an electric sports car, and particularly one that delivers that kind of acceleration.

Grant Hutchison

17. Originally Posted by George
I found an older article stating each thruster produces 400 lbs., so 4000 lbs. max. This brought the estimated time for 0 to 60 mph down to a little under 1.6 sec., which is amazing for any car. This would, however, average only 1.6 g; not anything to excite a fighter jock having experienced 9 g. What would be ludicrous would be to provide a G-suit for each owner, perhaps not a bad marketing scheme, none the less.
What I find most interesting about these thrusters is that they are planning on using them to improve handling and braking too. It seems to me that thrusters such as this could significantly increase the range of situations in which a vehicle's safety systems could help avoid an accident. With thrusters spaced all around the vehicle, which is what they plan on doing with the Roadster, and the sensors and software to do so then in all sorts of circumstances in which the vehicle loses traction the thrusters could be used to aid in whatever maneuver is being attempted, to prevent the vehicle from losing control or to stop faster than the tires by themselves would allow.

Perhaps 10 or 20 years from an Emergency Maneuvering System of cold gas thrusters will be a standard safety feature like ABS and airbags.

18. Originally Posted by slang
Our laws to do with traffic rules have an article that says something like you're not allowed to put others in a dangerous situation. I'm sure there are limitations to how that is applied, but accelerating so fast that you're fishtailing out of control over two lanes may well get you in trouble under that article. Which usually means very steep fines, possibly being required to take a very expensive road safety class, or maybe even lose driving license and take lessons and exam again. But controlled acceleration? I don't think that is a problem.
My sister was once stopped and cited for "a show of speed" by local law enforcement because she accelerated around a traffic circle (we call(ed) them rotaries) a bit too hard and her tires spun for a second or two. She never exceeded the posted speed limit, and the conditions were well lit and dry, no traffic or pedestrians. Maybe the officer made it up, but the citation was valid and she had to pay up.

CJSF

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Originally Posted by CJSF
My sister was once stopped and cited for "a show of speed" by local law enforcement....
CJSF
My little brother had a similar experience; he was stopped and cited for spinning his tires on start-up at a traffic light. His citation was for street racing.

20. Originally Posted by CJSF
My sister was once stopped and cited for "a show of speed" by local law enforcement because she accelerated around a traffic circle (we call(ed) them rotaries) a bit too hard and her tires spun for a second or two. She never exceeded the posted speed limit, and the conditions were well lit and dry, no traffic or pedestrians. Maybe the officer made it up, but the citation was valid and she had to pay up.

CJSF
Well technically speaking, she was actually not in full control of the vehicle. If the wheels are spinning then they do not have full traction and that affects handling. But I suspect the officer was making a point of showing his authority rather than actually being concerned about safety.

In the UK, anything that differs from the way a vehicle should be driven can potentially lead to sanction, regardless of the speed involved. There are a multitude of catch all offences available. For example doing a wheelie on a motorcycle is actually quite an art and you must have control that's better than normal riding. But, it's classed as being out of control because it means you are unstable and only have half the braking power.

The Isle of Man has an offence of "driving furiously" which can apply to many situations I suspect.

21. Yes, in the UK wheel-spinning falls under the head of "negligent use of a motor vehicle", for which you can be hit with a £50 fixed penalty notice, but without having your licence endorsed. So basically the lowest level of slap on the wrist, as an encouragement to avoid that behaviour in future.

Grant Hutchison

22. Originally Posted by Darrell
What I find most interesting about these thrusters is that they are planning on using them to improve handling and braking too. It seems to me that thrusters such as this could significantly increase the range of situations in which a vehicle's safety systems could help avoid an accident. With thrusters spaced all around the vehicle, which is what they plan on doing with the Roadster, and the sensors and software to do so then in all sorts of circumstances in which the vehicle loses traction the thrusters could be used to aid in whatever maneuver is being attempted, to prevent the vehicle from losing control or to stop faster than the tires by themselves would allow.
Ah, that would make them far more useful as safety is no small issue given the likely nut behind the wheel, which would be me if I could afford one.

The thruster braking feature is wise, but assuming these are 4-wheel drive, I'm a little surprised they don't already achieve the handling benefits.

23. How does the Tesla compare to the likely new DeLorean?

For example doing a wheelie on a motorcycle is actually quite an art and you must have control that's better than normal riding. But, it's classed as being out of control because it means you are unstable and only have half the braking power.
Much worse than 1/2 the braking power. While on one wheel you have nearly 0 braking power. Any use of the brake while on the rear wheel generates a torque that causes the front wheel to come down, the higher the brake force the higher the torque. Any significant use of the brake causes the front wheel to slam down hard. Often hard enough to overwhelm the front suspension and cause loss of control and an accident. If you really need to brake when you are riding a wheelie you need to have some extra room because you have to first bring the front wheel down in a controlled way and once the bike is stable on 2 wheels, then you can brake.

The Isle of Man has an offence of "driving furiously" which can apply to many situations I suspect.
What a wonderful offence. Another interesting one I heard, from somewhere in the US, was "an ostentatious display of power." All jurisdictions in the US that I've ever known anything about have a variety of violations they can use to cite you no matter how unique your offensive driving behavior may have been. If nothing else they can cite you for "driving dangerously for the conditions" which is up to the discretion of the police officer. You can always challenge it in court of course.

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The electric sports car might be a way to get motorheads to accept electric vehicles. I must admit--it is the old phone booth looking things I think of when I imagine electric cars:
https://www.popularmechanics.com/cars/a1609/4215940/

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