Theoretically...

Stonedofmoo

Stonedofmoo

Stonedofmoo

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...if you could run a car without air resistance, i.e. no air at all just gravity (ignoring the fact the engine needs air for a minute)

Would a 1hp car eventually go as fast as a 1000hp car if geared the same? :confused:
 
You mean would it keep pace (i.e. have the same acceleration) with the 1000hp car?

In which case - no.

Force = mass * acceleration

Assuming the cars have the same mass, the 1000hp car will always be going faster - as there is no more issues with top speed (and we're going to ignore all other issues such as friction / heat etc.)
 
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No because top speed is still determined by the point where the power required to overcome drag equals that produced by the engine.

Although you've got rid of the biggest form of drag (air resistance) there are still others to overcome such as frictional losses in the drivetrain, rolling resistance of tyres etc.
 
Stonedofmoo said:
...if you could run a car without air resistance, i.e. no air at all just gravity (ignoring the fact the engine needs air for a minute)

Would a 1hp car eventually go as fast as a 1000hp car if geared the same? :confused:
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no, removing air won't make your Pulsar as fast as screwmodded 306TD!

Tom.
 
Borris said:
You mean would it keep pace (i.e. have the same acceleration) with the 1000hp car?
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i think he means the top speed.

Air resistance isn't the only thing to overcome when powering a car, theres mechinaical drag which will increase as the speed increases due to heat

edit: too slow :(
but taking out all of the drag factors you would be able to hit the top speed.
 
gearing a 1hp car with the same as a 1000hp car would result in probably no take-off at all - the power would all be swallowed up (and lost) in the transmission
 
Nope the 1000bhp car will have the higher top speed. Even with getting rid of air resistence you still have the resistence from the tyres and drivetrain.

Top speed is reached where the driving power = resistence. Which the 1000bhp the driving power is 1000 times higher so will go faster.
 
saitrix said:
Top speed is reached where the driving power = resistence. Which the 1000bhp the driving power is 1000 times higher so will go faster.
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Not really. Top speed can easily be dictated by the gearing. Rally cars for example will only hit 110-115mph hitting the limiter in top gear, as for most stages they are geared low.

If the car is geared for a higher top speed then the power of the engine can propel the car then yes you're right.
 
olv said:
Not really. Top speed can easily be dictated by the gearing. Rally cars for example will only hit 110-115mph hitting the limiter in top gear, as for most stages they are geared low.

If the car is geared for a higher top speed then the power of the engine can propel the car then yes you're right.
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I was ignoring gearing, i was showing why certain cars cannot hit the limiter in their top gear. It is the extra resistive force due to the engine having a smaller moment on the driving wheels and the shear extra friction involved.

I do know how gearing works, thanks.
 
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I think the 1bhp vs. 1000bhp is a bit extreme for a decent example because of how HP is actually created (hp = (lb/ft-torque*rpm)/5252 meaning that torque and revs would play a part in creating those two figures which in turn would mean different engine characteristics, and therefore different rev ranges, frictional losses, etc. etc.), but considering that, in a theoretical environment where all things mechanical are equal then the 1bhp car should be capable of being geared to produce the same theroretical top speed as the 1000bhp car and if such theoretical conditions allowed both cars to reach the required engine speed, then they would match in top speed.

In the OP's post, he mentions gravity, which causes friction, so in that instance, no they wouldn't reach the same top speed, even though the gearing and potential maximum rpm may produce a theroetically matching top speed.

Theoretical top speed is really dependant upon the gearing and the maximum revs. Horsepower and weight only comes into play in the real world where physics begins to get in the way.
 
This is like a thing I saw on the Discovery channel a while back. It was a method of powering a space ship in space, it used (I think it was called) an Ion Drive. This was a tiny engine that on earth could barely power a car, but given time in space, with nothing to slow it, it would reach speeds closing on the speed of light.
 
saitrix said:
I was ignoring gearing, i was showing why certain cars cannot hit the limiter in their top gear. It is the extra resistive force due to the engine having a smaller moment on the driving wheels and the shear extra friction involved.

I do know how gearing works, thanks.
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i wasn't suggesting you didn't. But i was just pointing out that the 1000bhp car wouldn't be faster as you said, seeing as though the OP said geared the same.
 
GlasgowTitan said:
This is like a thing I saw on the Discovery channel a while back. It was a method of powering a space ship in space, it used (I think it was called) an Ion Drive. This was a tiny engine that on earth could barely power a car, but given time in space, with nothing to slow it, it would reach speeds closing on the speed of light.
Click to expand...

I remember seeing an interesting documentary about space crafts using sun sails. Apparantly the energy from the sun can be used to push a craft using a sail. It was very cool
 
GlasgowTitan said:
This is like a thing I saw on the Discovery channel a while back. It was a method of powering a space ship in space, it used (I think it was called) an Ion Drive. This was a tiny engine that on earth could barely power a car, but given time in space, with nothing to slow it, it would reach speeds closing on the speed of light.
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Quote taken from space.com

The ions travel out into space at 68,000 miles (109,430 kilometers) per hour, but Deep Space 1 doesnt move that fast in the other direction because it is much heavier than the ions. Its cruising speed is closer to 33,000 miles (53,100 kilometers) per hour.

The thrust itself is amazingly light -- about the force felt by a sheet of paper on the palm of your hand.

"If you want a mission in which you want to reach your destination in a hurry or accelerate quickly, ion propulsion's not for you," Rayman said. "It takes four days to go from zero to 60 (miles per hour). I like to say it's acceleration with patience."

But once ion propulsion gets going, nothing compares to its acceleration. Over the long haul, it can deliver 10 times as much thrust-per-pound of fuel as more traditional rockets. Each day the thrust adds 15 to 20 miles (25 to 32 kilometers) per hour to the spacecraft's speed. By the end of Deep Space 1's mission, the ion engine will have changed its speed by 6,800 miles (11,000 kilometers) per hour.
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Wow, 0-60 in 4 days, that's faster than my wifes A150 :D
 
Stonedofmoo said:
How much of a factor would gravity be though assuming the ground was perfectly level the whole distance
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Well friction is worked out from gravity.

Friction = Mu x Normal Reaction, where Mu is the frictional constant.

You work out the Normal Reaction from,

Normal Reaction = Mass x Gravity.

Thus its accually gravity that can change the amount of friction a car has.

The end formulae is,

Friction = Mu x ( Mass x Gravity )
 
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