Physics question

[Big Dave]

EDIT: Depends from what height I suppose - anyway...

Missed this one - i think yes correct - and no - it depends what set of circumstances we are making up here.

If the height is lower than it takes for the objects to approach terminal velocity then they accelerate and impact at the same time.

If they reach respective terminal velocity then the heavier one pushes through the wind resistance better and accelerates longer

If we are talking pure theory and the wind and the atmosphere don't exist - they hit at the same time regardless of mass.

[Big Dave]

Yup.


Was just reading a comment on terminal velocity.

How do you calculate how the rate of acceleration slows as terminal velocity is approached?

[bogan]

Does anybody remember that thing in high school called physics? Perhaps you can help me then.

Does adding weight effect the maximum velocity of a self propelled body in atmosphere?

Imagine it this way. You have two identical cars, side by side on a flat straight piece of road. The cars have identical shapes, identical power, identical everything. Now place a 100kg weight into the boot of one of the cars. Obviously once they set off, the car with no weight in the boot will accelerate faster. But, will this 100kg extra have an effect on the top speed of the weighted car - will it be able to achieve the same top speed?

hmmm, hundy kg weight in the boot and questions about speeding cars. You arent planning to dispose of a body or two are ya?

If we consider the rolling friction to be independant of the cars weight, the qustion becomes, will adding 100kg to the boot of a car affect its aerodynamics? Depending on the car it could, the load on the rear springs will increase, and the load on the front will slightly decrease, changing the angle of the underside of the car relative to the road. It could possibly create a venturi effect furthur sucking the rear down, and create more turbulence at the rear, resulting in a lower pressure and less top speed.

[bogan]

How do you calculate how the rate of acceleration slows as terminal velocity is approached?

i guess itd be f=ma, where downward force=m*9.812 and upwards force is the result of wind friction, so a=net force/mass

[earl]

Well, when you have got this one sorted,perhaps you could answer the question posed by Lindburg when he was crossing the atlantic for the first time. Does a fly, flying in a flying aircraft add to the weight and therefore the fuel consumption?

[ducatilover]

Well, when you have got this one sorted,perhaps you could answer the question posed by Lindburg when he was crossing the atlantic for the first time. Does a fly, flying in a flying aircraft add to the weight and therefore the fuel consumption?

That is the ultimate question

[Big Dave]

That is the ultimate question

I would have gone for 'what is the meaning of life, the universe and everything'.

[Metalor]

Well, when you have got this one sorted,perhaps you could answer the question posed by Lindburg when he was crossing the atlantic for the first time. Does a fly, flying in a flying aircraft add to the weight and therefore the fuel consumption?

Yes, because the flys wings are displacing the air in the plane, creating a lifting force on the fly's wings, but the wings are providing a downwards force on the air (pressure down). This downwards pressure would translate to pressure on the floor of the plane. You can imagine this more easily say if a giant bird flew past above the plane, and as it beat is wings down, creating lift for the bird, that pressure from the air would push the plane down.

Haha, it's a pretty clever question though. Ultimately the mass and effect of the fly to the plane is completely negligible.

[Hans]

The engine needs to carry out more work to propel the heavier car at the same speed. All other things being equal, the heavier car will have a lower top speed.

[scracha]

When determinining top speed of a car, the most important one is air resistance (drag). This force is proportional to the square of the velocity so it's numero unu. That's why at very high speeds, you need massive amounts of extra bhp even to gain an extra 1kmph.

Fair is force of air resistance
Cair is the co-efficient of air friction for a given vehicle
v is the vehicles velocity

Fair = -Cair * v^2

There "driving" force in the car is Fgrip (force from the tyres which generally spin from the engine). There's also Fres (force from rolling resistance). Fres is directly proportional to the velocity and in a car. As Fair is "squared" then it takes as the main friction force at roughly above 100Kmph.

F = Fgrip + Fres + Fair

Using Newton's law
a = F / M (accel = force over mass)

You then integrate the accelleration over time but essentially, higher accelleration, a higher top speed.

BUT, larger mass, lower top speed.
BUT BUT BUT
F is also affected by the larger mass as
Fgrip is increased (less slip)
Fres is increased
Fair - well without a wind tunnel, we don't know for sure, but assuming the weight is in the rear of the car we'd assume that Cair is increased as it's nose would be higher.

As Fair is "squared" then I reckon the heavier car would be slower if the weight is put in the boot but faster if the weight was placed further forward. A lot depends on the aerodynamics of the car and also whether we're talking about an 850cc engine or an 8 litre engine. We've also assumed the road is flat.

Fuck..I dunno...my head hurts now.

[MisterD]

The engine needs to carry out more work to propel the heavier car at the same speed. All other things being equal, the heavier car will have a lower top speed.

Newton's first law: in the absence of a net external force a body either remains at rest or moves with constant velocity.

The initial assumptions were that the extra mass of the second car didn't increase the friction / rolling resistance therefore the only two forces to consider are a) the motive force of the engine and b) air resistance. These are equal for both cases therefore the maximum velocity of the cars is the same.

[rickstv]

Oh Bugger this for a laugh, you guys are giving me a headache

[MattRSK]

v_term=(8ρ(density body) gr)/(3Dρ(density air) )


This is the formula for terminal speed in a fluid (ie. Air), As the density of the body is taken into account I would say the car with the greater mass will have a greater terminal speed.

[Hans]

Only if you drop it from a plane.

[steve_t]

I would have gone for 'what is the meaning of life, the universe and everything'.

42... man, I'm old