Physics question

**cheesemethod** · 31st August 2009, 20:37

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?

**steve_t** · 31st August 2009, 20:57

Pretty sure it's a no. The power of the car has only to overcome the resistance afforded by the air and the tyres. If the added weight created more drag on the tyres then yes.

**Mully** · 31st August 2009, 21:04

But doesn't the extra weight affect the effect of gravity on the car?

**R6_kid:Me** · 31st August 2009, 21:09

Originally Posted by steve_t

Pretty sure it's a no. The power of the car has only to overcome the resistance afforded by the air and the tyres. If the added weight created more drag on the tyres then yes.

This would be my guess too. For an aircraft it would not be able to reach the same speed in straight and level flight as it needs to generate more lift to overcome the extra weight - same idea with a the car - more weight = more surface area and more pressure on the tyres = more resisitance to overcome.

**LBD** · 31st August 2009, 21:11

Originally Posted by Mully

But doesn't the extra weight affect the effect of gravity on the car?

Identical everything he said, I would assume that includes rolling resistance. When he says weight he probably means mass...so if both options have the same rolling and wind resistance, then there would be no difference in speed

**el_scor_cho** · 31st August 2009, 21:12

gunna go with a no also. but i think in your eg the car with the weight wont reach the same top speed as the one without.
i think the space question depends entirely on aerodynamics restricting the two objects when they reach max v

**nothingflash** · 31st August 2009, 21:19

Perhaps - I reckon the impact of added weight will affect acceleration more than top speed. Of course if you chucked them both out the side of a plane the heavier car will get there first.

**Big Dave** · 31st August 2009, 21:21

Theoretical extra Mass doesn't limit maximum velocity but requires greater force - or more time - to achieve it - and to stop it.

Real world and it all runs out of puff. Friction in supporting the weight etc.

**Big Dave** · 31st August 2009, 21:22

Originally Posted by nothingflash

Of course if you chucked them both out the side of a plane the heavier car will get there first.

Galileo proved otherwise.

**KiwiGs** · 31st August 2009, 21:25

Weight makes little difference to terminal velocity, it just takes a longer distance to achieve top speed for a heavier vehicle with the same power.

**steve_t** · 31st August 2009, 21:25

Originally Posted by nothingflash

Perhaps - I reckon the impact of added weight will affect acceleration more than top speed. Of course if you chucked them both out the side of a plane the heavier car will get there first.

Get a 50kg chick and a 120kg dude to go skydiving. Get the chick to powerdive and the guy to adopt the normal skydiving 'sprawl' (I have no idea what it's called). I guarantee you that the less-than-half weight wee girl will get to the ground faster

**nothingflash** · 31st August 2009, 21:27

Originally Posted by Big Dave

Galileo proved otherwise.

So if I throw a feather and a 1988 Mazda 323 S/W (with one careful owner) out of a plane the Mazda won't win?

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

**CookMySock** · 31st August 2009, 21:27

No.

There are two forces, one accelerating the object, and the other is the friction force of it moving through the atmosphere.

Assuming the force accelerating the object is constant, as speed increases friction force also increases until the two reach a zero algebraic sum. Accelleration ceases - the object reaches equilibrium - two constant but opposite forces..

Steve

**ducatilover** · 31st August 2009, 21:28

Originally Posted by Big Dave

Galileo proved otherwise.

I think I learned that during my kindy and nappies times

**ducatilover** · 31st August 2009, 21:31

Originally Posted by nothingflash

So if I throw a feather and a 1988 Mazda 323 S/W (with one careful owner) out of a plane the Mazda won't win?

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

We are talking about objects with the same co efficient of drag here...not jappa cars and dead chicken bits