Physics question

**p.dath** · 31st August 2009, 22:23

Consider this extreme case. You reach escape velocity. You are now in outer space. Gravity is now zero. There is no longer any gravitational acceerlation acting on you from earth. The reduction in the gravitational acceleration you experience decreases as you get higher.

The gravitational acceleration you experience while approaching your terminal velocity (assuming you are heading "up") has the same issue. The higher you get, the less of it there is.

**steve_t** · 31st August 2009, 22:27

Originally Posted by Metalor

I won't affect the top speed, but will effect the acceleration.

Those comments about a feather vs. a car falling from a great height:

The only reason the feather falls much slower is because the surface area to weight is much, much larger, so it feels more force (due to friction moving through air) PER unit of mass. If the went to the moon and did the same thing we would see the feather and the car reach the ground at the exact same time (provided the were dropped from the same height.)

Aren't u studying Physics Metalor?

**mossy1200** · 31st August 2009, 22:33

Originally Posted by LBD

Back to the original question.... acceleration is not in question...maximum speeds of the two cars is the question. The both will be the same, if power to propel, rolling and wind resistance are the same....mass (weight he said) will make no difference.

Originally talking of 100kg in boot it may be possible the weighed car may go faster because the extra weight on the driven wheels(assuming rear wheel drive)will provide less wheel slip therefore the same wheel speed will provide faster true travel speed.
Just thought I would spanner in the works.
Also assume the tyres have increased inflation in weighed car to offset increased drag on tyre to road.

**Big Dave** · 31st August 2009, 22:34

Originally Posted by p.dath

So I guess if you want the terminal velocity going "up or down" you need to consider that acceleration of the falling/rising body will vary.

If you consider the object to be "flying" horizontally then vertical acceleration will remain constant at 9.8 m/s/s, but because it is moving horizontal the vertical acceleration of gravity wont have a bearing.

And back on the flats (well, slightly rounds) did we consider that the vehicles weight decreases as the velocity increases.

If you go fast enough horizontally you'll eventually leave the planet and fly off into space. Some people see this as a goal.

**Big Dave** · 31st August 2009, 22:35

Originally Posted by Virago

Yeah, but where exactly is the seal? And wouldn't he prefer fish?

Arf arf arf. I did spot that and correct on second read - bit fishy though.

**p.dath** · 31st August 2009, 22:36

Originally Posted by mossy1200

Originally talking of 100kg in boot it may be possible the weighed car may go faster because the extra weight on the driven wheels(assuming rear wheel drive)will provide less wheel slip therefore the same wheel speed will provide faster true travel speed.
Just thought I would spanner in the works.
Also assume the tyres have increased inflation in weighed car to offset increased drag on tyre to road.

Haha. I love your thinking!

It might affect initial acceleration and velocity, but hopefully the wheels would achieve the same level of traction over the time it tacks to reach their respective terminal velocities.

But then again, if the heavier car runs out of fuel quicker ...

**Metalor** · 31st August 2009, 22:37

Yup.

Was just reading a comment on terminal velocity.

Terminal velocity is maximum velocity falling under the force of gravity where the object is no longer accelerating due to frictional forces from the air equaling the downward force of gravity but in the opposite direction.

p.dath was right when he said the car with the extra mass in it would have a higer terminal velocity. IF the added mass was 100kg, this translates to a downwards WEIGHT force of 9800 Newtons, so with the same cross-sectional area the heavier car would have to be falling faster in order for the frictional force from the air to equal(and opposite) that of the extra weight.

Sorry, hard to explain without diagrams.

**Big Dave** · 31st August 2009, 22:38

Originally Posted by mossy1200

Originally talking of 100kg

It was probably drugs too.

**Big Dave** · 31st August 2009, 22:38

Originally Posted by Metalor

Sorry, hard to explain without diagrams.

I posted link to NASA's - #39

**mossy1200** · 31st August 2009, 22:39

Originally Posted by p.dath

Haha. I love your thinking!

It might affect initial acceleration and velocity, but hopefully the wheels would achieve the same level of traction over the time it tacks to reach their respective terminal velocities.

But then again, if the heavier car runs out of fuel quicker ...

Which car is the STIG in again???My monies on Stig and you can have Jeremy Clarkson......