New Speeding shock Ad (Physics people in here please)

Zip

Zip

Zip

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This is a newish ad, In my state its been on since the start of the year but its been around a bit longer in Victoria.

Anyway my Girlfriend said that her physics class and there teacher worked out that what is said in the ad about cutting down 5kph and saving the girls life by reducing the impact by cutting how quick the car slows is wrong.

Here is the ad.

http://www.mac.sa.gov.au/popup/tv_campaign.php?id=38


So will cutting back from 65kph to 60kph really reduce the end hitting speed by as much as he said?

I have in my mind of how it could, and thats down to reaction time and what not that my girlfriends class might have forgotten about.

Anyway, Have a look and work out how accurate it is:D
 
The problem is the stats are a load of old rubbish, because accidents don't happen at free travelling speed, so you need to take the cars braking performance into account to work out the impact speed if you're doing it properly, which the stats this ads are based on don't do.
 
2mph is the difference between a bruised leg and major trauma and being thrown 6 metres? :confused:

Zip said:
Anyway my Girlfriend said that her physics class and there teacher worked out that what is said in the ad about cutting down 5kph and saving the girls life by reducing the impact by cutting how quick the car slows is wrong.
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Well what is their reasoning?
 
Gilly said:
Well what is their reasoning?
Click to expand...

Im not sure what there reasoning is:confused:

She just said they had worked it out and it was wrong. She doesnt like looking at other views once her minds made up:p

Anychance that the Reaction time could come into play? By the time the driver sees her at either speed he has driven that little bit more before he hits the breaks to slow him self down?
 
Of course it will come into play.

Reaction time, braking distance of the car, performance of the brakes, degredation of the brake discs/pads, condition of the tyres, type of tyres, condition of the road, road surface type, weather, panic and skill of the driver... It all comes into play.

That is why the ad is bunk. That is also why I asked what their reasoning is.

Getting people to be aware of their speed through built-up areas is still no bad thing though.
 
I assume though that performance of the brakes, degradation of the brake discs/pads, conditions of the tyres, type of tyres, condition of the road, road surface type, weather and skill of the driver are all constant though, all thats being changed is the initial speed of the car. Still think it seems very far fetched though!
 
as mentioned its an incredibly complicated thing to work out as your not talking about a constant, or even smooth curve of deceleration for a car hitting the brakes in an emergency stop, hell in the advert he even locks the wheels up...

but lets give it a theoretical go:

The 5kph would effect the reaction distance by an amount, imagine your reaction time is about 1.5seconds... traveling at 65kph that would be ~27meters (65000meters ph / 3600s = 18.05 meters per second *1.5)
where as 60kph would be 25meters...

I'll use this stopping distance calculator for ease... We can see it would take 45.88m to stop from 60 and 53.84 from 65 (plus the reaction time...)

we can work out the distance from the driver to the pedestrian at the driver sees them by saying: distance=(reaction distance + stopping distance) - stopping distance at 32mph (assuming the impact has negliable effect on the speed)
so @ 65kph:
distance = (27+54)-13 = ~68m between the driver and the pedestrian...

so if we plug that into the 60kpm distance from the impact we'd stop (x)

68m = (27+46)-x or 68-(27+46)=x =5

again using my the funkey calculator a stopping distance of 5meters would give a car traveling at about 19kph at point of impact....

so i call BS on the add ;-)
 
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Well looking at siliconslaves dabblings with math there you have to ask why a pedestrian would be shuffling aimlessly across a road and the driver thinks an accident is going to happen at a distance of 53 meters.

53 meters is pretty far away.
 
DiG said:
I assume though that performance of the brakes, degradation of the brake discs/pads, conditions of the tyres, type of tyres, condition of the road, road surface type, weather and skill of the driver are all constant though, all thats being changed is the initial speed of the car.
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So? They're applying this to every car on every road, are they not?
 
You have to remember the equation for kinetic energy. roughly the energy in a collision is equivalent to the square of the speed. So say for 60mph crash the energy involved is 3600. If you now increase the speed to 65mph then the energy is 4225. This is a bit less then a 20% increase in energy for a 5mph increase in speed. This is all very simplistic but it shows the idea behind it. This increase in energy has to be transferred somewhere and the brakes can only absorb so much.
 
Blinkz said:
You have to remember the equation for kinetic energy. roughly the energy in a collision is equivalent to the square of the speed. So say for 60mph crash the energy involved is 3600. If you now increase the speed to 65mph then the energy is 4225. This is a bit less then a 20% increase in energy for a 5mph increase in speed. This is all very simplistic but it shows the idea behind it. This increase in energy has to be transferred somewhere and the brakes can only absorb so much.
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That's more than twice the speed difference they're talking though :)
 
I don't see how 5kph (which is what 2 or 3 mph?) is going to make any measurable difference in someone's injuries. They're still going to be in hospital for several months if a car hits them at that speed, or worse.

That advert is still crap eitherway. It's basically saying "if you are travelling at 60 and hit someone with a bit of emergency braking before thrown in, then there's a good chance they will simply stand up, shake hands and walk off."

Pretty funny that as soon as that car hits the person it comes to a stop immediately :) So it had already burnt off 99% of its kinetic energy at the point of impact... which is why the person could stand up. A more realistic video would have seen the car continue travelling probably at least another 10-15 meters from the point of impact. With the person going over the top of the car or off to one side... it's not always the initial impact that kills someone, it's the fall that does serious damage too... imagine getting tossed up in the air and thinking "ouch that kinda hurt but I should be OK if I land on the grass" and then hitting your head on a kerb?
 
NathanE said:
I don't see how 5kph (which is what 2 or 3 mph?) is going to make any measurable difference in someone's injuries. They're still going to be in hospital for several months if a car hits them at that speed, or worse.
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I suppose what it's saying is that slowing down by 5kph allowed the driver too see her sooner, apply the brakes earlier, and the car has less speed to shed after applying the brakes. All those things added together means the car impacted her at a much slower speed than before, not just 5kph slower.

Load of arse though, he wouldn't have hit the bint atall if she didn't step into the road without looking.......
 
Hitting someone when going slower will cause less injuries. FACT
There's no point saying "the speed difference is not gonna affect it much" as if it's a way to justify that you break the speed limit sometime.

However, the ad is simplifying to much though. And what modern car with ABS would skid like that?

DreXeL said:
I suppose what it's saying is that slowing down by 5kph allowed the driver too see her sooner, apply the brakes earlier, and the car has less speed to shed after applying the brakes. All those things added together means the car impacted her at a much slower speed than before, not just 5kph slower.
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I see. I think you're right there actually
 
Seems pretty obvious that you're more likely so skid at speed in to a person if you brake hard at a higher speed, whereas a slower speed will allow you to brake just as hard but it'll be controlled and as a result brake faster.
 
Hen_Dawg said:
Hitting someone when going slower will cause less injuries. FACT
There's no point saying "the speed difference is not gonna affect it much" as if it's a way to justify that you break the speed limit sometime.

However, the ad is simplifying to much though. And what modern car with ABS would skid like that?


I see. I think you're right there actually
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Yes I agree however why fund the creation of an advert which probably cost the AU tax payers a couple hundred grand when the advert has a crap plot? They could have just made it more realistic instead of trying to say that 5kph makes the difference between being in hospital for months versus just standing up and walking off without so much as a lawsuit ;)

Just seems a wasted opportunity IMO. There's so many good adverts of this style that could be made they just always seem to be scripted by do-gooder idiots who don't even have the slightest understanding of physics.
 
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