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post #31 of 36 (permalink) Old 31-05-19, 10:04 PM
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Sorry that is wrong - my last engineering physics lecture was many years ago but I don't think the laws of conservation of momentum have changed since graduation.

The lighter vehicle experiences higher acceleration and therefore must experience higher forces (unless mass is converted)

Go back and read the answers given in your link.

https://www.physicsclassroom.com/cla...tion-Principle

Once again you misjudge the TOTALITY of `force absorption` as it applies to a vehicular accident: The statement above applies implicitly if the force of impact is constant, but in a car with crumple zones and other `defensive` measures the FORCE is Mass x Acceleration.
A car that is lighter has lower MASS, I think we can all accept that? The protective measures extend the absorption of that force over a greater TIME actually has lower momentum. Force = Mass x Acceleration - when both Mass and Acceleration is LOWER (Acceleration is a `consequent`force Average acceleration = change in velocity (Δv) divided by the time interval of the velocity change (Δt), or a = Δv Δt. INCREASE rate of deceleration and both parts contribute to a lower FORCE vector.)

Your `Momentum argument` fails to consider the basic principles involved and thus erroneous in this discussion... Are you misconstruing `Acceleration` with `Speed` perhaps?
Not going to go into a dissertation on physics but you may want to touch up on some of yours.

Look up conservation of momentum and apply it to each vehicle.

The lighter vehicle experiences a higher acceleration in the collision. And since the occupants are in the same reference frame, they also experience the same acceleration.

If I am misunderstanding momentum, please explain it in terms a senior engineer can understand.
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post #32 of 36 (permalink) Old 04-06-19, 01:14 PM
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https://www.bbc.co.uk/news/uk-england-sussex-48514448

Then explain that..?

The heavy pick up truck leads to the death of both driver and passenger, yet the mighty 1,200 kilo Mini only injures..?
Are you suggesting the 2-tonne pick up truck and its passengers defied the laws of physics?

Momentum doesn't kill anyone. Impact and acceleration does.
F=ma tells all of us that if Mass is less and the acceleration the same, resulting forces are also less...

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post #33 of 36 (permalink) Old 04-06-19, 05:27 PM
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Originally Posted by SEvans View Post
https://www.bbc.co.uk/news/uk-england-sussex-48514448

Then explain that..?

The heavy pick up truck leads to the death of both driver and passenger, yet the mighty 1,200 kilo Mini only injures..?
Are you suggesting the 2-tonne pick up truck and its passengers defied the laws of physics?

Momentum doesn't kill anyone. Impact and acceleration does.
F=ma tells all of us that if Mass is less and the acceleration the same, resulting forces are also less...
What a crock!

Where does the a come from? Impulse. And what is impulse? Momentum change.

Momentum is the fundamental descriptor of the situation and it is augmented with time.

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post #34 of 36 (permalink) Old 04-06-19, 08:46 PM
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Originally Posted by SEvans View Post
https://www.bbc.co.uk/news/uk-england-sussex-48514448

Then explain that..?

The heavy pick up truck leads to the death of both driver and passenger, yet the mighty 1,200 kilo Mini only injures..?
Are you suggesting the 2-tonne pick up truck and its passengers defied the laws of physics?

Momentum doesn't kill anyone. Impact and acceleration does.
F=ma tells all of us that if Mass is less and the acceleration the same, resulting forces are also less...
Ford ranger: ~4000 lbs
Convertible Mini: ~2700 lbs
Using non-standard units for ease the momentum of each:
p = m*v (momentum = mass * velocity)
p(Ford) = 4000 * 60 = 240,000
p(mini) = 2700 * 112 = 302,400
p(Ford) << p(mini) therefore the truck was pushed backward (extreme acceleration) and it's occupants experience that same acceleration and were killed.

Now that is an over simplification because they are two different vehicle classes and trucks have much lower safety standards.

But physics still won - the vehicle with the higher momentum experienced a lower, survivable acceleration.
In an accident where the speeds were similar the heaviest vehicle wins the momentum argument.
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post #35 of 36 (permalink) Old 05-06-19, 01:27 AM
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Take it to extremes. If the higher mass were to experience the greater force, can you imagine someone about to jump from a bridge.

The police would be shouting "don't jump, the poor people on earth will be badly injured". &#x1f923;&#x1f923;&#x1f923;
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post #36 of 36 (permalink) Old 06-06-19, 01:39 AM
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Originally Posted by SEvans View Post
https://www.bbc.co.uk/news/uk-england-sussex-48514448

Then explain that..?

The heavy pick up truck leads to the death of both driver and passenger, yet the mighty 1,200 kilo Mini only injures..?
Are you suggesting the 2-tonne pick up truck and its passengers defied the laws of physics?

Momentum doesn't kill anyone. Impact and acceleration does.
F=ma tells all of us that if Mass is less and the acceleration the same, resulting forces are also less...
Your deduction is based on false assumption that acceleration is same for both objects involved in a crash. This is nonsense. Third law of motion tells us that the forces acting on both objects are equal and have opposite directions. With equal forces acceleration is inversely proportional to mass of a car.
Imagine the Mini crashing head on with a freight train. How do you figure this out?
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