Driving a car on the roof of a truck.

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In summary, friends were discussing the question of how fast a car needs to be moving when on top of a truck to not fall off. The car needs to be parked as any velocity difference will cause it to fall off. The wind may also contribute to the car falling off, but it depends on the wind speed and car's aerodynamics. When driving on top of the truck, the car's speed will be cumulative with the truck's speed, but when changing the reference point to the ground, the car will only be going the speed of the truck plus its own speed.
  • #1
aLLie04
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With limited knowledge of physics, my friends and I have been discussing this question and cannot come to an agreement.

If a truck is driving on a highway (at 60 mph let's say), and a car is on top of the truck, how fast does the car need to be moving to not fall off the back or to drive off the front?
Does it need to be driving the speed of the truck? Or does it just need to be traveling fast enough to break through the wind (and how fast would this be)? Can it stay parked, or will it fall off?
 
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  • #2
aLLie04 said:
If a truck is driving on a highway (at 60 mph let's say), and a car is on top of the truck, how fast does the car need to be moving to not fall off the back or to drive off the front? Does it need to be driving the speed of the truck? Or does it just need to be traveling fast enough to break through the wind (and how fast would this be)? Can it stay parked, or will it fall off?
The car needs to be parked. It's speed relative to the truck is zero, otherwise if there's a difference in velocity, the car goes off the truck.
 
  • #3
So the wind doesn't have an effect on it when its parked?
 
  • #4
aLLie04 said:
So the wind doesn't have an effect on it when its parked?

Sure it does.
But if you have any relative velocity with respect to the truck, your car is eventually going to fall off.

Thus, you must hope that when standing still with respect to the truck, the friction between the car's tyres and the truck roof is sufficient to witstand the windy assault.
 
  • #5
If it were in neutral, and not tied down, it could conceivable be blown off of the back. In reality, anyone transporting a car uses restraints. Check out a car-hauler the next time you see one parked.
 
  • #6
If you were to be driving on top of the truck, would the speeds become cumulative? I mean, in reference to the ground would the car be going the speed of the truck plus its own speed? I understand that in reference to the truck it would only be going the speed the speedometer says, but what happens when you change the reference point to the ground?

Thanks.
 
  • #7
Thats what I was thinking, but in theory could you have the car sit there without blowing off the back while its parked (oppose to in neutral). In my mind it seems that the wind would eventually cause it to creep its way off the back because its not restrained by anything.
 
  • #8
That entirely depends upon the wind speed (assuming that the road isn't very bumpy) and the aerodynamics of the car. A good tornado can toss a car half a mile or more. It wouldn't likely happen under any normal driving conditions. A reasonably streamlined car sitting on a truck going 100 kph on a still day wouldn't likely notice at all.
 
  • #9
aLLie04 said:
If you were to be driving on top of the truck, would the speeds become cumulative? I mean, in reference to the ground would the car be going the speed of the truck plus its own speed? I understand that in reference to the truck it would only be going the speed the speedometer says, but what happens when you change the reference point to the ground?

Thanks.
Speeds are additive, just like your instincts tell you.
 

Related to Driving a car on the roof of a truck.

1. Can a car safely drive on the roof of a moving truck?

It is not safe to drive a car on the roof of a moving truck. This can be extremely dangerous for both the driver of the car and other vehicles on the road. It is important to follow all traffic laws and regulations to ensure the safety of everyone on the road.

2. What are the potential risks of driving a car on the roof of a truck?

The potential risks of driving a car on the roof of a truck include the car falling off and causing accidents, the car getting damaged or destroyed, and the driver losing control of the car. It can also create a distraction for other drivers on the road, leading to potential collisions.

3. Is it legal to drive a car on the roof of a truck?

No, it is not legal to drive a car on the roof of a truck. This is considered a traffic violation and can result in fines and penalties. It is important to follow all laws and regulations to ensure the safety of yourself and others on the road.

4. Can a car be securely attached to the roof of a truck?

While there are methods to attach a car to the roof of a truck, it is not recommended or safe to do so. The high speeds and movements of the truck can cause the car to become loose and potentially cause accidents. It is best to transport a car using a trailer or flatbed truck instead.

5. Are there any situations where driving a car on the roof of a truck would be appropriate?

No, there are no situations where driving a car on the roof of a truck would be considered appropriate. It is always safer to transport a car using a designated trailer or flatbed truck. Driving a car on the roof of a truck should be avoided at all costs.

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