Please explain this

[truckemup97]

You're the expert, of that I have no doubt. I'm not arguing with you, I'm just trying to understand. My physics classes were a long time ago and I've likely forgotten most of what I learned.

If I were standing in the back of the pickup and threw a rock, it would be going the speed of the pickup plus the speed of my arm at the time of release. Why would it be different if it were thrown (slung?) from the tread of a tire?

 

[handejector]

Y'all are leaving out centrifugal force.
I think rotational speed of the tire also comes into play, compounded somehow with the truck's speed, but I'm not learned enough to know how.

Let's face it though- if the rock was not moving faster than the truck, how did it get ahead of the truck?

 

[truckemup97]

Y'all are leaving out centrifugal force.
I think rotational speed of the tire also comes into play, compounded somehow with the truck's speed, but I'm not learned enough to know how.

Let's face it though- if the rock was not moving faster than the truck, how did it get ahead of the truck?

That's what I was trying to say. How is it that a gorilla can communicate more effectively than I?

 

[amazingflapjack]

How about a temp or pressure change. Was the A/C on? If it is more of a crack, I would look for something like that, or frame flex, or a combination of factors. Just tryin' to think outside the box. Flapjack.

 

[oldman45]

You're the expert, of that I have no doubt. I'm not arguing with you, I'm just trying to understand. My physics classes were a long time ago and I've likely forgotten most of what I learned.

If I were standing in the back of the pickup and threw a rock, it would be going the speed of the pickup plus the speed of my arm at the time of release. Why would it be different if it were thrown (slung?) from the tread of a tire?

No it would not. Your throw would have to be with such power that the rock speed would exceed the speed of the truck. A good ball pitcher can hit those speeds. Also you have drag on the rock from the wind. If you were inside the vehicle and it be possible to throw the rock, then the wind drag would not be as great.

Propulsion motion is constant. A rock slung from a tire is in constant motion with the tire. Then there is a force pushing it to a point of release but the force dies off with gravity. The same with a bullet. Unfired in a gun pointed the same way as the pickup motion, the bullet is travelling at the same speed as the truck. Given the ignition of the powder to propel the bullet, the bullet will exceed the speed of the truck but slow down with distance whereas the truck speed will remain constant.

Centrifugal force will initially propel an object at a higher rate of speed but it will bleed off speed rapidly once released from the powering force.

Now back to schools, I graduated with my engineering degree in 1967 or over 44 years ago. The mind dims with age.

 

[oldman45]

How about a temp or pressure change. Was the A/C on? If it is more of a crack, I would look for something like that, or frame flex, or a combination of factors. Just tryin' to think outside the box. Flapjack.

There is an actual peck in the cracks. Something hit the windshield twice. What the something is will likely remain a mystery.

 

[Gasman1972]

If you held a rock in your hand in the back of a truck at 60 mph, you and the rock would be going 60 mph. The moment you let go of the rock it instantly slows down because it has no driving force, just weight and gravity. If you throw it 30 mph the speed of the rock does not become 90 mph, it becomes 30 mph from the point you throw it. To a person standing on the road the rock would be going 90mph or a little less, but the rock and the truck zero out kind of, and at the moment you let the rock go the rock is going 30 and the truck is going 60.

 

[oldman45]

That's what I was trying to say. How is it that a gorilla can communicate more effectively than I?

The rock did not get in front of the truck. If we assume the rock was thrown from the tire treads as the rock was being brought down on the front side of the tire, then it would have hit the pavement, bounced up and while it is in a directional variance, it is slowing down while vehicle speed is constant. More than likely, a rock would have came loose to the rear and not to the front. Tread distortion happens when the tread is around the bottom of the tire. Rock dings are common to the rear of an inter fender, not the front.

 

[oldman45]

Y'all are leaving out centrifugal force.
I think rotational speed of the tire also comes into play, compounded somehow with the truck's speed, but I'm not learned enough to know how.

Let's face it though- if the rock was not moving faster than the truck, how did it get ahead of the truck?

Lee, how many times have you had a rock hit your windshield that was thrown by your own tires? It would have to go down to the pavement, then upward far and fast enough out in front of the truck to gain enough altitude to hit the windshield
and that is not going to happen. The vehicle would have ran over it. You hear this all the time when a rock lets go from tire treads. The rock hits the undercarriage.

Have you ever seen a rock being thrown to the front of a vehicle?

 

[VM]

...............While a rock thrown by a tire would be doing the same speed .............

I'm not a Mathematician, but I did stay at Holiday inn Express recently.
I don't buy your theory of the rock being thrown at same speed as vehicle speed.
Wheels/tires spin on spindle or axle and are measured by revolutions per minute.
The smaller the tire's diameter, the faster it will spin.
Say a vehicle is pulling a trailer behind it with little, tiny, wheels on it. These tiny wheels could potentially be spinning twice the speed of your tow vehicle's tires.
Both the car and trailer are doing 70 MPH - your theory says that rocks thrown from either tire will travel at same speed........NOT!
Also, I've been telling my wife for 30 years to quit following (tailgating) Big Trucks so close because they throw rocks BEHIND them (into her windshield) - I've never seen a tire throw a rock forward.
Finally, I'm sticking to my Bigfoot/Slingshot previous answer.

 

[old bear]

Probably caused by an under powered class 1 Phaser.... or not

"There hear" Rod Sterling.

 

[DeathGrip]

Acorn tossing evil tree rats.

 

[ditrina]

I'm not a Mathematician, but I did stay at Holiday inn Express recently.
I don't buy your theory of the rock being thrown at same speed as vehicle speed.
Wheels/tires spin on spindle or axle and are measured by revolutions per minute.
The smaller the tire's diameter, the faster it will spin.
Say a vehicle is pulling a trailer behind it with little, tiny, wheels on it. These tiny wheels could potentially be spinning twice the speed of your tow vehicle's tires.
Both the car and trailer are doing 70 MPH - your theory says that rocks thrown from either tire will travel at same speed........NOT!
Also, I've been telling my wife for 30 years to quit following (tailgating) Big Trucks so close because they throw rocks BEHIND them (into her windshield) - I've never seen a tire throw a rock forward.
Finally, I'm sticking to my Bigfoot/Slingshot previous answer.

Well that explains it.. of course if you really want to prove it..Then the following must be true...

which simplifies to

If one adds

times this to the EFE, one gets the following equivalent "trace-reversed" form

Reversing the trace again would restore the original EFE. The trace-reversed wheel spinning, with the rock actually peircing the wind shield..

 

[oldman45]

Well that explains it.. of course if you really want to prove it..Then the following must be true...

which simplifies to

If one adds

times this to the EFE, one gets the following equivalent "trace-reversed" form

Reversing the trace again would restore the original EFE. The trace-reversed wheel spinning, with the rock actually peircing the wind shield..

And anyone driving down a gravel road would have a busted windshield.

 

[Sprefix]

For sure........

Well that explains it.. of course if you really want to prove it..Then the following must be true...

which simplifies to

If one adds

times this to the EFE, one gets the following equivalent "trace-reversed" form

Reversing the trace again would restore the original EFE. The trace-reversed wheel spinning, with the rock actually peircing the wind shield..

Yep, what he said..............

 

[handejector]

Whur's all ire rock-it siyuntissts and fisisisstes when we need 'em?

Lee, how many times have you had a rock hit your windshield that was thrown by your own tires?

Never.

Have you ever seen a rock being thrown to the front of a vehicle?

Yes. I was in it.

 

[venomballistics]

rock from the tread ... OK Ill buy that once on the basis that one in a million shots do happen ... but twice?
Nah buddy, its something else

 

[Beejabbers]

Well that explains it.. of course if you really want to prove it..Then the following must be true...

which simplifies to

If one adds

times this to the EFE, one gets the following equivalent "trace-reversed" form

Reversing the trace again would restore the original EFE. The trace-reversed wheel spinning, with the rock actually peircing the wind shield..

That's easy for you to say!

 

[StuperDan]

Once, while traveling with my wife on a two lane highway with no other cars in sight, we heard a very loud pop. This pop was so loud that I initially seriously thought someone shot the car. After leaving the area, I pulled over. No one around for miles. On the windshield directly in front of my wife's face was a blackend blast mark. Like you might expect to see if you threw a small firecracker at a window. It wiped off clean with my finger leaving a very small etch in the glass. Not even a crack. Just a dust sized white speck. I was stumped. Anything big enough to make the much noise and leave a carbon ring smudge should have put at least a good sized chip in the windshield.

Later that evening, watching the news, they mentioned the earth was moving through a debris cloud and that for the next few days there would be pretty meteor showers at night.

I could only conclude that a very small very fast and hot flecked of space rock hit us. Either that or there are squirrels or birds armed with firecrackers in Montana.

 

[310Pilot]

What was the weather when your windshield was hit? If there were any thunderstorms in the vicinity (even up to 20 miles away), it could have been hail stones. Severe thunderstorms will sometimes "throw" hail many miles from their location - that's one of the reasons (in addition to staying out of airframe-destroying severe turbulence) that we always fly at least 20 miles from strong thunderbumpers. Hail usually is ejected out of the anvil side of the T-storm, which is why one never wants to fly under, or near, the anvil. Just a possibility, and the small impacts with cracks spreading from them sounds just like hail damage to a windshield (we had a pretty good hail storm a few weeks ago, and I have replaced one windshield, need to get a second replaced, as well - one car hit while driving, the other just sitting).

 

[oldman45]

What was the weather when your windshield was hit? If there were any thunderstorms in the vicinity (even up to 20 miles away), it could have been hail stones. Severe thunderstorms will sometimes "throw" hail many miles from their location - that's one of the reasons (in addition to staying out of airframe-destroying severe turbulence) that we always fly at least 20 miles from strong thunderbumpers. Hail usually is ejected out of the anvil side of the T-storm, which is why one never wants to fly under, or near, the anvil. Just a possibility, and the small impacts with cracks spreading from them sounds just like hail damage to a windshield (we had a pretty good hail storm a few weeks ago, and I have replaced one windshield, need to get a second replaced, as well - one car hit while driving, the other just sitting).

That is possible. While there were not any thunderstorms in the area, there was some unsettled weather on the leading edge of a cold front.

Now we can rule out rocks from my own vehicle. It is not going to be possible. For all the forumla using people, there are missing pieces of needed information such as the weight of the projectiles and the shape. Also being on a concrete roadway and having two hits to the windshield would defy all odds.

Many years ago, mostlikely still mentioned on the internset, a commercial pilot was flying at several thousand feet above ground. Suddenly, the plane's windshield was struck by a large snake. How did the snake get up there? It was suggested a bird dropped it as the plane got too close. Why would a bird be at that altitude and why would a bird have a large snake in it's grasp?

Things happen that cannot be explained.

 

[JohnnieB]

Hopefully someone armed with a calculator reviews traffic safety reports because 70mph = 102.6667fps rather than 105fps.

Nitpicking aside, the tread on top of a tire moves forward at the same speed as the tread on the bottom of the tire moves backwards.
Unless the tire is spinning or sliding, the speed the tread on the bottom is moving backwards equals the vehicle's velocity.
Therefore the relative speed between the tread on the bottom of the tire and the road is -Zero- while the relative speed of the tread on top of the tire is twice the vehicle's velocity.

Ergo, a projectile launched forward from the top of the tire will be traveling at twice the vehicle's velocity at the moment of departure.
From that point on it follows a path dictated by gravity, aerodynamics and any barriers obstructing its ballistic arc.

Bottom line:
Can a stone be thrown off a front tire, hit the road, bounce up and be hit by the vehicle's windshield? Yes!
Is it likely to happen? It depends on wheelwell design, ground clearance, road surface and other factors, but to have it happen twice in a few miles would most likely be unlikely.

If it ever happens to me, I'll buy a lottery ticket since I just used up all my bad luck for the day.

 

[Babalooie]

Cosmic debris, no doubt about it.

 

[ohiobuckeye]

You're the expert, of that I have no doubt. I'm not arguing with you, I'm just trying to understand. My physics classes were a long time ago and I've likely forgotten most of what I learned.

If I were standing in the back of the pickup and threw a rock, it would be going the speed of the pickup plus the speed of my arm at the time of release. Why would it be different if it were thrown (slung?) from the tread of a tire?

Brings to mind a question sometimes debated....If you are traveling at the speed of light and turn on the headlights, would they light the path ahead of you?...

 

[DeadAye]

Brings to mind a question sometimes debated....If you are traveling at the speed of light and turn on the headlights, would they light the path ahead of you?...

If you're on a path you already have more problems than figuring that out presents
Write this down:
ONLY go the speed of light out in space!

I'm going to go with the space junk scenario.
That or meteorites.
Once - Maybe some nut shooting at cars, but twice, miles apart........... Ya got a lot of nuts that don't like cops out your way?

 

[roscoguy]

... the tire is moving at 70 mph or 105 feet per second. Anything coming off the tire will travel the same speed.

Something about this bothered me & stuck in my little brain... The thing is: something falling from the tire would be going 70mph, but something thrown by centripetal force from an object will have it's own initial velocity +/- the velocity of the throwing object - depending on their relative directions. A month or 2 ago there was a really good show about light (starring Neil Degrasse Tyson, IIRC) that explained that light was the only exception to this & actually even gave examples wherein somebody threw an object forward or reverse from a moving vehicle. Light travels at the same speed regardless of the velocity of whatever it emanated from. (So the answer to ohiobuckeye's question would be "No. You'd just have to drive very carefully! )
I know this is kind of counter-intuitive but Neil has never lied to me before... Another proof if this: look inside your wheel-wells after driving on a wet/muddy road. There will be water/mud splatter all around the tire - not just behind it. So it is possible for a rock to briefly travel faster that your vehicle. Then it would just have to be thrown at the correct angle to bounce up to the same height as your windshield. At that point, it could actually stop (relative to the road) & you'd still hit it @ 70mph. It seems unlikely that a car would have either the ground clearance or enough room in the wheel-well for this to happen, but looking at a pickup, I believe that it could (but rarely would).
Edit: I should have read all of the posts added while I was wasting my morning thinking about this. Then I could have just given JohnnieB a +1.

 

[Aubie]

Well, tires do throw rocks forward. Appears most of you have never ridden a motorcycle. I have and my windshield has been hit several times and so have I over the years while riding bikes.

Therefore it is possible your tire could have picked up a small rock, threw it forward and it bounced up and you ran into it.

 

[truckemup97]

Brings to mind a question sometimes debated....If you are traveling at the speed of light and turn on the headlights, would they light the path ahead of you?...

You try it first and let me know.

 

[nicky4968]

Growing up surrounded by gravel roads, I can tell you that rocks do go forward, bounce, and you run into them. Most of them don't clear the bumper. Usually not large rocks, but small ones without much mass. I don't believe the rock is "thrown" from the tread, however. They best I can do is offer the analogy of a watermelon seed being squeezed between your finger and thumb.

 

[oldman45]

Well, tires do throw rocks forward. Appears most of you have never ridden a motorcycle. I have and my windshield has been hit several times and so have I over the years while riding bikes.

Therefore it is possible your tire could have picked up a small rock, threw it forward and it bounced up and you ran into it.

Nope, not possible. Even if the premise that a rock was tossed forward and at a faster rate than the truck is moving, it would had to have gone over six feet high after clearing over five foot of hood. I drive a large one ton dually that is set up to hold all the cameras, measuring equipment, cones, computers and machinery needed at a accident or crime site. It has large tires so I can get across medians, curbs and such. The windshield is about six foot off the ground where the items hit. With about 400,000 miles on it, not even a headlight or lens cover has been broken by a rock.