Once and for all!

[fireman57]

Re: Once and for all!

I'm watching mine grow while wasting time reading this instead. Much more gratifying.

 

[jtexas]

Re: Once and for all!

At the moment of impact, both cars are stopped (assuming they the weigh the same). A brick sitting on the front bumper of car A will impact the grill of car B at the speed which car A was traveling. This is the same speed (and same force) with which it would impact the brick wall. Assuming of course that the brick wall actually stops the car.<br /><br />That means that the two-car crash is twice the force, but the effect on each car is the same as if it hit a brick wall. <br /><br />But, it's worse than if it hit a Mazda Miata, or a slower-moving car, because then it wouldn't get stopped cold. right?<br /><br />But if it hits a bus which knocks it backwards, it's just that much worse.

 

[Ralph 123]

Re: Once and for all!

Newton's third law of motion states for every action, there is an equal and opposite reaction.<br /><br />When a car hits a wall going 50 mph, the wall feels the force and so does the car. They feel the same force<br /><br />When the wall moves toward the car at 50 mph (i.e., becomes another car), they both feel the force of 100 but in opposite directions. That is, they feel the force they exerted plus the force the other object exerted.

 

[snapperbait]

Re: Once and for all!

Yea, but I bet two cars crashing into each other makes a bunch more noise than one crashing into a wall... <br /><br /> KABOOOM squared; or somethin'....<br /><br />I got weeds that need pullin', but it's dark..

 

[brother chris]

Re: Once and for all!

double <br />Grass...then munchies....I mean...er...umm...nothing. <br />I got to go

 

[Barlow]

Re: Once and for all!

...anybody see the size of that chicken?

 

[jtexas]

Re: Once and for all!

Originally posted by Ralph:<br /> Newton's third law of motion states for every action, there is an equal and opposite reaction.<br /><br />When a car hits a wall going 50 mph, the wall feels the force and so does the car. They feel the same force<br /><br />When the wall moves toward the car at 50 mph (i.e., becomes another car), they both feel the force of 100 but in opposite directions. That is, they feel the force they exerted plus the force the other object exerted.

the wall and the car need to sit down and talk about what they are feeling.<br /><br /><br />but, doesn't a car instantaneously decelerating from 60 to 0 take the same damage whether it was caused by a brick wall or another car also going from 60 to 0? The front of the car stops, but the back keeps going until it can't compress anymore? Or something like that?<br /><br />btw, the human body can survive many times more G's lateraly (acceleration/deceleration) than it can vertically. Something about vertibrae compression, arterial separation, stuff like that.

 

[roscoe]

Re: Once and for all!

Hey Ya'll, Look at this!! Boom.

 

[Ralph 123]

Re: Once and for all!

JT,<br /><br />Here is another way to think about it. When a car is moving at a wall at 50, the force of the impact is Force = Mass * Acceleration (Newton's Second Law). Acceleration is change in velocity divided by the change in time.<br /><br />Now, when the car is moving toward the wall at 50, and the wall is moving toward the car at 50, the effective velocity is 100 so the deacceleration will be twice what it was (in this case) and hence, the force will be twice what it was.

 

[willamettejeff]

Re: Once and for all!

So if a point on the blade of a mower is travelling at 50mph and the mower itself is moving at 3mph is the force with which a blade of grass is struck then that of 53mph? Think carefully.

 

[Ralph 123]

Re: Once and for all!

More complex because the rotation of the blade is circular so it depends where the grass is w.r.t. the blade at time of impact. So, for example, the grass that is struck at a right angle to the blade on the left (assuming CW rotation of the blade) will be struck by a blade with a velocity of 53 Mph parallel to the direction of travel of the mower.<br /><br />The grass directly in front of the mower will be struck by a blade going 50 Mph perpendicular to the travel of the mower plus a force of 3 Mph parallel to the direction of the mower. The net vector velocity will be 50.09 mph at a 79.2 degree angle to the direction of the mower (so because the mower is moving, the strike isn't exactly at 90 degrees like it would be if the mower wasn't moving)<br /><br />So, you do the same thing basically for all the grass struck by the blade. Assuming the blade rotates clockwise, the grass parallel on the left gets struck with a velocity of 53. Those struck on the right get struck with 47. etc, etc<br /><br />Gosh, I haven't done this stuff since the mid eighties! I'm getting OLD!

 

[willamettejeff]

Re: Once and for all!

Excellent Ralph. But did I forget to mention that the mower deck is set to 4 inches and the grass is only 3 inches tall.

 

[Ralph 123]

Re: Once and for all!

LOL That will teach me!

 

[Grant S]

Re: Once and for all!

Ralph,more of the same, the grass on the right doesnt get struck at 47 because it has been cut at 53 and is in the catcher. ;-)<br /><br />Thanks for the explanation.