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- Thread starter shamrock5585
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Yeah, that would give you the impulse - the force integrated over the entire collision. To compute the force at any given time you need the duration of collision and a lot more information - colliding objects tend to compress, then expand, so the force isn't constant.

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ok so the force integrated over the entire collision would be the average force applied...

That's not quite true. The impulse is independent of the duration, the average force is not. To get the average force you can divide the impulse by the duration.

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p=mv

p=(Fnet)*(Δt)

therefore...

(Fnet)*(Δt)=mv

Fnet=(mv)/(Δt)

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yes the pressure that is applied is different but that is still dependant on the force... im not really even sure whos response your refering to anyway

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HallsofIvy

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The average force a ball moving at velocity v, exerts striking a steel plate will be quite different from the average force exerted by an identical ball, also moving at velocity v, striking a soft pillow.

A ball moving at velocity v has a specific

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ok if you want to pick apart my wording... if the ball didnt have a velocity in the first place then it wouldnt exert a force on the object it is striking other than its own weight (if it is being dropped). so the force is due to its change in velocity, hows that for wording.

The force that the ball exerts on the steel and the pillow is different because the duration of the impact is different.

The force that the ball exerts on the steel and the pillow is different because the duration of the impact is different.

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W = work

F= force

P = power

[tex]W = Fs[/tex]

[tex] \frac{dW}{dt} = \frac{d(Fs)}{dt} [/tex]

[tex] \frac{dW}{dt} = F \frac{ds}{dt} [/tex] ..............assuming the force is constant

[tex] P = Fv [/tex]

[tex] F = \frac{P}{v} [/tex]

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HallsofIvy

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Still wrong. Force= mass*acceleration. Force is due took if you want to pick apart my wording... if the ball didnt have a velocity in the first place then it wouldnt exert a force on the object it is striking other than its own weight (if it is being dropped). so the force is due to its change in velocity, hows that for wording.

Exactly. So you cannot calculate the force given only the velocity. My point is that you should not worry about your inability to find a formula relating force to velocity because there isThe force that the ball exerts on the steel and the pillow is different because the duration of the impact is different.

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russ_watters

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No, an object only exerts a force when it is accelerating.is there a way to calculate the force that an object will exert when it is moving at a certain velocity... force equals mass times acceleration, but if an object is travelling at a high rate of speed it will exert a greater force than if it were at resteven if it is not accelerating. [emphasis added]

The first part is correct, which should tell you clearly that the answer to the question at the end is no.The only way i can see to find the force is to find how long the impact takes which would be a very small amount of time and then divide your velocity by that to get your deceleration... so then your deceleration/acceleration times the mass of the object is the force it will exert when it strikes something... is there a way to calculate the force without knowing how long the impact takes?

Same question as above, same answer: no.so theres no way to figure out what the average force would be without the time duration of the impact?

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ok you guys are picking apart my wording way too much... im sorry if it is not perfectly clear to you...

sorry halls of ivy... rate of change of velocity not change in velocity. I was pretty sure you knew what i was talking about but i guess i have to be extra clear.

Russ i was saying if it was not accelerating because i was clarifying that the object has constant velocity. it would decelerate at impact but i was clarifying that it was not accelerating initially in motion.

i know that the force distribution is different on impact for different materials because of compression. what i was suggesting was that if you knew a material constant for impact on a material, couldnt it be possible to predict the force it would exert if it struck at a certain velocity.

sorry halls of ivy... rate of change of velocity not change in velocity. I was pretty sure you knew what i was talking about but i guess i have to be extra clear.

Russ i was saying if it was not accelerating because i was clarifying that the object has constant velocity. it would decelerate at impact but i was clarifying that it was not accelerating initially in motion.

i know that the force distribution is different on impact for different materials because of compression. what i was suggesting was that if you knew a material constant for impact on a material, couldnt it be possible to predict the force it would exert if it struck at a certain velocity.

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russ_watters

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Yes, but it can be complicated. For metal objects it isn't too bad because they deform elastically for quite a bit of energy absorption. So you can model the impact as a spring-mass system, with the kinetic energy before the collision being equal to the potential energy after (but before any rebound). In that case, the impact force increases linearly with distance and parabolically (I think - you may want to try to derive that...) with duration of the impact.what i was suggesting was that if you knew a material constant for impact on a material, couldnt it be possible to predict the force it would exert if it struck at a certain velocity.

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an object with

therefore F=m*0=0 and therfefore, no force.

When it hits an object, it decelerates (negative acceleration). This acceleration is used to calculate the force of the impact. The higher the velocity if the object before impact, the larger it's deceleration would have to be to bring it to a stop during impact and therefore a larger force would be generated at impact.

No need for the twin paradox, it is basic classical mechanics (with velocities well below c, of course )

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ok you guys are picking apart my wording way too much... im sorry if it is not perfectly clear to you...

sorry halls of ivy... rate of change of velocity not change in velocity. I was pretty sure you knew what i was talking about but i guess i have to be extra clear.

Russ i was saying if it was not accelerating because i was clarifying that the object has constant velocity. it would decelerate at impact but i was clarifying that it was not accelerating initially in motion.

i know that the force distribution is different on impact for different materials because of compression. what i was suggesting was that if you knew a material constant for impact on a material, couldnt it be possible to predict the force it would exert if it struck at a certain velocity.

I'm new and thought your conversation fasinating - Force due to mass and velocity: 2 students were jogging in the gym one male 6'4 170lbs and the other female 5'2 120lbs. Both were jogging 6m/s then increased their velocity to 10m/s. They maintained that pace for 5s when both unfortunately ran into another student. At what force was that impact?

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cjl

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F=mA

F=m * dv/dt

Velocity is equally responsible for force as acceleration is! One could argue that there IS force due to velocity. The rate of change of velocity. lol

If you think of a macroscopic object moving in space, it could be said to have a velocity with respect to another object but it can never be said to not be accelerating because it is forever being acted on by all the other particles forces in the universe... and as such is acting back on all other particles in the universe.

So by virtue of the fact that the object is moving from one point to another at a given fixed velocity with respect to another object, it is imparting forces on all other objects in the universe.

There is no velocity without acceleration.

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russ_watters

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No, velocity is not equally responsible as acceleration. You might say velocity change and time elapsed are equally responsibe, since they are both part of the formula for acceleration, but even that isn't very useful.Interesting semantics.

F=mA

F=m * dv/dt

Velocity is equally responsible for force as acceleration is! One could argue that there IS force due to velocity. The rate of change of velocity. lol

Ie, if you have acceleration and mass, you can find force. If you have dv and mass, you can't find force. That makes one more useful than the other for finding the force.

No. That's gravity you are talking about and it acts just fine with or without motion.If you think of a macroscopic object moving in space, it could be said to have a velocity with respect to another object but it can never be said to not be accelerating because it is forever being acted on by all the other particles forces in the universe... and as such is acting back on all other particles in the universe.

So by virtue of the fact that the object is moving from one point to another at a given fixed velocity with respect to another object, it is imparting forces on all other objects in the universe.

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