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August 16th, 2016, 11:47 AM   #1
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Mass Collision With No Impact

Before I had this idea that it was impossible for two objects to collide without ANY impact. No matter how slow they are moving when they collide, there will still be some amount of impact. And if the object is moving at a rate of 0, then it cannot collide with anything.

But recently I have thought of a way for two objects, with mass, to collide without any impact. In theory, that is. I encourage you, before I explain, to try and imagine a situation where this is possible.

So let's imagine a graph where the x = time, and y = distance. So imagine a function curve that intercepts the x axis. If that function curve represents movement, then the point by which it intercepts the x axis can be expressed as a collision with the x axis. The greater the slope of the equation is when it intercepts, the greater the impact is since x = time.

Now let us imagine a sphere with an exact radius of 1. Suppose the x axis is a wall and the sphere takes a motion path of y = x^2+1. y represents the distance from the exact center of the ball. Now when x or time = 0, the ball is touching the x axis wall. But the slope of the equation at that point is 0. That means there was no impact! The velocity of the moving ball keeps getting lower and lower, and when it collides with the wall the impact power is 0.

You can imagine this in a real world problem by throwing a ball at the ceiling of a house for example. If the ball's maximum height is = to the ceiling height, then the ball touches/collides into the ceiling without any impact.

What are you guy's thoughts on this?
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August 16th, 2016, 01:54 PM   #2
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Honestly! So what. If you wish to call grazing contact no impact so be it.
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August 16th, 2016, 03:28 PM   #3
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What are you guy's thoughts on this?
This is called "touching" in Physics and many problems in Physics use this term.

For example: You fire a projectile with an initial speed of 10 m/s at an angle of 35 degrees above the horizontal. What is the speed of the object when it lands?

There are one or two students per semester that say the speed must be 0 m/s because it has landed. But what the question is talking about is what is the speed of the projectile when it touches the ground.

-Dan
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August 16th, 2016, 10:13 PM   #4
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Honestly! So what.
Just thought it was a interesting idea.
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August 17th, 2016, 09:13 AM   #5
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The velocity of the moving ball keeps getting lower and lower, . . .
For, say, a rolling ball (on a fixed surface, and ignoring deformation of either the ball or the surface), has its point in contact with the surface collided with the surface or just momentarily come to rest against the surface?
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August 17th, 2016, 03:01 PM   #6
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For, say, a rolling ball (on a fixed surface, and ignoring deformation of either the ball or the surface), has its point in contact with the surface collided with the surface or just momentarily come to rest against the surface?
Because of gravity, there is a slight downward force as it passes over each point. I am not sure what "collision" means in this case.
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August 17th, 2016, 11:42 PM   #7
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For, say, a rolling ball (on a fixed surface, and ignoring deformation of either the ball or the surface), has its point in contact with the surface collided with the surface or just momentarily come to rest against the surface?
Expanding skipjack's idealisation I would say that a ball rolling down a curved (concave upwards) ramp which becomes tangent to a flat horizontal surface suffers no impact as it transfers from the ramp to the horizontal surface.

As skipjack noted this requires perfectly rigid balls, ramps and surfaces.

Last edited by studiot; August 17th, 2016 at 11:59 PM.
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