August 16th, 2016, 11:47 AM  #1 
Senior Member Joined: Jul 2016 From: USA Posts: 108 Thanks: 13  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? 
August 16th, 2016, 01:54 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,835 Thanks: 733 
Honestly! So what. If you wish to call grazing contact no impact so be it.

August 16th, 2016, 03:28 PM  #3 
Math Team Joined: May 2013 From: The Astral plane Posts: 2,304 Thanks: 961 Math Focus: Wibbly wobbly timeywimey stuff.  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 
August 16th, 2016, 10:13 PM  #4 
Senior Member Joined: Jul 2016 From: USA Posts: 108 Thanks: 13  
August 17th, 2016, 09:13 AM  #5 
Global Moderator Joined: Dec 2006 Posts: 21,035 Thanks: 2271  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?

August 17th, 2016, 03:01 PM  #6 
Global Moderator Joined: May 2007 Posts: 6,835 Thanks: 733  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.

August 17th, 2016, 11:42 PM  #7  
Senior Member Joined: Jun 2015 From: England Posts: 915 Thanks: 271  Quote:
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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