It was all very interesting but tbh I'd rather everyone had been discussing the physics in colliding galaxies
It's actually an extremely slow process, as in hundreds of millions of years.
Our galaxy is currently eating a smaller galaxy. mmm, delicious.
Nope, this collision is mostly inelastic since we have deformation (crumple zones). If it was elastic everything would bounce away again.
Well we generally work with the assumption that the mass of the wall is so great it's basically an immovable obstacle. Regardles though, it's velocity is zero therefore it's acceleration is zero and it doesn't generate any force. The only force the wall applies to the car is from Newton's third law (equal and opposite to the force the car applies on the wall).
To be a bit more general about this, if a small mass traveling at velocity v hits an infinitly greater mass the small mass will lose it's velocity. Change in velocity over time is acceleration therefore there is a force causing the loss of velocity. If it hits an equal mass traveling in the opposite direction at the same velocity this would be equivalent (see below)
If I put a plane on a giant treadmill which matched the speed of the plane in the reverse direction, and it took off and crashed into a wind powered vehicle travelling downwind faster than the wind at 120mph, would it be equivalent to crashing it into a stationary deer made from concrete (modelling the deer as a non deformable, non movable block)?
1. As power said the plane will not take-off. It's stationary therefore there is no lift blah blah
too lazy to get into that2. Remove the treadmill, the plane takes off. Let's use momentum for this (mass multipied by velocity). If the momentum of the plane is the same as the momentum of the wind-powered object they will cancel out since they're in opposite directions (net momentum of the system after collision is zero)
If your concrete deer is a non deformable, non movable block it's momentum must be zero both before and after collision therefore the net momentum of the system after the collision is zero as is the plane's.
So to summarise, in the case of equal momentums they are equivalent. Otherwise they're not since the net momentum of the system will be non-zero after collision. (with the cars they move at the same speeds and have equal masses therefore they have equal momentums)
If the deer had eyes I'm sure they would be very wide caught in the plane's lights...
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