Liquid gold is poured into molds and cools to become solid bars. The gold is .
Liquid nitrogen becomes a gas when it is poured out of its container. The nitrogen is
.
Solid iron is heated to high temperatures so that it becomes a liquid. The iron is
.
Water vapor in the air becomes tiny liquid droplets that form fog. The water is
.
In a very cold cryogenic freezer, solid oxygen forms on the walls from the oxygen gas in the air. The oxygen is
.
In the high desert, snow changes to water vapor without becoming liquid water. The snow is
.

(newtons first law)

conservation of momentum law states :

momentum before collision = momentum after collision

momentum p (kg-m/s)= mass * velocity

say moving car=1 000 kg, velocity = 10 m/s then p = 1 000*10= 10 000 kg-m/s

say still car = 2 000 kg, velocity = 0 m/s then p = 2 000* 0 = 0 kg-m/s

total momentum prior to collision = 10 000 + 0 = 10 000 kg-m/s

momentum after collision = 10 000 kg-m/s

mass now = 1 000 kg+2 000 kg = 3 000 kg

10 000 = 3 000 kg* velocity m/s

10 000/3 000 = velocity

3.33 m/s = velocity after collision

an impulse is a force applied over time , momentum is exclusive of external forces and a perfect collision is implied