When a liquid or a gas is heated, it expands and becomes less dense, so it rises, while the cooler, denser liquid or gas sinks. (Not sure if this helps but this is what I hit)
Answer:
In an elastic collision, the momentum is conserved and the mechanical energy is conserved too.
Explanation:
There are two types of collisions:
- Elastic collision: in an elastic collision, the total momentum before and after the collision is conserved; also, the total mechanical energy before and after the collision is conserved.
- Inelastic collision: in an inelastic collision, the total momentum before and after the colllision is conserved, while the total mechanical energy is not conserved (in fact, part of the energy is converted into other forms of energy such that thermal energy, due to the presence of frictional forces)
Answer: it is due to friction.
Explanation: if you were to push an object that is at rest, there is static friction that you would first need to overcome. An example would be pushing a car as it is in neutral. Pushing it takes more force and work to overcome that friction.
But once it overcomes static, it will then turn to kinetic friction. Once the car starts to move, you notice that it is easier to push. This is due to the fact that kinetic friction would equal normal force times the constant while the static friction is greater than or equal to the normal force times the constant.
Hope this helps!!!
