Water boils at low temperature

Why water boils at lower temperature at high altitudes?
This is because the air pressure is lower at high elevations. Boiling occurs when the water is hot enough to have the same pressure as the surrounding air, so that it can form bubbles. At high altitudes, air pressure is lower than at sea level, so the water doesn't have to get so hot to get to boiling.

Buoyancy

Why does a piece of iron sinks but a ship made of the same iron floats?
To understand this you must know what Archimedes’ Principle is.
Archimedes’ Principle states that a body immersed in a liquid, wholly or partly, loses its weight. The loss of weight is equal to the weight of the liquid displaced by the body. Here the ship floats because the amount of water that they displace, weighs more than the ship itself. It's called the law of Buoyancy.If the buoyant force is greater than the gravitational force, the object will float, but if the opposite is true, the object will sink.

Pulling or Pushing

Which one is easier ‘Pulling or Pushing’?
When you apply force on an object to pull it, the vertical component of the force act in the opposite direction of weight and this decreases the apparent weight of the body. When you push, the vertical component acts in the same direction as that of the weight and more work is to be done to displace the body. Therefore pulling is easier than pushing.

Climb upstairs

Why it is harder to walk up the stairs?
As you climb up the stairs you are carrying your own body
weight against gravity.