At the time of climbing the hill or breaking the stairs you have to push your body upwards, whereas you don't have to do, while getting down. It’s the Gravity. When you are climbing up, gravity will be working against you, pulling you down and hence you have to pose more force.

Sailboats can't sail directly against the wind, but they can sail using sail on it. Because of the interaction between the lift generated by the sails in the air and the boat in the water. Sails, with momentum, generate lift like an airplane wing perpendicular to the flow of air across them.

When an object is raised from the surface of the Earth, its distance from the center of the Earth increases, resulting in a decrease in the gravitational force acting on it. As gravitational force weakens with height, the object's weight decreases. 

If the elevator descends freely, the cord of the elevator is torn, below the acceleration “g”, a person within the elevator feels weightless.

If the elevator descends the acceleration “g”, a person within the elevator feels less than the original weight.

The weight of a person standing in a descending lift decreases because the lift is accelerating downward. When the lift moves down, the person experiences a reduction in the normal force exerted by the floor of the lift, which is what we feel as weight. This is due to the relative motion between the person and the lift, leading to a feeling of lighter weight. If the lift were in free fall, the weight would become zero.

When a lift descends the apparent weight of a standing person inside it decreases as weight R=mg-ma=m(g-a).

The weight of an object on the earth is equal to multiplication of its mass and gravitational acceleration of the earth. The moon has one-sixth the acceleration than the earth. Hence, if an object is taken to moon, its weight will be reduced to one-sixth of the earth.

The weight of an object is greatest in the polar region because the Earth is slightly flattened at the poles and bulges at the equator due to its rotation. This means the distance from the Earth's center to the poles is shorter than at the equator. Since gravitational force is stronger when objects are closer to the Earth's center, an object weighs more at the poles than at the equator.

Astronauts, orbiting the earth, do feel weightless as there is no ground or any other force to counteract the force of gravity; i.e. the astronauts orbiting the earth have acceleration equal to gravity.

As the mountain slope is inclined at an angle from the normal ground, our body leans forward so that center of gravity becomes low in order to maintain the equilibrium position, provided that we don’t fall on our back.

Lubrication system first used by Wright Brothers. This system is considered to reduce temperature caused by friction between sliding or rolling parts, give a flow to the clean oil at the accurate temperature, with appropriate pressure to each part of the engine.