walking up stairs

Late tonight, my brother decided to walk up the stairs to my sister's room because he needed to give my sister a remote control for the television. When he picked up the remote control, he added energy to it (potential energy = mg x height). No work was done to the remote when he was walking around on a flat surface (work requires that there is force and a movement in the same direction as the force exerted on the object), but when he reached the stair case, work was exerted onto the remote control (because the vertical force he is exerting to keep the remote control in the air is now moving in a vertical motion).

One may wonder how my brother could be moving in a vertical motion even though my brother is not going straight upward. This is because his movement (which is diagonal) can be split into vectors. When splitting the movement into vectors, there are two components: a vertical force and a horizontal force. To find the magnitude of the vertical component, one would multiply the magnitude of the overall vector with the sine of the angle of the force.

How amazing it is that my brother walking up and down stairs can trigger Physics thoughts!