Why not? What if you lower the box?D. Wani said:Can work done against gravity be negative? (In the sense that the angle between displacement and force is zero)
The work must be negative aganst the whatever you want force. And it always is! In condition if the "whatever you want force" direction is accepted as possitive. You still think about things that are not actual for you. All should be done in sequence. Let you understand what is work of force against another force is. The other things after that.D. Wani said:Can work done against gravity be negative? (In the sense that the angle between displacement and force is zero)
In my earlier man and box example, when both F and s were in the same direction, work done "by the man" was positive and hence, he lost energy. In the next example also, work done by the man was positive and that by gravity was negative, hence, man lost energy and the body gained gravitational PE. So, by convention, whoever does positive work, loses energy and whoever does negative work, gains energy. If you want to do 'negative' work 'against' gravity, you should gain energy i.e.you should impede the body's motion "due to" gravity. When you catch a free-falling ball, the ball's motion is due to gravity and you impede it, thereby doing negative work against the gravity. Hence, you(your hands actually) gain the energy lost by the ball.D. Wani said:Can work done against gravity be negative? (In the sense that the angle between displacement and force is zero)
That is thermodynamical look on a things. But in mechanical sense it absolutely does not metter what force works against to another.cnh1995 said:So, by convention, whoever does positive work, loses energy and whoever does negative work,