Work .
工作。
Work is how much force is used to move something.
功是用来移动某物的力的大小。
If you push or pull an object and it moves, work is done.
如果你推或拉一个物体并且它移动，功就完成了。
But if the object does not move, then no work has been done.
但是如果物体没有移动，那么就没有工作完成。
A heavy box is hard to lift.
沉重的箱子很难举起。
A lot of work is needed.
需要做很多工作。
A pulley makes it easier to lift the box.
滑轮使提起箱子更容易。
Less work is needed.
需要更少的工作。
A heavy box is hard to pull.
重箱子很难拉。
There is a lot of friction between the box and the floor.
箱子和地板之间有很大的摩擦。
It is easier to pull the box on a wagon.
用马车拉箱子更容易。
There is less friction between the wagon wheels and the ground.
车轮与地面之间的摩擦力较小。
A heavy wagon is hard to carry upstairs.
沉重的马车很难抬上楼。
It is easier to pull the wagon upstairs on a ramp.
在坡道上拉马车更容易。
Less work is needed.
需要更少的工作。
A seesaw is a lever.
跷跷板是一个杠杆。
It makes it easier to move our friends into the air.
它使我们的朋友更容易移动到空中。