If we think about this green object moving to the right,

如果我们考虑这个绿色物体向右边运动
to the left, to the--to your left

向左边不向你们的左边
then there must be a force

那必须有一个力
that's creating the motion to the left and that force

迫使它向左运动
is just big enough to overcome the resistance to motion.

而这个力正好能抵消阻力
That force is equally balanced with whatever force resists motion.

不管阻力是多少受力都是恰好平衡的
Of course the force that resists motion is going to be different

当然阻碍运动的力可以有很多种
if you're an organism that's trying to fly,

对于一个想飞的生物
than if you're an organism that's trying to move along the ground,

或者一个想在地上运动的生物
than if you're an organism that's trying to swim.

或者一个想游泳的生物阻力都各不相同
So, what we're going to think about today are the forces

所以我们今天来考虑一下运动的阻力
that resist that motion and how organisms overcome that resistance.

以及生物是如何克服这种阻力的