If an arm is stretched forward under water resistance is increased and a reaction force back ward is developed both of which would contribute to negative acceleration.

如果手臂在水中是向前伸展则阻力会随之增加而向后方的反作用力也会出现，二者都会产生负加速度。

youdao

Here, when it makes this rounding curve the velocity is positive here, but on this side it's negative so what does that mean for the acceleration?

这里，就在曲线的拐角，速度一开始是正的，不过在另一边就成了负的，就加速度而言这又意味着什么呢？

youdao

However, if you take the average acceleration t1 0 that is smaller than zero 0 because here the velocity is zero but here the velocity is negative.

可是如果考虑到,和t5之间的平均加速度5，between，t1，and，t5,那么它将小于,因为这里速度为,但是到了这里却是负值。

youdao

As you start on the top and go down, your acceleration is negative.

当你在顶楼准备下降的时候,你的加速度是负的

耶鲁公开课 - 基础物理课程节选

It tells you when a particle moves in a circle, it has an acceleration in a negative R direction, namely directed towards the center.

它告诉你当一个物体在圆周上运动时,它有一个在 -R 方向的加速度,也就是说是直接指向圆心的

耶鲁公开课 - 基础物理课程节选

Remember, you've got to keep track of the sign of acceleration, so if you're picking up speed towards the ground, a is negative, so it will be g plus a, but a is a negative number.

记住,一定要注意加速度的符号,所以当你加速下降的时候,a 是负的,还是 g 加上 a,但是 a 是负数

耶鲁公开课 - 基础物理课程节选