# Find velocity and acceleration (positive or negative)

1. Sep 15, 2014

### Kerrie yu

What would the velocity and acceleration be if a person was tossing a ball upward but downward direction is positive? When the ball was falling down, what would the velocity and acceleration be?

2. Sep 15, 2014

### KurtWagner

On the way up, your acceleration would be down (positive) and your velocity would be up (negative).

Once the ball is falling, the acceleration is still down (positive) and the velocity is down (positive)

3. Sep 15, 2014

### KurtWagner

... Assuming there is gravity

4. Sep 15, 2014

### Kerrie yu

But wouldn't there be a difference since the downward direction is positive

5. Sep 15, 2014

### Kerrie yu

Oh wait,,, nvmm thxx

6. Sep 15, 2014

### KurtWagner

Its also cool to note that even at the top of the motion, when the velocity is zero, the acceleration is still in the down (positive) direction.

7. Sep 15, 2014

### Kerrie yu

Oh yea,, its something like the acceleration cannot be 0 because if it is , it againsts the gravity ...something like that..right?

8. Sep 15, 2014

### KurtWagner

Gravity is always accelerating the object. But the object has to stop before going backward (has to be 0 velocity). This is a really really really small time though.

9. Sep 15, 2014

### CWatters

I assume you are talking about what happens after it leaves the mans hand while subject to gravity (eg not while he's actually throwing it).

On the way up....

The displacement is negative
The velocity is negative
The acceleration is positive

After max height on the way down...

The displacement is initially still negative but then it goes positive as it passes the origin.
The velocity is positive
The acceleration is positive