# B General Physics Question -- Max height of a projectile

1. Jun 25, 2017

### Jerret Spenst

When an object is thrown or propelled upwards and it meets the point at deceleration and drops; what is that point called, where the object is not moving in either direction?

2. Jun 25, 2017

### Staff: Mentor

Welcome to the PF.

"Point of inflection?"

3. Jun 25, 2017

### Staff: Mentor

4. Jun 25, 2017

### Jerret Spenst

Thank you! Now in that state, could you propose that there would be a new force acting on the object or even the loss of one.

5. Jun 25, 2017

### Staff: Mentor

Neglecting air resistance, there is only the force of gravity acting on the thrown object, and its acceleration (downwards) is constant.

6. Jun 25, 2017

### Staff: Mentor

7. Jun 25, 2017

### Jerret Spenst

True, but I'd like to discuss the possibility of theoretical forces not yet discovered or applied to general physics.

8. Jun 25, 2017

### Staff: Mentor

We don't allow speculation or theory development at the PF. We discuss mainstream science, as published in the peer-reviewed literature and mainstream textbooks.

9. Jun 25, 2017

### Jerret Spenst

Not a problem! Thank you for the previous answer!

10. Jun 25, 2017

### sophiecentaur

Why bother trying to introduce an extra force when the whole classical process can be calculated and predicted as accurately as you choose, using the existing classical forces - until you get to the scale of Relativity or QM.
PF protects itself (and you) from such whimsy.

11. Jun 28, 2017

### RTM

If an object is propelled straight up from ground level, and is unaffected by wind or other forces, and it takes say, 4.6 seconds for it land back down, can it's max height be calculated? If so, what's the answer and math? Thanks!

12. Jun 28, 2017

### Staff: Mentor

Are you familiar with the Kinematic Equations of Motion for Constant Acceleration (gravity)?

13. Jun 28, 2017

### RTM

Yes, but long time. Will brush up on it, and figure it out! Will be a good exercise. Thanks!

14. Jun 28, 2017

### Staff: Mentor

The Hyperphysics website has a concise summary:

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

The Wikipedia page for Equations of Motion is good too, with lots more detail. I think the equations for motion given constant acceleration are about halfway down the long Wikipedia page...

15. Jun 28, 2017

### Staff: Mentor

Oops, that Hyperphysics link takes you to the top level. Click on Mechanics in the upper left, and then on Velocity and Acceleration...

16. Jun 28, 2017

thank you.