# I Object dropped from a plane

1. Sep 28, 2016

### Gaboon

Hi all,
I have a very simple question. Will an object dropped from a plane moving at a constant velocity ever achieve purely vertical motion? (Make sure we're not taking air resistance into account)
Thanks

Last edited by a moderator: Sep 28, 2016
2. Sep 28, 2016

### Staff: Mentor

No. If there is no air resistance, the horizontal velocity of the object stays fixed at the velocity of the plane.

3. Sep 28, 2016

### Gaboon

4. Sep 28, 2016

### Staff: Mentor

I don't understand the question. The object follows a projectile trajectory. Are you familiar with the equations of projectile motion with constant acceleration (gravity) and with the simplifying assumption of no air resistance?

5. Sep 28, 2016

### Gaboon

Yes. Does that trajectory ever lead to object falling at 90 degrees to earth?

6. Sep 28, 2016

### Staff: Mentor

No, it can't. The horizontal velocity never decreases, so the object will never fall vertically. The vertical speed keeps increasing when there is no air resistance, so the vertical angle gets smaller and smaller, but it never goes to zero.

7. Sep 28, 2016

### ZapperZ

Staff Emeritus
Only if you fall along with the object.

Zz.

8. Sep 28, 2016

### Gaboon

Ok thanks for feedback. Though I would love to know why the vertical angle never reaches zero.

9. Sep 28, 2016

### ZapperZ

Staff Emeritus
Read Berkeman's reply in Post #2! I have a feeling that the significance of that explanation escapes you somehow.

Zz.

10. Sep 28, 2016

### Staff: Mentor

You'll recognize that if there is always horizontal motion, the angle can't be zero, right? Or are you unclear about why the horizontal speed is fixed? That's due to Newton's first Law.