#1

I searched and couldn't find a science thread so I must post here again (sorry!)

A squirrel drops an acorn from a tree branch that is 8 m from the ground.

1. How long is the acorn in the air?

2. What is the acorn's velocity when it reaches the ground?

Now I am using a simple program called the moving man, in which you input acceleration, position, velocity. Then it shows you the results.

I typed in 8 for the position and -9.8 for the acceleration. and the answers I get are:

About 1.3 for #1

About -12.3 m/s for #2

That seemed weird and I checked the program and it keeps changing the acceleration without me doing anything. So basically is this the right answer or is my program messing up and it's not right at all.

A squirrel drops an acorn from a tree branch that is 8 m from the ground.

1. How long is the acorn in the air?

2. What is the acorn's velocity when it reaches the ground?

Now I am using a simple program called the moving man, in which you input acceleration, position, velocity. Then it shows you the results.

I typed in 8 for the position and -9.8 for the acceleration. and the answers I get are:

About 1.3 for #1

About -12.3 m/s for #2

That seemed weird and I checked the program and it keeps changing the acceleration without me doing anything. So basically is this the right answer or is my program messing up and it's not right at all.

#2

#3

Why are you making acceleration negative? The acorn will be increasing speed, not decreasing.

#4

Why are you making acceleration negative? The acorn will be increasing speed, not decreasing.

Gravity is a downward or negative acceleration, that's why.

#5

v = inital_v + a * t

current_h = intial_h + initial_v*t + a*t^2/2

initial_v = 0

initial_h = 8m

current_h = 0m

solve for t

when you have t put it into the above formula for v

vectors biatch

current_h = intial_h + initial_v*t + a*t^2/2

initial_v = 0

initial_h = 8m

current_h = 0m

solve for t

when you have t put it into the above formula for v

Why are you making acceleration negative? The acorn will be increasing speed, not decreasing.

vectors biatch

*Last edited by seljer at Nov 15, 2008,*

#6

Be real philosophical about it and say, "technically, the acorn is always in the air...and when it reaches the ground, acceleration is zero, because it stopped."

#7

Be real philosophical about it and say, "technically, the acorn is always in the air...and when it reaches the ground, acceleration is zero, because it stopped."

thats not philosophical

thats just newtonian physics and inertial/noninertial frames of reference

#8

Gravity is a downward or negative acceleration, that's why.

vectors biatch

Exactly this.

The acorn is moving down, and so is the acceleration, hence they are in the same direction so acceleration is positive. You get a negative velocity because, just as you are with acceleration, considering the positive direction to be upwards. Remember velocity is also a vector.

#9

thats not philosophical

thats just newtonian physics and inertial/noninertial frames of reference

I thought I could pull the wool over their eyes. Your exposition of my work tells me that you are indeed a worthy adversary...

Besides, YOU'RE a newt.

#10

So is my program correct?

#11

So is my program correct?

http://www.google.com/search?hl=en&safe=off&client=firefox-a&rls=org.mozilla%3Aen-GB%3Aofficial&hs=POr&q=sqrt(2*8m%2F9.8m%2Fs%2Fs)&btnG=Search

http://www.google.com/search?hl=en&safe=off&client=firefox-a&rls=org.mozilla%3Aen-GB%3Aofficial&hs=s3B&q=sqrt(2*8m%2F9.8m%2Fs%2Fs)*9.8m%2Fs%2Fs&btnG=Search

#12

Try working it out by hand using SUVAT equations?

Oh gorramit, I'll do it for you.

My answers:

v=12.52

t=1.27

So yeah, seems about correct.

EDIT: Will post worked solutions, hang about.

s=8 m

u=0 m/s

v=?

a=9.81

t=?

v^2 = u^2 + 2as

v = Square root (u^2 + 2as)

v = Sq rt ( 2as)

= Sq rt (2x9.81x8)

= 12.52 m/s

v = u + at

t = (v-u)/a

=(12.52-0)/9.81

=1.27s

Oh gorramit, I'll do it for you.

My answers:

v=12.52

t=1.27

So yeah, seems about correct.

EDIT: Will post worked solutions, hang about.

s=8 m

u=0 m/s

v=?

a=9.81

t=?

v^2 = u^2 + 2as

v = Square root (u^2 + 2as)

v = Sq rt ( 2as)

= Sq rt (2x9.81x8)

= 12.52 m/s

v = u + at

t = (v-u)/a

=(12.52-0)/9.81

=1.27s

*Last edited by LordBishek at Nov 15, 2008,*

#13

Umm you guys it's not negative acceleration. It's positive.

Acceleration is only negative when it is in the opposite direction that is in a real life situation when it's deceleration. Suppose a car is reducing speed then you'd have negative acceleration. Gravity is positive acceleration cause it increases speed not reduces.

Suppose you throw a ball up and it reduces speed due to gravity, then it will be negative acceleration. Not cause it's gravity but because it's causing the object to slow down.

Sorry to break your bubble...I enjoyed it

Acceleration is only negative when it is in the opposite direction that is in a real life situation when it's deceleration. Suppose a car is reducing speed then you'd have negative acceleration. Gravity is positive acceleration cause it increases speed not reduces.

Suppose you throw a ball up and it reduces speed due to gravity, then it will be negative acceleration. Not cause it's gravity but because it's causing the object to slow down.

Sorry to break your bubble...I enjoyed it

#14

i wish i was clever enough to post something worth posting in here

#15

Umm you guys it's not negative acceleration. It's positive.

Acceleration is only negative when it is in the opposite direction that is in a real life situation when it's deceleration. Suppose a car is reducing speed then you'd have negative acceleration. Gravity is positive acceleration cause it increases speed not reduces.

Suppose you throw a ball up and it reduces speed due to gravity, then it will be negative acceleration. Not cause it's gravity but because it's causing the object to slow down.

Sorry to break your bubble...I enjoyed it

It can be negative OR positive. It depends entirely upon your inertial frame of reference. If a car was accelerating from left to right, it would be DECELERATING from right to left with equal and opposite magnitude.

#16

Umm you guys it's not negative acceleration. It's positive.

Acceleration is only negative when it is in the opposite direction that is in a real life situation when it's deceleration. Suppose a car is reducing speed then you'd have negative acceleration. Gravity is positive acceleration cause it increases speed not reduces.

Suppose you throw a ball up and it reduces speed due to gravity, then it will be negative acceleration. Not cause it's gravity but because it's causing the object to slow down.

Sorry to break your bubble...I enjoyed it

The book states:

When analyzing free fall, whether you treat the acceleration as positive or negative depends upon the coordinate system that you use. If your coordinate system defines upward to be a positive direction then the acceleration due to gravity is equal to -g.

If your you decided that downward is a positive direction then acceleration due to gravity is +g

So could it not be either?

#17

The book states:

When analyzing free fall, whether you treat the acceleration as positive or negative depends upon the coordinate system that you use. If your coordinate system defines upward to be a positive direction then the acceleration due to gravity is equal to -g.

If your you decided that downward is a positive direction then acceleration due to gravity is +g

So could it not be either?

yes.... if you really wanted to you could point your coordinate system 30° off the z axis towards the northwest or something

#18

The book states:

When analyzing free fall, whether you treat the acceleration as positive or negative depends upon the coordinate system that you use. If your coordinate system defines upward to be a positive direction then the acceleration due to gravity is equal to -g.

If your you decided that downward is a positive direction then acceleration due to gravity is +g

So could it not be either?

It is convention with free fall to take it as positive acceleration with respect to the Earth, or whatever source of gravity, but yes, you're right, it depends. That's why you got a negative velocity. Because you effectively designated your positive direction as going UP instead of down. Since the acorn was falling DOWN, it could be said to move NEGATIVELY with respect to up. Notice that your velocity's magnitude hasn't changed, only it's sign.

#19

Yeah that's cause i like to consider my gravity as positive...

Just me guys !! You can be the rebels you are and consider it negative

And TS, no matter the sign convention the magnitudes should be the same...Your program works as far as i'm concerned

Just me guys !! You can be the rebels you are and consider it negative

And TS, no matter the sign convention the magnitudes should be the same...Your program works as far as i'm concerned

cammo_1234

9,939

195,293

Last post:

Shirtzie

5

443

Last post:

xxunder-takerxx

16

6,998

Last post: