Speed of a falling object


by dalebennett
Tags: falling, object, speed
dalebennett
dalebennett is offline
#1
Nov27-10, 11:48 AM
P: 4
Hey Smart Guys,

At age 61, I am building a mechanical launching device (Trebuchet) and I need to know how fast my counterweight will be traveling.

How fast will it be traveling after 1 inch
How fast will it be traveling after 60 inch
How fast will it be traveling after 120 inch

Also, please provide the travel time to reach each point (1, 60 & 120 in.)

The counterweight surface is flat, weighs 2000 lbs with a square surface area of 1296 Sq Inches. (3'x3')

I don't do formulas very well, so plain English would be much appreciated!

Thanks in Advance,

Dale
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brno17
brno17 is offline
#2
Nov27-10, 01:21 PM
P: 28
Quote Quote by dalebennett View Post
Hey Smart Guys,

At age 61, I am building a mechanical launching device (Trebuchet) and I need to know how fast my counterweight will be traveling.

How fast will it be traveling after 1 inch
How fast will it be traveling after 60 inch
How fast will it be traveling after 120 inch

Also, please provide the travel time to reach each point (1, 60 & 120 in.)

The counterweight surface is flat, weighs 2000 lbs with a square surface area of 1296 Sq Inches. (3'x3')

I don't do formulas very well, so plain English would be much appreciated!

Thanks in Advance,

Dale
Fg=Ek

Force of gravity will convert to Kenetic energy

mgh=1/2mv^2

solve for v
(Devide both sides by m, multiply by 2 and sq rt both sides)

v=sqrt/ 2gh

EDIT: g=gravity at 9.8m/s and h is height in meters and v is also in meters/second

When you find speed you already have distance

v=d/t

t=vd

Multiply the speed in m/s and distance in meters to get the time
Integral
Integral is offline
#3
Nov27-10, 01:27 PM
Mentor
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P: 7,291
There will be some energy lost to friction so the above analysis gives a high estimate. If you need better you will need to figure out a way to measure the velocity.

dalebennett
dalebennett is offline
#4
Nov27-10, 02:43 PM
P: 4

Speed of a falling object


I'm sorry, but I don't understand these equations. Would you be kind enough to do the actual calculation. I flunked out of algebra.
Tide
Tide is offline
#5
Nov28-10, 12:46 AM
Sci Advisor
HW Helper
P: 3,149
The answer depends on what kind of trebuchet you want to build. In addition, you need to specify things like the length, weight and shape of the beam and where the axle is in relation to both the counterweight and payload.
dalebennett
dalebennett is offline
#6
Nov28-10, 09:20 AM
P: 4
Actually, I just want to use this information as a reference point. For now, all I need are the raw answers. Please, just disregard the Trebuchet design for now. If you are interested in this project, I would be extremely interested in providing you more detail a little later.

This is a new concept for a Trebuchet and there are many physics questions that will need to be answered. For now, just the basic math, please.

I'm planning a 1 mile launch that has never been done before.
DaleSwanson
DaleSwanson is offline
#7
Nov28-10, 05:03 PM
P: 351
http://www.google.com/search?&q=sqrt...inch%29+in+mph

You can easily change the distance to any distance you want to find.
dalebennett
dalebennett is offline
#8
Nov28-10, 05:50 PM
P: 4
I copy/pasted that equation exactly as show into Excel and it did NOTHING.

Is '1 inch' suppose to be embedded into the equation?

What value do I change. I'm am truly sorry for my ignorance.

Can you give it EXACTLY as it should be put into an excel cell - for 1 in and 2 inches - then I will know how to modify the equation for any distance?

the following was the last thing I tried.

=sum(sqrt(2*(9.8(m/(s^2)))*1))

Obviously, I don't know what I'm doinh

Thanks for your patience.

Dale
JolileChat
JolileChat is offline
#9
Nov28-10, 05:54 PM
P: 32
http://www.uni-siegen.de/fb11/nm/akt...chet_adams.pdf

This might be useful for you, in particular the model described in figure 5(c).
Tide
Tide is offline
#10
Nov28-10, 07:46 PM
Sci Advisor
HW Helper
P: 3,149
In the absence of any design specifications the best you can do is set limits for speed and time based on a free falling counterweight.

For what it's worth, here's what you get for the numbers:

1 inch: Max speed = 2.3 feet per second, Min time = 0.072 seconds
60 inch: Max speed = 18 feet per second, Min time = 0.56 seconds
120 inch: Max speed = 25 feet per second, Min time = 0.79 seconds
DaleSwanson
DaleSwanson is offline
#11
Nov28-10, 08:48 PM
P: 351
Quote Quote by dalebennett View Post
I copy/pasted that equation exactly as show into Excel and it did NOTHING.
That wasn't intended to be used in excel. Google has a built in calculator that understands units and constants. If you click the link you should see 1 inch gives an answer of 1.578 mph. If you want to change the distance you do so in the Google search box. You should notice that if you, for example, change 1 inch to 3 feet the answer pops up in a box directly below the search box. You don't even have to click search.

If you want to use excel the formulas should be:
=SQRT(2 * 32.174 * 1) <- one foot, answer is 8.02 feet per second
=SQRT(2 * 32.174 * 2) <- two feet, answer is 11.34 feet per second
=SQRT(2 * 386.09 * 1) <- one inch, answer is 27.79 inches per second
=SQRT(2 * 386.09 * 2) <- two inches, answer is 39.3 inches per second
Pay careful attention to the difference between inches and feet in the above forumulas. Like I said, Google understands units and does the conversions for you. Excel does not, and you have to manually do the conversions.
MagnetDave
MagnetDave is offline
#12
Nov29-10, 03:04 AM
P: 62
There's a trebuchet simulator that is probably more useful for you:

http://www.trebuchet.com/sim/


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