# Velocity / Speed loss by shifting to a larger radius

If there was a free-spinning effective weight of 20 lbs. at a 20" radius rotating at 180 rpm (15.7 fps?) and a force of 20 foot pounds was added, what would be the increase in velocity/speed? (Ignoring friction and wind losses).

mfb
Mentor
How do you "add" a force to an object?

Is this a homework question?
What do you expect?

I am an independent inventor. This is not homework. I already have a degree, it is just not in Engineering. The force I am adding is rotational force or torque. This is a device I am building and I am looking to optimize the design. Ideally I would like to know the "payoff" for the input of energy into the system. The source of the force is not important. It could be as basic as a push from a human being's hand.

Baluncore
2021 Award
If there was a free-spinning effective weight of 20 lbs. at a 20" radius rotating at 180 rpm (15.7 fps?) and a force of 20 foot pounds was added, what would be the increase in velocity/speed?
While the force was applied the RPM would continuously accelerate.

While the force was applied the RPM would continuously accelerate.
Thanks for the reply... I guess I am not good at stating the problem, sorry for the lack of Engineering savvy....Assume for illustrative purposes that 20 pounds was added to the downstroke for a distance of one foot and was removed immediately after that one foot of distance. What I am, basically, looking for is the effect on one rotation. Specifically, I wish to find out what is the maximum gain in velocity from that one input of 20 foot lbs. for one revolution.

mfb
Mentor
You can calculate the moment of inertia of your object, and the kinetic energy as function of its speed follows from that. You have the initial energy, and you increase this by 20 pounds * 1 foot, so you know the new energy, which you can convert back to angular velocity.

You should consider using SI units, as imperial units are just a huge mess if you want to calculate anything.

Baluncore
2021 Award
Assume for illustrative purposes that 20 pounds was added to the downstroke for a distance of one foot and was removed immediately after that one foot of distance.
What is a “downstroke”? Is this a vertical axis or horizontal axis rotation?

Your title “Velocity / Speed loss by shifting to a larger radius.” is incompatible
with your OP question “ … , what would be the increase in velocity/speed? ”.

You are using scientific terms in inapplicable ways. That makes for total confusion.
You need to describe the physical system more completely.

• Bandit127
You can calculate the moment of inertia of your object, and the kinetic energy as function of its speed follows from that. You have the initial energy, and you increase this by 20 pounds * 1 foot, so you know the new energy, which you can convert back to angular velocity.

You should consider using SI units, as imperial units are just a huge mess if you want to calculate anything.
Thanks for that. I am sure you are right about SI units. My goal was just to see if I could get a hard number for mps or fps or rpm that resulted from the energy input to the vertical rotation. Assuming 180 rpm of original speed . (I added downstroke to imply vertical rotation). My degree is in Communications, (Graduated with Honors). I am much better with words than numbers, although Baluncore is correct that I made quite a few errors in my statement of the problem, including the OP Question. Currently, I am going through a health condition that reduces my cognitive skills. Originally, I attempted to become an Engineer but I quickly learned I am incapable of doing the math. This is one of the few places I can go with help on my inventions when I get stopped by the math. I, literally, would not have a clue as to do what you suggest, even though it is obviously the way to go. Let me know if you know of anywhere I can get something like this calculated, even if it is for a fee. Just need to keep it reasonable. Thanks.