- #1

- 1

- 0

## Main Question or Discussion Point

Hello:

I have quite a few questions regarding objects free falling and the forces that they generate. I have been doing some reading on this topic over the last few days but I think that I am missing some of the concepts and how they apply in the scenario that I am trying them to. I think perhaps the issue that I am running into is that I am not applying the fundamental concepts properly.

First, this is what I know, or at least I think I know: Force = Mass x Acceleration. Weight = Mass x g. Where G is the constant of 9.81m/s2. Now my questions based on this:

1. 'LBf', or pounds of force, is not the same as regular 'LB', pounds, correct? My understanding is that 'LBf' is a measure of Weight and 'LB' is a measure of mass, is this right?

2. I have seen several places refer to the units of Weight (in the equation I mentioned above) as 'LBf' (or pounds of force) and other places as 'N' (newtons). Which is it? This confused me since from what I have been reading 1LBf is equal to ~4.4N so the units can't be interchangeable, right?

3. All other things remaining the same, When calculating the force that a free falling object generates when it is suddenly stopped I tend to think that the equation Force=Mass x Acc will give me the answer. I use 9.81m/s2 as the acceleration since it is a free falling object thus falling at the same rate as anything else in the planet would, is my assumption correct?

4. This is where I start to get confused. If my assumption in the previous question is correct (which I am aware probably isnt), then that means that an object free falling at 1 meter would generate the same force as an object falling 2meters or even 100 meters. I know this isn't right but I am not sure how to prove that. Wha I'm I missing here? When do I bring the distance fallen into the equation?

Now to get specific. the reason I am trying to understand this is because I have a scenario that I am trying to get some data from. The scenario is the following.

I am standing 3 meters at the top of a hill and I am holding a 10 meter rope with both. The other end of the rope is tied to a 10kg dead weight which is already hanging 4 meters over the edge. This means that from where I am to where the load is there are 3 meters of rope laid out horizontally and 4 meters of rope dangling vertically over the edge for a total of 7m of rope past where I am holding. If I were to quickly let go of the rope and let 1meter of rope pay out before I grabbed it again what would be the force that I would feel at my hands when I grabbed that rope again? what if I let it go for 2m instead of 1?

For this scenario take into account that the rope is rated to a ridiculous strength and does not break, that the rope does not stretch, and that the load is stopped instantaneously meaning that I would be strong enough to not be moved forward when I grab the rope to stop the falling load. I know that this is not al all realistic since in a real system there would be some shock absorption from the rope and from me but for the sake of argument let say that there isn't. How can I use the formulas above to figure out the force generated at my end of the rope?

Thanks!

MG

I have quite a few questions regarding objects free falling and the forces that they generate. I have been doing some reading on this topic over the last few days but I think that I am missing some of the concepts and how they apply in the scenario that I am trying them to. I think perhaps the issue that I am running into is that I am not applying the fundamental concepts properly.

First, this is what I know, or at least I think I know: Force = Mass x Acceleration. Weight = Mass x g. Where G is the constant of 9.81m/s2. Now my questions based on this:

1. 'LBf', or pounds of force, is not the same as regular 'LB', pounds, correct? My understanding is that 'LBf' is a measure of Weight and 'LB' is a measure of mass, is this right?

2. I have seen several places refer to the units of Weight (in the equation I mentioned above) as 'LBf' (or pounds of force) and other places as 'N' (newtons). Which is it? This confused me since from what I have been reading 1LBf is equal to ~4.4N so the units can't be interchangeable, right?

3. All other things remaining the same, When calculating the force that a free falling object generates when it is suddenly stopped I tend to think that the equation Force=Mass x Acc will give me the answer. I use 9.81m/s2 as the acceleration since it is a free falling object thus falling at the same rate as anything else in the planet would, is my assumption correct?

4. This is where I start to get confused. If my assumption in the previous question is correct (which I am aware probably isnt), then that means that an object free falling at 1 meter would generate the same force as an object falling 2meters or even 100 meters. I know this isn't right but I am not sure how to prove that. Wha I'm I missing here? When do I bring the distance fallen into the equation?

Now to get specific. the reason I am trying to understand this is because I have a scenario that I am trying to get some data from. The scenario is the following.

I am standing 3 meters at the top of a hill and I am holding a 10 meter rope with both. The other end of the rope is tied to a 10kg dead weight which is already hanging 4 meters over the edge. This means that from where I am to where the load is there are 3 meters of rope laid out horizontally and 4 meters of rope dangling vertically over the edge for a total of 7m of rope past where I am holding. If I were to quickly let go of the rope and let 1meter of rope pay out before I grabbed it again what would be the force that I would feel at my hands when I grabbed that rope again? what if I let it go for 2m instead of 1?

For this scenario take into account that the rope is rated to a ridiculous strength and does not break, that the rope does not stretch, and that the load is stopped instantaneously meaning that I would be strong enough to not be moved forward when I grab the rope to stop the falling load. I know that this is not al all realistic since in a real system there would be some shock absorption from the rope and from me but for the sake of argument let say that there isn't. How can I use the formulas above to figure out the force generated at my end of the rope?

Thanks!

MG