# Trying to figure out the forces needed to push a heavy sliding door.

## Main Question or Discussion Point

I have been working with Physics for a while. I have recently come across a problem I could not solve efficiently. I have been designing a sliding door with 4 wheels with a rolling co efficient of 0.03. I thought that if I simply be using Force applied by door on all 4 wheels multiplied by friction I could find the force needed to push the door. However I just want to know if there are any other important factors I need to take into account (Im not sure how to incorporate Inertia)

## Answers and Replies

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Well, if the door is initially still...you need to break this tendency of it to stay still...you need to apply a force to accelerate the door (F=ma) from v=0 to some reasonable speed v=v1 at which point (if you need to continue to open the door more) you can maintain such speed for a few more inches (at F=0.03*...) and THEN let go...

So, it all depends how quickly you want to open the door..you can accelerate at various rates...

BruceW
Homework Helper
Yes, there will be some energy required for inertia. But this is pretty small. Only 1/2mv^2, and v is going to be pretty small, so the energy required to overcome inertia is very small.

While the door is moving, the biggest energy loss is probably rolling friction. But the door will probably also require guides on the ceiling, so that the door doesn't move to the side. The friction between the door and these guides will also cause energy loss. By guides, I mean like grooves attached to the ceiling.

When you start to move the door from rest, you will notice it seems to take more force than when the door is already moving. This will be due to the wheels having sunk very slightly more into the floor, making it hard to move the door at first.

You can also approximate such a force via FT = mv assuming the force is a fixed value.
For more, see IMPULSE in wikipedia for example...

http://en.wikipedia.org/wiki/Impulse_(physics [Broken])

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