# Serious problem with centripetal force

1. Dec 3, 2013

### Prometium

1. The problem statement, all variables and given/known data

The soluble problem We have a disc, horisontal, which is rotating 0.5 revolutions per second. A block is placed on this disc with the mass 0.6 kg and 0.2 meters from the shaft. First, I convert 0.5 rates per second to T = 2 seconds. w = 2∏/2 --> w = ∏ --> m = 0.6 kg --> r = 0.2 meters

Fc = (0.6)(0.2)(∏)^2 --> Fc = 1.184352528 N --> Fc = 1.2 N

This is correct according to facit. So easy, but I just wanted to show how different this is in comparism to the coming one.

The insoluble problem A carousel, where the distance between centre and attachment to chain is 0.8 meters, the chain is 1.0 meter long and weight in the chain 1.0 kg. T = 4.0 s. Now, centripetal forces is asked, and I do the same as above: w = 2∏/4 --> w = ∏/2

Fc = (1.0)(0.8)(∏/2)^2 --> Fc = 1.97392088 N

This is according wrong according to:

http://www.walter-fendt.de/ph14d/karussell.htm

Even though the latter is hanging in a chain, the horizontal force should be the same; but resulting different. In Walter Fendt, they have found out that the radius is 1.06 m (0.8 + 0.26). The angle is unknown, but they have through 0.26 m counted this: sin a = 0.26/1.00 --> a = 15.

2. Relevant equations

Fc = mrw^2

w = 2∏/T

What have I missed?

Last edited: Dec 3, 2013
2. Dec 3, 2013

### SteamKing

Staff Emeritus
What does 'rates per second' mean? Is it supposed to be 'radians per second' or 'revolutions per second'?

3. Dec 3, 2013

### Prometium

It was supposed to mean "revolutions per seconds". In fact, I have always believed that RPM on the motorcycle and cars meant rate per minute, but I did just learn that it means revolutions per minute. English is my second language.