# Circular motion vertical force

1. Jun 11, 2014

### ramanakumars

Hi everyone,
If you have a horizontal circular motion (with gravity action on the object), what holds the object up in the horizontal plane? All vertical components of the tension go to zero when the angle with the vertical axis is 90°... Where am I going wrong?

Thanks

Ramana

2. Jun 11, 2014

### jbriggs444

Why would the angle with the vertical axis be 90° rather than something a bit less than that?

3. Jun 12, 2014

### ramanakumars

Do you mean to say that even theoretically, you cannot have an object in uniform circular motion completely with the attached string completely horizontal?

4. Jun 12, 2014

### jbriggs444

Right. For the reason that you are pointing out. If the string were horizontal, there would be no vertical component of force.

5. Jun 12, 2014

### mattt

In that case, the force the string exerts on the body is horizontal, so there must be another force that compensates the weight force. If the body is doing its horizontal uniform circular motion sliding on horizantal ground, then it is the normal (support) force that compensates the weight.

If the body is doing its horizontal uniform circular motion above ground, and there is no other force acting on the body (just the weight and the tension of the string), then the string can not be totally horizontal.

6. Jun 12, 2014

### ramanakumars

I see... Thanks for clearing that up guys! Makes perfect sense!