# Homework Help: Centripetal force

1. Nov 23, 2004

### UrbanXrisis

in uniform centipetal motion, the centipetal accleration points towards the center, what about the centipetal force? What direction does this force point?

2. Nov 23, 2004

### bjr_jyd15

Acceleration is always in the direction of the unbalanced force. The centrifugal force (inertia) wants the motion to continue its direction at any given moment. However, the centripetal force keeps the motion and force towards the center.

3. Nov 23, 2004

### UrbanXrisis

so the centripetal force acts towards the center too?

4. Nov 23, 2004

### Staff: Mentor

Of course. As you noted, an object in uniform circular motion is centripetally accelerated. And, by Newton's 2nd law ($\vec{F} = m\vec{a}$), the net force and acceleration point in the same direction: towards the center.

By the way, the word "centripetal" means "towards the center".

5. Nov 23, 2004

### UrbanXrisis

So if I was twriling a ball connected to a spring scale. And there was enough air friction to make the net force=0. Then what would be the relationship between the force the spring scale reads vs the centripetal force?

6. Nov 24, 2004

### Staff: Mentor

If the net force were zero, then the ball would not be twirling in a circle. For the ball to move in a circle, there must be a non-zero net force on it; if the ball is moving at a constant speed, then that net force must point towards the center of the circle.

If you twirl a ball connected to a spring scale, then the spring scale reads the tension you are exerting on the ball. The component of that force acting towards the center will contribute to the centripetal force. (But other forces, such as gravity, may also contribute to the centripetal force.)