# Centripedal acceleration

1. Nov 18, 2014

### Sam Smith

I am curious, when you are swinging your arms back and forth whilst holding a glass of water as you would with a pendulum would it experience centripedal acceleration? I would assume that it would?

2. Nov 18, 2014

### jbriggs444

Yes. It will experience centripetal acceleration. At the bottom of the swing when your hands are at the greatest velocity, the centripetal acceleration will be greatest. At the top of the swing when your hands come to momentary rest, the centripetal acceleration will be momentarily zero.

Of course there will be back and forth tangential acceleration as well. The water may slosh in the glass.

3. Nov 18, 2014

### A.T.

To move on a circle arc, it must undergo centripetal acceleration.

4. Nov 18, 2014

### Sam Smith

Yes what is confusing me is that centripedal acceleration = velocity^2/Radius
if you then wnated to use velocity reading in the x direction and centripedal acceleration to find radius ie Velocity^2/centripedal acceleration then the radius would change how can I find the accurate reading for the radius?

5. Nov 18, 2014

### A.T.

You have to use the tangential velocity (perpendicular to radius).

6. Nov 18, 2014

### Sam Smith

I am using that value at various points along the pendulum's path and I am also using the centripedal acceleration at the same points along the pendulum however my values for radius are changing and are not what I would be expecting

7. Nov 18, 2014

### A.T.

How did you get it?

If your radius is constant, just measure it with a ruler. The centripetal acceleration must change not the radius.

8. Nov 18, 2014

### Sam Smith

Yes I have measured with a ruler but if everything is working correctly the above equation should give me the correct value but it doesnt. At the moment I have decided to take the value where velocity is at the greatest so I have taken this instaneous value .^2/acceleration at this angle however, the two values dont match

9. Nov 18, 2014

### A.T.

Again, where did you get the acceleration value from?