# Accelerometer via ball on string

#### andrewr0x

How would I go about measuring forward acceleration using a free-swinging ball on a stand? Could anyone post a free body diagram or an equation that might describe this?

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#### robphy

Homework Helper
Gold Member
Two external forces on the ball:
downward gravitational force with magnitude (mg)
tension tangent to the the rope (T)

Compute net-force vectorially.

Use Netwon II.
Solve for the acceleration (a) as a function of angle (theta) with respect to the vertical.

#### andrewr0x

Would tan(theta)=a/g ?

#### Doc Al

Mentor
andrewr0x said:
Would tan(theta)=a/g ?
That's right. (Where theta is the angle the string makes with the vertical.)

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