# I Actuator on an accelerating body

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1. Apr 5, 2017

### arjunzv8

Hello all, new member here. Signed up cause I am stumped by a physics problem.

I am trying to size a linear actuator. Basically I have a large body that is accelerating at acceleration in x direction. I have a linear actuator aligned in the x direction that is rigidly attached to the large body on one end and the other end is touching a box. The actuator has to hold the box (mass m) in place relative to the large body.

If the large body is accelerating at "a" till it reaches velocity "v", what is the power requirement of the actuator. For simplicity, I am ignoring air drag, actuator efficiency etc.

Attached image shows the setup.

Is this a non-inertial frame?
Is the actuator consuming power even if there is no motion (relative between actuator and box) because of the inertia of the box?
Is it correct if I calculate power requirement as shown below?
F=ma
Distance d=0.5*a*t^2
Time t=v/a
Power P=F*d/t

Since I am ignoring air drag, power is consumed only during acceleration correct?

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2. Apr 5, 2017

### A.T.

If you ignore actuator efficiency, then no power is required. You could replace the actuator with a rigid attachment which also consumes no power.

3. Apr 5, 2017

### arjunzv8

I am still confused by this. Unlike a rigid attachment, an actuator would still consume power to remain in position as long as there is a load (here that is F=ma during the acceleration). So how would I then calculate this power requirement.

4. Apr 5, 2017

### A.T.

From the technical specifications of the actuator. Ideally you would use one, that can be locked in a static position without power consumption.