# Net force acting on a piston shaft of an actuator

1. Nov 14, 2015

### rajdeep1

1. The problem statement, all variables and given/known data
A cylindrical piston shaft weighs 250 g and is held vertically inside an actuator (We can assume actuator is a box with hollow cylindrical space to fit the piston shaft). Compressed air at 100 psi is supplied at the bottom of the actuator and is acting on the piston upwards with a force of 90 N. The coefficient of friction between the piston shaft and the inside wall of the actuator is 0.61. I need to calculate the speed by which the shaft will eject and shoot upwards from the actuator.

2. Relevant equations
Net Force= ma
d= ui*t+ 0.5*a*t^2

3. The attempt at a solution
Net Force= 90N- 0.25*9.81 - Ff (I am not sure if this is the right way to calculate the net force. Also, not sure how to calculate the frictional force here, although I do know Ff= coeff* R)

Assuming I have a net force, I can easily find the acceleration and the distance it travels in a second.

Thank you so much.

2. Nov 15, 2015

### haruspex

Is this a textbook question or a lab? There is not enough information. You will certainly need to know the length of the actuator.
The coefficient of friction doesn't help with no way to determine the normal force.

3. Nov 15, 2015

### rajdeep1

It is not a textbook question, it is more of a lab question. The length of the actuator is 10 inch.
Is there any other information that we need?
Thank you.

4. Nov 15, 2015

### haruspex

As I wrote, the coefficient of friction is no help since there is no obvious way to find the normal force between piston and cylinder. It would be more helpful simply to measure the frictional force.

5. Nov 15, 2015

### rajdeep1

Thank you. Could you please tell me the ways to measure the frictional force then?

6. Nov 15, 2015

### haruspex

By direct experiment.