# Does friction torque in speeding up = speeding down?

#### Anak Soleh

Homework Statement
'm trying to calculate moment of inertia of a pulley connected to a shaft mounted on bearing by using free fall method. A load (270 g) is tied to a string and the string is wrapped around pulley.
The load is dropped from 1,6 m height then i measure rotation speed of pulley when the load is going down, plot the data and get acceleration from the slope (α up). I also measure rotation speed after the load is already on the ground until it is stopped and get the deceleration (α down).
Homework Equations
Στ=Iα
On speeding up:

τload - τfriction = Iαup

On speeding down:

τfriction = Iαdown

If i substitute τfriction from speeding down to speeding up equation, i get moment of inertia:

I = (τload)/(αup+αdown)

But, is this allowed? Does friction torque in speeding up is equal to friction torque in speeding down?

Additional info: the speeding up range from 0 to 38 rad/s and the speeding down from 38 rad/s to 0 rad/s.

#### Attachments

• 14.6 KB Views: 12
Last edited:
Related Introductory Physics Homework Help News on Phys.org

#### haruspex

Science Advisor
Homework Helper
Gold Member
2018 Award
Does friction torque in speeding up is equal to torque in speedingdown?
It's a reasonable assumption.

#### Anak Soleh

It's a reasonable assumption.
Thanks. That's assuring.

### Want to reply to this thread?

"Does friction torque in speeding up = speeding down?"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving