- #1

Ocata

- 198

- 5

Hello,

I'm trying to reconcile what seems to me to be a contradiction.

Last week, I did a lab experiment where we stacked some metal bars in a tray and measured the force required to pull the tray into motion and break away from the force of static friction. As we predicted, the more mass we placed in the tray, the more force was required to move the tray. So clearly, to me, as you increase the mass, you increase the weight, thus you increase the normal force, and so force of static friction increases since Fn(mue) = Force of Friction, which means the force required to pull the tray to overcome Fn increases as mass increases. I hope this is correct (or else I'll have to redo my lab report).

However, now that I'm learning about centripetal acceleration I'm going back to the linear static friction lesson from last week and wondering why the formula seems to lead to the masses cancelling out:

[itex][F_{net} = ma] = [F_{friction} = ma] = [μ(F_{N}) = ma] = [μ(F_{G}) = ma] = [μ(mg) = ma]

[μ(g) = a][/itex]

In our lab, we used one surface type. So μ remained constant. We calculated the weight of the cart using the same constant for gravity, 9.8m/s^2.

I definitely felt that has we added weight to the cart, I had to pull with more and more force to break the cart into motion. So why now that I'm learning about centripetal force am I learning that m actually cancels out of the equation?

If mass definitely has an effect on the frictional force, then why does it cancel out of the equation and why is said not to be a factor?

I'm trying to reconcile what seems to me to be a contradiction.

Last week, I did a lab experiment where we stacked some metal bars in a tray and measured the force required to pull the tray into motion and break away from the force of static friction. As we predicted, the more mass we placed in the tray, the more force was required to move the tray. So clearly, to me, as you increase the mass, you increase the weight, thus you increase the normal force, and so force of static friction increases since Fn(mue) = Force of Friction, which means the force required to pull the tray to overcome Fn increases as mass increases. I hope this is correct (or else I'll have to redo my lab report).

However, now that I'm learning about centripetal acceleration I'm going back to the linear static friction lesson from last week and wondering why the formula seems to lead to the masses cancelling out:

[itex][F_{net} = ma] = [F_{friction} = ma] = [μ(F_{N}) = ma] = [μ(F_{G}) = ma] = [μ(mg) = ma]

[μ(g) = a][/itex]

In our lab, we used one surface type. So μ remained constant. We calculated the weight of the cart using the same constant for gravity, 9.8m/s^2.

I definitely felt that has we added weight to the cart, I had to pull with more and more force to break the cart into motion. So why now that I'm learning about centripetal force am I learning that m actually cancels out of the equation?

If mass definitely has an effect on the frictional force, then why does it cancel out of the equation and why is said not to be a factor?

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