# Movement of a plank

Gold Member
Here is a plank in empty space(There are no forces except one) .Someone is pushing it on a side.Will it rotate or Move straight in the direction of the force?

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Doc Al
Mentor
Here is a plank in empty space(There are no forces except one) .Someone is pushing it on a side.Will it rotate or Move straight in the direction of the force?
What do you think? Apply Newton's 2nd law for translation and for rotation.

Gold Member
What do you think? Apply Newton's 2nd law for translation and for rotation.
I don't quite understand that.

WannabeNewton
Write down ##F = ma## and ##\tau = I\alpha## for the system you drew.

Gold Member
Write down ##F = ma## and ##\tau = I\alpha## for the system you drew.
OMG!What's ##\tau = I\alpha## ?

Nugatory
Mentor
OMG!What's ##\tau = I\alpha## ?

Something that doesn't easily hit in google :)
Try googling for "moment of inertia" and "torque"

Gold Member
I have not heard about anything about the moment of inertia or angular acceleration.Anyways,The plank will rotate,Am I right?

Doc Al
Mentor
I have not heard about anything about the moment of inertia or angular acceleration.Anyways,The plank will rotate,Am I right?
The motion of the plank will be a combination of the translation of the center of mass plus rotation about the center of mass. It will rotate as well as translate.

Gold Member
The motion of the plank will be a combination of the translation of the center of mass plus rotation about the center of mass. It will rotate as well as translate.
Then where should I apply a force so the plank will only move straight without rotating?On the center of Mass?

Doc Al
Mentor
Then where should I apply a force so the plank will only move straight without rotating?On the center of Mass?
Yes, at the center of mass.

1 person
Gold Member
When I apply the force on the sides it will rotate and translate,What will happen if I remove the force.Will the plank keep rotating and translating or Move in a constant velocity in a straight line?

Doc Al
Mentor
When I apply the force on the sides it will rotate and translate,What will happen if I remove the force.Will the plank keep rotating and translating or Move in a constant velocity in a straight line?
When you remove the force, the center of mass will continue moving in a straight line at constant speed. And the plank will continue to rotate about its center of mass with a constant angular velocity.

Gold Member
Thank you So much Doc Al