Question

Is it possible to open a pen cap with one finger? Why?

Answer 1

If we have to open a pen cap then we have to apply some force to the pen and some to the cap which means we have to apply two forces which will be opposite to each direction.

Complete step by step answer:
To understand the concept behind the answer to this question we must first know what force and torque are and how do they work.
When two objects interact with each other and result in a push or pull, then this push or pull on the object is force. For example, when a bat hits a ball there is the force on the ball produced by the bat. As a result of force, any object can start moving or any object can be on rest. The measurement of the movement in an object due to force is known as torque.
Now, coming back to the question if we will try to remove the pen of the cap using one finger then it will only provide one force. As discussed above how we have to provide two forces for opening a cap, this requirement will not be fulfilled, and we will not be able to open the cap of the pen successfully.

Hence, we can say that it is impossible to have a pen cap removed from it using one finger.

Note:
The reason that we have mentioned in the question that two forces will be required to remove the cap from the pen is that this is the only way that we can achieve the required torque which will deal with the friction which is between the pen and it’s the cap.