Question

1. Try this, if you haven't before: Place your finger tightly over the top of the straw, and lift the straw up out of the water. You should find that the water stays in the straw. a. What is the net force on the water in the straw? b. Draw a free body diagram for a system that is the water. c. Is the gas pressure inside the straw, between the liquid and your finger, greater than, less than, or equal to atmospheric pressure? Explain. d. If your answer to part c was ''greater'' or ''less,'' how did the pressure change from the atmospheric pressure to the final pressure? [Since this is a prediction, you will not be graded on accuracy. However, you still need to write down your thoughts to get credit. By the end of the lab, you should be able to answer this question.]

Answer 1

Parte b) previous image

Parte a) Net forces acting on the system are the weight and pressure on the bottom of the vessel containing the liquid multiplied by the area of the transversal section of the container.

Parte c) The pressure between the finger and the liquid is less than atmospheric pressure, as was demonstrated by Torricelli, who concluded that the pressure of the atmosphere is due to the weight of air.
Their experiment involved placing a tube with mercury and one of the ends sealed, I note that the liquid reached 760mm, leaving the sealed end and the liquid, the same way one espacientre the finger and our liquid. In like manner, the empty space was called, and the pressure at this point is almost zero, since it is impossible to recreate the absolute vacuum, but if you can create a space with a small amount of matter such as ours. Therefore it is demonstrated that the pressure is less than atmospheric.

Parte d) The pressure has a certain value to zero. as decreases? Once the finger is placed on top of the pipe or container, air particles that are putting pressure on the space (atmospheric pressure) are no longer in contact, and begins a process of reduction of particles in that space, occur phase change process, some particles decrease their height and begin to form mixtures of liquid and particles, thus reducing particle to exist in a given space without the addition of new, think what you are as empty and coloce vacuum pressure is zero.