The role of surface tension in the formation of drops is described. Surface tension can be measured by using a suitable needle and dripping a liquid from it. Measurements made with simple apparatus are found to agree well with literature data.
I describe an experiment involving the moka Italian coffee pot. The pot is an ingenious device for making coffee that uses the liquid-vapor equation of state of the water and Darcy’s law of linear filtration. The filtration coefficient of coffee is measured and a steam engine model is used to estimate the efficiency of the coffee pot.
Archimedes' principle is one of the fundamental themes of the mechanics of fluids in high school; it is described in detail in any introductory physics textbook1 and it asserts that “a body immersed, or partially immersed, in a fluid receives an upward force equal to the weight of the fluid it displaces.” In mathematical terms, Fup = ρgVx, where ρ is the fluid density, g the free-fall acceleration, and Vx the volume of the immersed portion of the body. In a partially immersed body, the fluid exerts pressure on all surfaces of the body, laterally and on the bottom [Fig. 1(a)]. Notice that the forces on the sides cancel by symmetry and the net effect of the fluid pressure is an upward buoyant force. Likewise, if the body is totally immersed [Fig. 1(b)], the fluid also exerts pressure on the top of the body, but since the pressure on the bottom will be greater than on the top (pressure increases linearly with depth in a fluid of uniform density), the result is a net upward buoyant force.
This paper describes an experiment on uniform circular motion, carried out in a second year class of the High School ‘E. Fermi’ of Ragusa (Sicily/Italy), employing an old turntable and a smartphone using the phyphox app. Data analysis allowed us to confirm that the motion is maintained uniform for all three nominal values of the turntable frequencies. We were also able to measure angular accelerations, in both the switch on and final stop phases. Thanks to the easy availability of the equipment used, the activity can also be proposed as Hands up teaching, to be carried out during extracurricular hours in either single or group work.
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