Remember when we learned about WORK and the balance in FORCE and DISTANCE in any machine to do this work. Well, Hydraulic and Pneumatic systems are not excluded from this idea. Fluid systems such as Hydraulic and Pneumatic systems are also machines that can either give a FORCE or a DISTANCE advantage or disadvantage. To understand how this works, think about the idea of PRESSURE in a fluid while you watch this video below.
Pressure in a BottleThe pressure exerted or forced on to the different holes caused the water projecting out into the bucket to shoot out at different distances. This can be connected to the formula P=F/A. The amount of water sitting above each hole is the amount of force pushing down on each hole. The amount of water sitting above hole A is less than hole C, therefore the FORCE (N) of water pushing down at hole A is less than hole C. Now, since the AREA of the holes are the same, and the area of the water bottle is the same, we can say that the AREA remains the same. EG. Hole A: 2N of water divided by 1cm2 area. This would equal 2N/cm2. Hole B: 4N of water divided by 1cm2 area. Equalling 4N/cm2 Hole C: 6 N of water divided by 1 cm2 area. Equalling 6N/cm2 The following video is similar to what we did in class..... In a previous class you did an activity that showed you a physical difference between hydraulic and pneumatic systems. Primarily that systems with liquids are INCOMPRESSIBLE OR NON-ELASTIC, and systems with gasses (air) are COMPRESSIBLE, AND ELASTIC. Now try connecting two syringes with a plastic tube. Follow my instructions to fill with air first, then water. Observe the differences in movement. The video below shows you how you could build a device that is automated by enclosed fluid power. In this case, the student chose WATER as the fluid. You could also use AIR. In a Hydraulic system, OIL is often used. Can you think of a reason why oil instead of water could be used? Okay, so I couldn't find part 2 of this video series. Instead here is a fun video that at very least, gives you examples of pneumatic systems and a little more.... Now, with this information, you can start to fill in the PNI chart provided. =) Let's revisit the idea of the floating plasticine. When we did this experiment we talked about PRESSURE and how changing the surface area of the plasticine's shape could effectively reduce the downward force of the plasticine's weight allowing the 'boat' to be buoyant in water, as well to hold a load. To go a step further, see how DENSITY is connected to this idea in the following tutorial: Note that they use pounds instead of grams or Newtons. The idea is still the same so not to worry about converting the scale; however, if you need to know .... 1 pound = 454g = 4.5N) At your table, discuss why you think the egg was buoyant in one jar, but not in the other. Could you think of a way the egg can be neutrally buoyant (floating in the middle)? BUOYANCY is the tendency to rise or float in a liquid or gas. Buoyancy is a force that opposes Gravitational force, pushing matter upwards, against gravity. This is called a BUOYANT FORCE. DENSITY is the amount of mass in a certain unit volume of a substance. The formula for density is: D = grams/ml If the density of an object is lower than the density of the liquid or gas it is in, the object will be buoyant. If the density of the object is higher than the density of the liquid or gas it is in, the object will NOT be buoyant, the object will sink. In the Science Power 8 Text, p141 has a table that shows the densities of some familiar matter
PRESSURE Compare these two scenarios: A: You use 10N of force to push a nail into a balloon. B: You use 10N of force to push the palm of your hand into a balloon. How are these two scenarios different? How are they the same? WHY?? Pressure is the amount of force applied to a specific area. P = Force / Area This is otherwise calculated as P = Newtons / cm2(squared) or in more practical terms P = pounds/square inch (PSI)
Viscosity is a fluid's resistance to FLOW. That means that if a fluid is VISCOUS, it flows slowly. Likewise, if a fluid is not viscous, it flows quickly. From the lab, order the fluids you used and rank them from most viscous to least viscous. QUESTION: How could we change the viscosity of a fluid? Explain using the particle theory how this might work. Watch the video below. It may help answer the questions above. Note: When they talk about MOLECULAR bonds, they are talking about PARTICLE attraction (Particle Theory). The definition of a fluid is anything that FLOWS. Water can flow out of a container. It is a fluid. Sugar can also flow out of a container. Is sugar also a fluid? At the molecular / particle level, the answer is NO. Reason is because the particles in sugar are not free to move around each other. They are in a fixed position, like in all other solids. They therefore, do not have the same properties of fluids.
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