# Grade 11 Physics Lab Report

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10.28 Fill a plastic cup to the very top with water. Put a piece of paper on top of the cup so that the paper covers the cup at the edges and is not much bigger that the surface of the cup. Turn the cup and paper upside down (practice over the sink first) and hold the bottom of the cup (now on the top). Why doesn't the water fall out of the cup? The downward pressure on the paper by the water inside the cup is less than the upward pressure exerted by the air outside. This occurs because the pocket of space between the bottom (top of inverted glass) and the surface of the water has low pressure compared to the atmospheric pressure exerting an upward force on the piece of paper. The molecules of air that are trapped into the glass by the piece…show more content…
The buoyant force is the upward force on the object is the sum of the forces (PA) at the top and bottom of the block: P_1 A-P_2 A=ρgΔhA  FFonO=ρgV. The sum of the upward force from your arms (or other lifting apparatus) and the upward buoyant force will be much greater than the downward force from the fluid (exerted at the top of the object). 10.32 When placed in a lake, an object either floats on the surface or sinks. It does not float at some intermediate location between the surface and the bottom of the lake. However, a weather balloon floats at some intermediate distance between Earth's surface and the top of its atmosphere. Explain. A floating object that is fully submerged in the fluid is in the state of neutral buoyancy, where the mass of the object is precisely equal to the mass of the fluid it displaces. For an object that’s dropped into the lake, it will either sink or float, depending on whether its density is greater or less than 1000 kg/mg3. On the other hand, for a weather balloon filled with hydrogen or helium, as it rises to higher altitude it will expand due to a lower atmospheric