pressure Flashcards
(17 cards)
what is pressure?
pressure is the force acting per unit area
what is the formula for pressure?
P = F/ A
what is the SI unit of pressure?
N/m2 or Pa
what is the relationship between pressure, force and area?
From the relationship between pressure, force and area, we can see that:
• the greater the magnitude of the force, the greater the pressure; and
• the smaller the contact area, the larger the pressure.
what is a hydraulic press?
a hydraulic press has two pistons at each of its two ends, where one of these pistons has a larger SA than other
what is pascal’s law?
if a pressure is applied to an enclosed liquid, the pressure transmitted to all other parts of the liquid undiminished
what is density?
density is defined as mass per unit volume
Density is used to identify substances or the purity of substances. For example, the density of pure gold is 19.3 g/cm.
(If a gold necklace has a different density from that of pure gold, it is not made of pure gold.)
Substances that are less dense than water will float on water. Substances that are denser than water will sink in water.
what is the formula for density?
p = m(kg) / v (m3)
what is the SI unit for density?
kg/m3
what are the steps to determine the density of a liquid?
1 Weigh an empty graduated measuring cylinder.
2 Pour the liquid into the measuring cylinder and weigh both the measuring cylinder and the liquid.
3 Determine the mass of the liquid by subtracting the reading in step 1 from the reading in step 2.
4 The volume of the liquid can be measured using the measuring cylinder.
5 The density of the liquid can be calculated using: Density of liquid = mass of liquid
volume of liquid
what are the steps to determine the density of solids?
need to measure its mass and volume:
The mass of the solid can be measured using an electronic balance.
The volume of an irregular solid can be found by immersing the solid in water and measuring the volume of water displaced, and then taking the difference between the readings
The volume of regular solids, such as a cuboid or a cylinder, can be calculated using measurements made by measuring instruments and applying appropriate geometric formulae.
what is the formula for measuring pressure in a liquid?
pressure at a certain depth/between two levels in a liquid =
P = hdg (height x density x gravitational field strength)
what are the factors affecting pressure at a given depth beneath liquid surface in a liquid?
depth (since d and g remains the same)
NOT SHAPE OF CONTAINER / NOT THE VOLUME OR CROSS SECTIONAL AREA OF THE LIQUID
in a container with different tubes, the liquid level will be at the same height regardless of the shape of the tubes, and so the water pressure will be the same
if the height of the liquid level is not the same, there will be a net force which will result in pressure differences and cause the liquid levels to rise or fall
what is a mercury barometer?
used to measure atmospheric pressure
a glass tube is filled completely with mercury, which is inverted into a trough containing mercury.
some mercury flows out from the tube into the trough, while most of the mercury remains in the tube.
The space above point A is a vacuum. Thus, the pressure at A (Pa) is zero.
Thus, the pressure at B, which is level with the surface of the mercury in the trough, is the same as the atmospheric pressure, hence Pb - Pa=hpg
point c is where atmospheric pressure is acting on the mercury Pc which is the same as Pb, so finding the pressure at Pb can give the atmospheric pressure since the pressure at the same level in a fluid is the same.
what is a manometer?
used to measure gas pressure - Pb - Patm = hpg
The liquid at A is exposed to the atmosphere. Thus, the pressure Pa at A is the atmospheric pressure Patm.
When the gas supply is turned on, the gas will exert pressure Pg on the liquid at B.
As Pg is higher than the atmospheric pressure, the liquid at A will rise until the pressure Pc at C, which is on the same horizontal level as B, equals the gas pressure. The pressure Pc at C is given by Pc- Pa = hpg.
Since Pc = Pb and Pa = Patm,
Pb - Patm = hpg
Pb = hpg + Patm
how is pressure transmitted equally to all parts of an enclosed liquid?
a force (F1) is applied on the smaller piston, resulting in a pressure exerted, on piston 1 and hence the liquid, which is given P1= F1/A1
as a liquid cannot be compressed, the pressure P1 would be transmitted equally to the other parts of the liquid and to piston 2. hence, the pressure exerted on piston 2 is P1 = F2/A2, and the force on piston 2, F2 = F1 * A2/A1
what is the multiplier effect of hydraulic presses?
F2 = F1 * A2/A1
F2 is a multiple of F1. (The multiple is given by the ratio of the areas A2 to A1.) Thus, a hydraulic press has a multiplier effect (proportional increase). It converts a relatively small force F1 on a small piston into a relatively large force F2 on a large piston.
