Pressure Flashcards
Convert 1000 kg m^-3 to g cm^-3
1 g cm^-3
What is a characteristic of density of pure substance
The density of pure substance is unchanged, irrespective of the amount of substance
What happens when object is placed in liquid of same density
The object remains wherever it is released
What is the formula for pressure(non-liquid)
P = F/A where P can be in Nm^-2 or Pa. 1Pa = 1 Nm^-2
When a man is about to jump, why is pressure exerted on ground greater than pressure exerted when standing
In order for the man to accelerate upwards, normal reaction force exerted on the ground has to be larger than his weight. But when standing, his normal reaction force is equal to his weight
How to increase pressure
Increase the force or decrease the contact area
What is Pascal’s Principle
If external pressure is applied to enclosed fluid, pressure is transmitted equally to all other parts of the fluid
What 3 properties of liquids do hydraulic presses take advantage of
Liquids are incompressible
Pascal’s Principle(must state in full)
Liquid has no fixed shape, can fill up space in a container
What is the equation for force/surface area acting on the two pistons of a hydraulic press
F1/A1 = F2/A2
V1 = V2
Volume of liquid pushed by both pistons are equal
What is atmospheric pressure
Force due to molecular bombardment by energetic air molecules on us in all directions.
Atmospheric pressure drops by half every 5.6km(decrease w altitude)
Why do humans bleed at high altitudes
At higher altitudes, atmospheric pressure is lower, breathing is difficult and nose bleeding occurs as human’s large blood pressure bursts some blood vessels in nose due to difference in pressure
Why do aircrafts have pressurised cabins
Air pressure is at sufficient level to protect passengers and crew. Pressure is slightly lower than sea level to allow aircraft frame to be thinner and saves manufacturing and fuel cost
What happens when an object experiences a pressure difference
When there is difference in pressure exerted on opposite sides of rigid body, there will be net force which acts in direction of region of higher pressure to region of lower pressure
How do people suck through a straw
Sucking through a straw lowers air pressure in mouth/straw. Atmospheric pressure being larger than air pressure in straw, pushes on liquid surface. Pressure difference results in net force which pushes liquid up the straw and into the mouth
How does a suction cup work
When a suction cup is pressed against a wall, most of air underneath suction cap is squeezed out. This creates pressure difference between atmospheric pressure and trapped space under suction cup. Net force acts inwards on suction cup to hold it against a surface
What is equation for liquid pressure at certain depth
P = hpg
Explain why pressure in water at depth of 30m is very different from that at surface, but atmo pressure 30m below surface of earth is almost same at surface
Density of air under the surface is much lower than the density of water
How to find atmospheric pressure using mercury barometer
Height difference between top of mercury and mercury level in trough. Unit is cm Hg or mm Hg
What happens when liquid levels(same liquid) in two connected columns are not at same height
Pressure at base of right arm is higher than that of left arm. Liquid in horizontal section will experience net force to the left. Causes liquid to move to the left and equalise the water levels of the two arms
How to find difference in pressure using manometer
Difference in height of liquid in both arms
One arm of manometer connected to gas supply of higher pressure and other exposed to atmo pressure. What happens to height diff of liquid when
Atmo pressure increases
Density of liquid decreases
Diameter of U-tube decreases
More mercury poured into tube
Difference will decrease
Difference will increase
Difference remains the same
Difference remains the same
Explain whether a sealed empty bottle of dense material with cap will float or sink in water
It will float. As the density of air within the bottle has much lower density than water, the density of the empty bottle will be generally lower than that of the water and will float
Water in manometer is replaced with mercury. Explain the height difference between the two arms(one arm connected to gas source)
Height difference will decrease. A shorter column of denser liquid exerts the same pressure as a taller column of less dense liquid for the same pressure difference between both arms
