05 Pressure and Density Flashcards
Define density
the mass per unit volume
How do you measure volume accurately when using a measuring cylinder?
Read the volume at eye level and to the bottom of the meniscus
place measuring cylinder on a level surface
What is the unit for density?
g/cm3 or kg/m3
Which orientation of the block below would create in a smaller pressure on a table?
First orientation
P = F/A
The second block has a larger area in contact with the table, for the same force, therefore, the pressure is lower
How can the volume of an irregular object be found using a measuring cylinder?
- Half fill measuring cylinder with water and read initial volume at eye level and bottom of the meniscus
- lower object into measuring cylinder- make sure that it is fully submerged and water level has not risen above the scale
- read final volume at eye level and bottom of the meniscus
- Volume of object = final volume - initial volume
The second object has half the mass but the same volume, How does its density compare to the first object?
density = mass / volume
if mass is double for the same volume, the density doubles.
density is proportional to mass
How could you find the density of a paperclip accurately?
- measure the mass of 50 paperclips on a balance
- half fill a measuring cylinder with water and record initial volume
- carefully add 50 paperclips and record final volume.
- calculate the volume by taking the difference
- Find density = mass / volume
What is a pascal?
1 Pascal = 1 Newton per metre square
How do you find the density from a mass vs volume graph?
calculate the gradient
gradient = rise/run = mass/volume
Explain what design feature makes a knife able to cut easily.
A sharp knife with a small surface area creates a greater pressure for the same force.
pressure = force/area
The knife will cut more easily
What equation links density, mass and volume?
What is the unit for force?
Newton or N
Camels have adapted to walk effortlessly in the desert sand. Explain
Camels feet have a large surface area
P = F/A
A larger surface area for the same force results in lower pressure
The camel will not sink as much in the sand and can walk more easily.
How can the volume of an irregular object be measured accurately using a Eureka can?
- overfill eureka can with water and wait for water to stop dripping from the spout
- hang object from a string and slowly lower the object into the water
- make sure that the object is fully submerged
Which orientation of the block below would create a larger pressure on a table?
Second orientation
P = F/A
The second block has a smaller area in contact with the table for the same force, therefore, the pressure is higher
What is the unit for volume?
m3
If a block of wood is cut in half, how does the density of the original block compare with the new half blocks?
Their densities are the same.
Both the mass and the volume were halved.
Which dam must withstand a larger pressure?
The dam on the right. It has a greater depth (h) and so the pressure on the dam will be greater.
Static liquid pressure does not depend on the volume of the liquid - but its depth.
What is the unit for pressure?
Pascal (Pa)
What is the equation that links pressure, density of a fluid, gravity and depth?
Which section A, B, C, D or E experiences the largest pressure?
P = density x gravity x depth
All the sesctions experience the same pressure since the depth of water is the same.
Pressure at depth is not affected by the volume of water- only the depth of water above it.
How does the density vary between ice and sea water?
Ice has less particles per unit volume
ice has a lower density
Ice floats on sea water
How can mass be measured accurately?
- placed balance on level surface
- tare (zero) balance before use
How does the pressure vary with depth in the ocean?
As depth double, pressure doubles.
Pressure is proportional to depth
The graph is a straight line through the origin.
What is the unit for mass?
kg
always convert grams to kilograms
Fluid pressure acts in all directions.
What causes air pressure?
Air particles move in all directions and collide with objects
Air particles move fast and freely
Air pressure is related to the depth of air over the object.
What is the unit for area?
m2 or cm2
What equation links pressure, force and area?
Which object (a or b) has the largest density?
Object a
It has more mass per unit volume - the gradient is steeper
Which object below would have the highest density values?
First object
Greater mass per unit volume
The particles are more closely packed
