Topic 9 - Pressure and Surfaces Flashcards
How is pressure caused
-When objects exert forces on eachother , or when a fluid , (which can iether be a liquid or a gas ) exerts a force on an obect in contact with the fluid .
-The [ressure caused by any force ddepends on the area of contct on which the force acts , as well as the size of the force .
What is the unit of pressure
-Pressure is the force per unit area .
-The unit of pressure is the pascal , Pa, which is equal to one newton per square metre (Nm2)
pressure (Pa)+Force(N)/ Area a metres squared
Describe particles in a gas :
-Particles in a gas , are widely spaced ,a nd are moving rapidly .
-The particles are colliding with eachother and the walls o the container .
-When the particles collide with the 7 walls thehy exert a force .
-That force is acting t right angles to the wall (aka along the nromal ).
particles in a liquid ?
-Also exert a force at right angles to the walls of the container .
-Sccientists call all gases +liquids FLUIDS .
DO THE QUESTION ON SHEET :))
Describe the atmosphere .
-The atompshere is a thin layer of air around the EARTH .
-The atmosphere is most dense at the surface of the EARTH.
(THIS MEANS THAT THERE ARE THE GREATETS NUMBER OF MOLECULES IN A GIVEN VOLUME AT THE EARTH’S SURFACE .)
What happens as we increase the alititude ?
-The atmosphere gets less dense (Moves away from the surface of the Earth ).
-What is the pressure of the atmosphere caused by ?
-Air molecules colliding with a surface .
-As a sruface increases height baout ground level , the number of air molecules above the surface decreases .
-This means atmopshereic pressure decreses with an icrease in hieght .
SO , why do mountail climbers often take a supply of oxygen with them ?
-As the air pressure on the mountain may be TOO LOW , to uspply all the oxygen they need .
SO , why do crisp packets swel up in aeroplanes ?
-AT GROUND LEVEL , the air pressure inside the bag is the same as the air pressure outside the bag .
-However , when eroplanes are flying , the air pressure in the cabin , is kept at SLIGHTLY LOWER than the air pressure on the ground .
-This mens the air pressure inside the bag is GREATER than the air pressure in the cabin .
-CAUSING the bag to inflate
There is container with water .
-What will ahppen if we put holes in the sides of the container ?
WRITE YOUR OBSERVATINS .
-Water squirts out of the sides of the container :
-HWOEVER , water squirs out much further at the bottom hole than at the TOP hole .
-This is becuas ethe water of the bottom of the container is at a higher pressure than water at the top .
HOW DO WE CALCULATE PRESSURE ?
Pressure =height of column (m)Density of liquid (kg/mcubed)gravitiaitonal field strength (N/kg)
p=hpg P AT THE TOP FOR TRIANGLE .
-You will also be given other values , like density +gravitational field strength .
DO PRACTICE QUESTTION AT 120 .
Why do objects float or sink : (1)
-Shows an object , immersed in a liquid ,
-The pressure of a liquid depends on the depth .
-THE BOTTOM of the object is at a GREATER DEPTH , than the top of the object ,.
-Meaning that the BOTTOM of the object , experiences a LARGER PRESSURE than t the top .
Why do objects float or sink : (2)
-Because of this , there is a LARGER FORCE , acting at the BOTTOM of thre object than at the top of the obect .
-in aother word , there is a resultnt force acting UPWARDS , AKA AS UPTHURST .
Conditions for an object to float .
-For an obbejct to float , the upthrust must equal ,t he object;s weight (downward force due to gravity ).
-If the upthurst is less than the objects weight ,the object SINKS .
Object going to be lowered into water
-When we lower an object into water , the level of the water rises .
-*As the object DISPLCES the water .
-The size of the upthrust acting on the object , is the same ,a s the wiehgt of the water dispalced by the object .
-If an object can displace its own weight of water thn the upthurst will euqal the objects weight and the object will float .
