force and pressure

Question 1

what is pressure?

Answer 1

• caused when objects exert forces on each other
• or when a fluid exerts a force on an object in contact with it
• depends on the area of contact on which the force acts and the size of the force

Question 2

what is the definition of pressure

Answer 2

the force per unit area

Question 3

what is the equation for pressure?

Answer 3

pressure(Pascals,Pa)=force(N)/area(m2)

Question 4

what is the equation for weight?

Answer 4

W=mg

Question 5

How do you get from cm2 to m2?

Answer 5

divide by 10,000

Question 6

How would you measure the pressure of your foot?

Answer 6

• draw around your foot on centimetres squared paper
• count the number of centimetres squared in each footprint to find the area of contact in square centimetres
• convert to square metres
• use a scale to measure weight in newtons, or kg and use weight equation, to find force
• work out pressure using weight/area

Question 7

why do sharp knifes cut easier than blunt knifes?

Answer 7

• smaller area of contact so pressure is greater (proved by equation)
• so bigger cutting affect when same force is applied

Question 8

how would you conduct an experiment to measure the pressure inside an inflatable bag?

Answer 8

• with a bag deflated, place a weight on a card on the bag.
• use the hand pump to inflate the bag until the card and the weight is raised.
• The pressure in the bag is equal to the pressure of the weight on the card
• measure the area of the card, then use the equation to calculate pressure

Question 9

what is a fluid?

Answer 9

• something that can flow and fit into its container
• liquid or gas

Question 10

why would a diver not be able to breathe through a long snorkel

Answer 10

at a depth, the divers chest muscles would not be strong enough to expand her chest muscles against the water pressure on her body

Question 11

what is the equation and rule for pressure in a liquid?

Answer 11

• pressure in a liquid increases with depth
• a liquid flows until the pressure along the same horizontal level is constant
• pressure of a liquid=height of column(m)density of liquid(kg/m3)gravitational field strength(N/kg)

Question 12

what is the value of atmospheric pressure at sea level

Answer 12

100,000kPa
so the force on each square metre of surface at sea level is about 100,000N

Question 13

What effect would the pressure in the sea have on your body

Answer 13

• increase in pressure causes more gases to dissolve in the blood stream
• if time isnt allowed for your body to adjust, it can’t adjust to the new external pressure
• decompression sickness disease-when dissolved gases (N2) comes out of solution in bubbles and can affect any body area
• can be fatal unless time is allowed for body to adjust in a decompression chamber

Question 14

the greater the density of a liquid

Answer 14

the greater the pressure of a liquid

Question 15

Do mass, surface area and the geometry of the container affect pressure?

Answer 15

no, it does not matter if depth and height are the same

Question 16

what causes an object to float?

Answer 16

if upthrust and weight are the same

Question 17

what is upthrust?

Answer 17

when a partially or totally submerged object experiences a greater pressure on the bottom surface than on the top, creating a resultant force upwards

Question 18

whatt is the atmosphere

Answer 18

a thin layer of air around earth that gets less dense with increasing altitude
extends more than 100km into space

Question 19

what causes atmospheric pressure?

Answer 19

• air molecules colliding with a surface
• the number of air molecules (so weight of the air) above a surface decreases as the height of the surface above ground level increases
• so as height increases, there is always less air above a surface than at lower height
• so air pressure decreases with an increase in height

Question 20

what is kinetic theory

Answer 20

• air pressure is caused by air molecules colliding with a surface
• air molecules each exert a tiny force
• motion is random

Question 21

what is the equation for pressure at sea level?

Answer 21

pressure (Pa)=height(m) * density(kg/m3) * gravity(N/kg)

Question 22

how would you conduct an experiment to investigate upthrust

Answer 22

• use a newton metre to weigh a metal object in air
• repeat by weighing the same object when completely in water
• results: newton metre reading is less when in water because it experiences an upthrust
• the difference between the 2 newton metre readings is the upthrust acting on the object
• if partially submerged, will be between the 2 values

Question 23

why does a can collapse when heated?

Answer 23

• when you heat a bottle or can, air particles gain kinetic energy
• causing them to pass out the end of the can, meaning there is less pressure on the inside
• if you put the lid on and cool it again, the air pressure pushing in is greater than the inward pressure pushing out
• so can collapses

Question 24

how can suction caps stick to the wall?

Answer 24

• when pressed on the wall, air is sucked out
• this means that inward pressure is greater than outward pressure
• producing an inward force (atmospheric pressure is greater)

Question 25

why do objects that are more dense than the liquid sink?

Answer 25

- its weight is greater than the weight of the liquid displaced, so greater than the upthrust

Question 26

What is the atmosphere and how does it change with height?

Answer 26

- a thin layer of air around the earth - extends 100km into space - the density of the atmosphere decreases with altitude, there are fewer molecules per cubic metre - so atmospheric pressure decreases with altitude - p=hpg for density

Question 27

How does atmospheric pressure act when you drink through a straw?

Answer 27

- air is sucked out of the straw so the atmospheric pressure acting on the surface outside the straw pushes the liquid up