Understanding Pressure
3.1Understanding PressureChapter 3 Forces and PressureLearning
OutcomesWhat is Pressure?
Water pressure in fountain forces the water spray high in the
airHigh air pressure in a car tyre helps it to support a heavy
load.Pressure cookers are used for cooking food more quickly than
conventional cooking methods
Pressure
Pressure
Which shoe exerted more higher pressure to the ground?
Pressure
The base of high heeled shoe is small, as a result, the pressure
that acts on the ground is greaterThe base of flat shoe is large,
as a result, the pressure that acts on the ground is less.
PressureThe pressure on a surface also depends on the direction
the force is applied.If a force acts at a known angle to a surface,
only the component of the force which is perpendicular to the
surface is used to determine the pressure.
ExerciseFigure shows a cardboard box placed on a soft ground in
two different orientations.
Calculate the pressure exerted on the soft ground in each
case.
The pressure exerted by a given force increases as the surface
area decreases. It is to be noted that the pressure exerted on tip
of the drawing pin is 100 times greater than the pressure exerted
at the head of the drawing pin.This pressure drives the pin into
the wood.Applications of Pressure in Our Everyday LifeIn our daily
life, there are situations which require high pressure and low
pressure.
Reducing area to increase pressure
A sharp knife and a pair of scissors has a very small surface
area on its cutting edge.So that high pressure can be exerted to
cut object. Reducing area to increase pressure
The studs on a football boot have only a small area of contact
with the ground.The pressure under the studs is high enough for
them to sink into the ground, which help extra grip.Reducing area
to increase pressure
Ice-skate has a narrow metal blade fixed to its sole.The high
pressure exerted by the edge melts the ice allowing the skater to
glide smoothly across the surface of the ice.Reducing area to
increase pressure
Increasing area to reduce pressure
The Foundation of a building has a large horizontal base area in
contact with the ground.This reduces the pressure beneath so that
building does not sink into the ground.Increasing area to reduce
pressure
Skis have a large area to reduce the pressure on the snow, so
that they do not sink in too far.
Increasing area to reduce pressure
The large tyres of a tractor have large area of contact with the
ground.The reduced pressure prevents the tractor from sinking into
the groundIncreasing area to reduce pressure
Polar bear has wide paws.Large soles of snow shoes.Increasing
area to reduce pressure
A man placed some durians in a plastic bag and carried the bag.
After a while, the man noticed that the plastic bag is torn.
Why?
As a shop assistant, you are asked to place some nails bought by
a customer in a plastic bag. However, the plastic bag is very thin
and the nails will likely poke through it. Suggest a way to place
the nails in the plastic bag so that the plastic bag will not be
poked or torn by the bails.Explain your answer
Figure (a) shows a boy sitting on a horizontal wooden bar.When
he stand s on the same horizontal bar as shown in figure(b) it
breaks.(i) States one physics quantity that. Remains constant in
both figure (a) and figure (b). Varies from figure (a) and (b)(ii)
Explain why the bar does not break in (a) but breaks in (b)
Diagram shows a wooden block acted upon by a force.What quantity
increases when a greater applied force is used?
