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Chapter 9 Applications and Transfer of Forces, image, weight…
Chapter 9
Applications and Transfer of Forces
how do forces in nature affect us?
natural disasters
tsunami
weathering
volcanic eruption
earthquake
typhoons
landslides
forces
a force is a
push
or
pull
a force can be
contact
or
non-contact
⤷
contact force:
the body
exerting
the
force must
be in
physical
contact with the
object
examples are frictional force, applied force and elastic force
⤷
non-contact force:
the body
exerting the force
is
not
in
physical
contact with the
object
examples are gravitational force (weight), magnetic force and electrostatic force
a
spring balance
is used to
measure force
⤷ there are
two
types of spring balances:
extension
spring balance and
compression
spring balance
mass
amount of matter in a body
S.I. unit: kilogram (kg)
measured using
beam
balance or
electronic
balance
remains the same
no matter the change in
gravity
what happens when two or more object interact?
forces can change the
rest
or
motion
of objects
forces can..
move
a
stationary
object
change the
speed, direction or stop
a
moving
object
turning effects of forces
moment
is defined as the turning effect of forces.
S.I. unit: newton-metre (Nm)
pressure
⤷ is defined as the
amount of force
acting
perpendicularly
(90 degree angle)
on a
unit area
S.I. unit:
newton per square metre
(N/m²)
or pascal
(pa)
calculate
pressure using:
or..
where
F (force) = N, A (area) = m²
:star: when force increases, pressure increases
when area increases, pressure decreases
force always acts from
higher
pressure to
lower
pressure
applications of pressure
advantages
cutting edges
of knives :arrow_right:
easier
to cut
spikes
on the soles of football shoes :arrow_right:
increases grip
disadvantages
heels
leaving
marks
on wooden flooring
car tyre
gets
punctured
after rolling over
sharp objects
pressure in liquids
↳ pressure increases as depth of liquid increases
in submarines, the rigid metal bodies can withstand high amounts of pressure underwater.
atmospheric pressure
↳ is the pressure exerted by the air in the earth’s atmosphere
drinking through a straw
suction cup
work done
⤷ is the transfer of energy by the application of a force
S.I. unit: Joules (J)
there is work done only when
a
force
is
applied
, and
the force causes the
object
to move in the
same direction
there
is work done
in this image as the man is applying force
and
the box is moving in the direction of the force.
possible exam questions!
finding the area of contact
qn: a box of weight
200 N
is placed on the table. it exerts a pressure of
250 Pa.
calculate the area of contact between the box and the table.
first, rearrange the formula to make the area the subject
p = f/a
area = N/Pa
next, substitute the values into the formula
area = 200N/250Pa
calculate the equation
200N ÷ 250Pa = 0.8m² (answer)
finding weight
qn: calculate the weight of a
250 g
apple on Earth, given that the gravitational field strength,
g = 10 N/kg.
first, convert 250g into kg.
1kg = 1000g
250g = 250/1000 = 0.25kg
next, substitute the numbers into the formula.
weight = mass (kg) x N/kg
0.25 kg x 10N/kg = 2.5 N (answer)
finding pressure
qn: a box of weight
3.0 N
is placed on the floor. the contact area between the box and the floor is
0.45 m²
. calculate the pressure exerted on the floor by the box.
first, substitute the numbers into the formula.
Pa = 3.0N/0.45m²
calculate the equation
3.0N ÷ 0.45m² = 6.6666...
≈ 6.67Pa (3 s.f.) ans
if they give the area in cm², convert it to m² using this formula:
1m² = 10,000cm²
energy conservation
:star: Energy
cannot
be
created
or
destroyed
, but can be
converted
from one form to another. The
total energy
in an isolated system
remains constant.
⤷ S.I. unit: Joules (J)
weight
gravitational force acting on the body
S.I. unit: newton (N)
measured using
spring balance
changes
according to
gravity
calculate weight: weight (N) = mass (kg) x gravitational field strength (N/kg)
vs
electronic balance
beam balance
spring balance
however, there is
no work done
in this image. although the man is applying force onto the briefcase, the briefcase
did not
move in the direction of the force.
100J
