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forces and pressure forces (isabelle) - Coggle Diagram
forces and pressure forces (isabelle)
force
push or pull
push - typing on computer
pull - opening a cupboard
facts
SI unit - Newton (N)
effects of force
change direction of moving object
change speed of moving object
change size of object
stop moving object
change shape of object
make stationary object move
contact
force results when two interacting objects are in direct contact
frictional force
occurs when two objects are in physical contact
acts in opposite direction + opposes motion of object
greater when object moves on rough surface than on smooth surface.
ADVANTAGE OF FRICTION IN OUR DAILY LIVES
daily activities
sole of shoes, surface of roads allow walk, stand/run w/o slipping/sliding.
holding onto objects
enables iron nails to hold objects together.
slowing down/stopping objects
between brakes, wheels allows vehicle slow down/stop
door stopper prevent doors from closing.
moving across rough surface
between wheels, soil allows vehicle move across muddy field.
writing
pencil make mark on papers, eraser remove mistake.
slows down/stops moving object
WAYS TO OVERCOME FRICTION IN OUR DAILY LIVES
using ball bearing, rollers/wheels
allow wheels turn on axle easily + reduces wastage of energy
conveyor belts rotating metal rollers > transport heavy objects easily.
heavy objects e.g. refrigerators, shelves/machines > can be moved easily.
using cushion of air
reduces direct contact + reduce friction.
method used in transportation e.g. hovercraft/Maglev train.
makes objects ‘float’ on water/track > can travel at high speeds.
using lubricating oil/grease
surface smoother, object less friction + does not wear out quickly.
DISADVANTAGE OF FRICTION IN OUR DAILY LIVES
wear and tear
causes shoes, tyres, moving parts in machine, use - moving until worn out.
wastage of energy
produces heat > wastage of energy.
more energy needed move object > friction opposes motion.
non-contact
force applied to object by other object (no direct contact)
gravitational force
facts
force that pulls. acts between two masses w/o direct contact (gravitational force)
every object on Earth has mass and weight.
magnitude of gravitational force affected by two factors.
mass of object
object larger mass greater ~. e.g. Earth's ~ greater than Moon > mass Earth greater.
distance between two masses
distance between two masses increases, ~ decreases.
gravitational field region, object experiences ~ from other object.
~ of Earth pulls all objects towards its centre.
object placed within gravitational field of Earth, fall toward surface.
weight
~ causes objects have weight - is measure of amount ~ acts on it.
more mass , stronger ~ acting on it. more this object weighs.
gravitational field strength (g) amount of ~ acting on a 1 kg mass. Earth exerts ~ of 10 N on every 1 kg of an object.
Weight (N) = Mass (kg) × Gravitational field strength (N/kg)
magnetic force
force of attraction between magnets + magnetic substances.
X all metals magnetic substances.
iron, nickel, cobalt common magnetic substances. steel, alloy made mainly of iron also
magnet can exert force of attraction (pull)/repulsion (push) on another magnet.
useful - magnetic needle in compass shows direction > navigate jungles + oceans.
difference between mass + weight
SI unit
kilogram (kg)
newton (N)
measuring tool
Beam balance/electronic balance
spring balance
definition
mass - amount of matter in an object
weight - size of gravitational force acting on object.
consistency
mass remains unchanged in different locations
weight of object varies in different locations.
pressure
is defined as the force acting per unit area.
(N/m2 or Pa) force(N)/area(m2)
SI unit - newton per square metre (N/m²) / pascal (Pa).
measure of how applied force, distributed over particular area
force increase, area unchanged/decrease = pressure increase
useful - sharp knife cut objects more easily than blunt one because thinner blade concentrates force over smaller area, hence a ^ pressure can be produced.
liquids + gases also exert pressure because they have weight
as depth of water ^, pressure exerted on object also ^.
calculation
example 1
force of 50N applied over 0.4 m².
whats the pressure acting on this area?
Force = 50 N Area = 0.4 m² Pressure = 50N/0.4 m² = 125 N/m²
example 2
.
when object of 20 kg placed on floor, exerts a pressure of 80 N/m²
what is the area of the floor?
weight = gravitational field strength
= 20 kg × 10 N/kg = 200N
weight is the force exerted by the earth on the object
area \= 200 N ÷ 80 N/m² \= 2.5 m²
(Take g as 10 N/kg)
example 3
when a force is applied over an area of 8.0m², the pressure is 15.0kN/m².
what is the force applied on
Area = 8.0 m²
Pressure = 15.0 kN/m²
force = 8.0m² x 15.0 kN/m² = 120.0 kN
weight and mass
example 1
if object has mass of 55kg, what is its weight? take g as 10N/kg
weight = mass x gravitational field strength = 55kg x 10 N/kg = 550N
example 2
weight of metal rod is 25.4 N. what is total amount of matter in it? take g as 10 N/kg
mass = weight/gravitational field strength = 25.4 N/10 N/kg = 2.54 kg