Please enable JavaScript.
Coggle requires JavaScript to display documents.
Unit 9 Forces and motion (9.1 seeing forces (a force can act "on an…
Unit 9 Forces and motion
9.1 seeing forces
a force can act "on an object" by
PULL
something open
STRETCH
a rubber band
PUSH
a car
TURN
a door handle
eg: engine PULLS with big force to make the load of car move forward
Force cannot be seen - only felt
we feel using nerve endings to detect pressure
when sit on hand on chair
hand squashed by 2 forces
force of body pushing DOWN
force of chair pushing upwards
use force arrows to show
DIRECTION
in which force is acting
shows 2 things
the object that the force is acting on
the object that is producing the force
forces appear when 2 objects interact with each other
9.6 patterns of falling
objects
SPEED UP
when falling when there is
no AIR RESISTANCE
on it
galileo leaning tower experiment - dropped small iron and big iron ball ==> BOTH LANDED AT SAME TIME. because air resistance on iron balls are small and so different weight still falls at the same
RATE
of acceleration
9.3 weight - pull of gravity
earth's gravity pull objects downwards
TOWARDS CENTRE OF EARTH
the force is called weight and measured in Newtons
weight = force of gravity on an object
mass measured in kg
amount of matter in an object
dont fall through the floor because floor pushes UP with
contact force
contact force balances the pull of gravity
if you stand on something not strong, contact force may not be equal, and you fall through
9.4 friction - an important force
there is a heating effect of friction
friction = a force that can appear when 2 objects are in contact with each other
friction acts in the OPPOSITE direction to the pushing force ==> FRICTION ACTS TO OPPOSE MOTION (note for force arrows - shld be in opp direction
when pushing force >> than Friction then object moves
remove friction to reduce the force needed to push something
lubrication/ rolling rather than sliding, reduce weight, reduce contact area/ smoothen surfaces etc
9.2 Forces big and small
forces cause things to happen
"
PULLING
" forces measured by using a
FORCEMETER
/
NEWTONMETER
eg: measure the force needed to pull a block of wood
how to use forcemeter - instructions p. 131
spring inside the forcemeter is stretched when there is a force
the >> the force ==> the greater the number on scale
force measured in NEWTONS (N)
PUSHING forces measured using a weighing scale
the pressing of the scales causes dial to increase
reading in kg
needed to be convert to newtons
==> X10 ; 1kg = 10 N
earth's gravity pulls on each kg with a force of 10N
50 kg = 500N
examples
stand on scale - measure downward force of weight
push against wall with hands or feet measures pushing force
9.5 air resistance - force on objects moving through air
falling through the air is not really fast because there is AIR RESISTANCE acting on it to slow it down.
eg: parachustists ==> weight acting down and air resistance acting upwards
parachute must have big surface area to increase air resistance and slow down object eg: thistle seed
an airplane has to be
streamlined**
to reduce air resistance** so that it can move through air quickly
this EQUAL and OPPOSITE force slows down parachute to safe speed
I.E A BALANCED FORCE - the forces cancel each other out
flying squirrel also uses air resistance to glide through air
FRICTION AND AIR RESISTANCE SLOWS DOWN MOVING OBJECTS
compare