Forces Flashcards
what are scalar quantities
have magnitude ( size) only
example of scalar quantities
mass, speed, energy, distance, time, tempt
what is vector quantities
have magnitude and direction
exmaples of vector quantities
displacement, weight, velocity, force, acceleration, momenutum
how to represent vector quantiity by arrow
- length of arrow - magnitude
- direction of arrow - direcetion
what is a force
push or pull that acts on an object due to the interaction with another object
what are 2 types of forces and meaning
contact force = objects are physically touching
non-contact force= objects are physically seperated
examples of contact force
tension - in a rope of tug of war game, tension on rope pulling the person
friction - force always opposes the motion, areoplane land in sea, frcition act betwen plane and water to cause the plan slow down and stop.
air resistance - force act opposite direction when object move through air - sky diver from air, air particles collide with parachute causing act upwards cos of air reistance force.
-upthrust
exmaples of non-contact force
-gravitational force - attracts all objects to another object - grav force attract international space station to earth and opposite way
- electrostatic force - force between 2 charged object attract, object opposite charge experience electrostatic force of attraction.
-magnetic force - force experince by certain object in magentic field
what is weight and unit
the force acting on object due to gravity, newton W
what to use for measuring weight
newtonmeter
what is gravity
force of attraction on all objects
what is gravitational fiedl strength
measure of the force of gravity
weight of object is…
directly proportional to mass of object
what does weight of object depend on
the gravitional field strgth at point where object is
what is centre of mass
weight of object act on single point
what is resultant force
single force that has same effect as all forces acting together
how to calculate resultant forces
larger force-smaller
convert newton-metres to joule
1newton metres=1 joule
when is work done on object by force
when a force causes object to move through a distance
what is elastically deformed
object can return orginial shape when force cause it to change shape are removed
why do you need to apply more than 1 force in elastically deformed
the force is unbalance so the object will move than change length/shape
elastic materials examples
slinky, rubber band and glove, eraser
what happens when squeeze force
material compresses
what is inelastically deformed + why
object cant return orginally, because limit of proportionally been exceeded
what does limit of proportionally mean
point where extension of object is direct proportional to force.
what is the moment of force
the turning effect of a force
examples of turning effect of force
see-saw, a crane, hammer use to remove a nail
example of turning effect force in rotation
spanner use to loosen a nut(screw), the turn effect of force from end of spanner is centre around the pivot(centre of nut)
what is a pivot
centre of object
how should you calculate the moment
distance must be in perpendicular from line of action to pivot (90 degree)
exmaple of balance moment of pivot
see-saw person both ends, seesaw balance about the pivot in cnetre. each person apply moment due to weight.
what is lever
rigid bar set on pivot, sued to transfer force to load. force multipers
exmaple of lever use
hammer use to removve nail, crowbar use to lift a plank of wood
what is gear
transmit tun effect of force, lots of machine and cars
what can lever and gear system do
can both be used to transmit the rotatioanl effect of force
what is fluid
either liquid or gas
what happens when particles move around in fluid
collide object surface/container
what is atmosphere
thin layer of air around the earth
when does atmospher get dense
less dense with increase altiude
what is altitude
vertical height of object
how to create atmospheric pressure
air molecules colliding with surface
what happens when number of air molecules above a surface
decreases as height of surface above ground level increase
what is distance
how far an object moves
what is displacement
the measure of distance that object moves in straight line from start point to end, and direction of straight line
what does the speed which person can walk, run etc depend on
age, fitness, distance travel, terrain
speed of
walk, run, cycle, car, train, areoplane, sound air
1.5m/s, 3, 6, 13, 50, 250,330
what is acceleration
of an object tells us the change in its velocity over a given time
what does the gradient tells us about acceleration
horizontal line - constant
upward slope- accelertaing
downward slope- decelerating
what is a velocity
speed of an object in directio
what is newton 1t law
resultant force acting on object is zero then,
object stationary = remain staitionary (not moving over time)
object moving= continue to move at same speed and direction, same velocity
in newton1st law, when do velocity change
velocity of object only change i resulatn force acting on object
exmaple of newton law 1
statinoary object(book on table, person standing), no force acts on bceause no resulatnt force. Object 50N left and right, fore is balance means resualtn forceis zero, and velocity same.
what is newton 2nd law and sign
acceleration of object is proportional to the resultant force acting on object and inversely proportional to mass of object
what happens to resultant force act on object onnewton 22ndlaw
if greater force = greater acceleration
what happens to inversely proportional to mass of object newton2newton2law
is mass large = accerlation smaller
what is newton 3rd law
whenever 2object interact, the force they exert on each other are equal and opposite.
what is equilibrum
and equilibrum situation
condition system of state motion, speed, time change
all force act on object is balanced.
example of newton 3rd law
book kept on table, man in canoe, paddle push on water same time the water push back on paddle = equal magnitude and oppoisye direcetion
what is thinking distance
distanc vehicle travels during the driver’s reaction time
what is braking distance
distance travels under braking force
what reaction time
time tkaen for driver to spot obstruction and make decison
how to calculate stop dist
think dist + brake = stop
what affects drivers reaction time
-tiredness
-drugs alchol
-distraction phone
typical value of reaction time
0.2-0.9m/s
what can affect brake distance of vehicle and why
weather conditions - wet/icy road
poor condition of vehicle - worns tyres+brakes
these reduce friction of tyre and road, and increase brake dist
the greater the speed of a vehcile…
the greater braking force
the greater braking force…
greater the deceleration of vehicle
what can large deceleration lead to
brakes overheat and loss of control
what is conservation of momentum
in closed system, total momentum before an event is equal to the total momentum after the event.
when does change in momentum occur
when force act on object that is moving/able to move
why is rapid changes of momentum danger
lead huge forces away
how to reduce momentum danger
airbag, seatbelt, crashmat, bike helmet - safety device to slow down and reduce force act
terminal velocity steps and after parachute opens
- when jump out of plane, force of gravity on weight pull them down toward earth.
- resultant force same size and direction cos only weight force happened
- Person start to fall, air resistance occurs in upward force, it will be opposite direction of weight and resultant force. Air resistance comes cos person collides between air particles causing the person to slow down.
- so resultant forc3e low and aie resistance
- Faster goes the velocity increase and air resistance cos collide with particles more. Resultant force decreases
- Velocity soon get high and particles collide increase will then air resistance and weight same size so 0 resultant force reaching terminal velcoity.
- OPEN PARACHUTE , surface area of parachute increase so does air resistance, so resultant force act upward and decelerate downwards - causes to slwo down
- further slows down, air resistance lower and resultant force smaller . The air resistance and weight same size and equals. this is resultant force 0 and reaches terminal velocity.
Gears example with gears in car - turn effect
Gear A - connect engine
Gear B - connect wheels.
The gear B transmite 2x larger Gear A and turning effect will be 2x bigger.
So engine turn effect has been doubled pass to the wheels
spring constant high=
spring constant low=
stiffer, harder to stretch
less stiffer and firm , easier to strech
