forces 2 Flashcards
what is work done
when force moves an object through a distance, energy is transferred and work is done
what is work done measured in
joules
what happens for an object to be in equilibrium
forces are balanced
to do you find the value if a missing for of an equilibrium
join given forces tip to toe then measure missing length
how do you resolve a force (horizontally and vertically) that is at an awkward angle
measure out the diagonal given then complete the triange in same scale
two types of elastic deformation with basic descriptions
elastic deformation:
can return to original shape/length
inelastic deformation:
doesnt return to original shape/length
relationship between extension and force
directly proportionate
HOWEVER at “limit of proportionality”, inproportionate
what happens to energy when something is elastically deformed
all energy transferred to objects elastic potential energy store
apparatus set up to measure link between forces and extension
weighted stand
clamp a spring from top
fixed vertical ruler to measure
hanging mass from bottom of spring
pilot experiment for extension practical
• find identical spring to spring used
• add masses one at a time
• measure extension each time
• if there is a bigger increase, limit of proportionality reached and smaller masses are needed
method for extension practical
• pilot method first
• measure unweighted length of spring at eye level
• add one mass, allow to rest
• record mass and measure
• record extension (change in length)
• repeat with 5 more masses
• plot force-extension graph
how to work out elastic potential energy (work done) of a spring calculated
E = 1/2 k e^2
epe = 1/2 x spring constant (n/m) x extension^2 (m)
how can you calculate elastic potential energy store of stretched sprng using graph
area under (linear) graph
equation linking weight, mass, gravitational field strength
weight (n) = mass (kg) x gfs (n/kg)
equation linking acceleration and change in velocity and time
acceleration (m/s^2) = civ (m/s) / time
equation linking final velocity, initial velocity, acceleration, distance
final v^2 - initial v^2 = 2 x acc x dist
how is terminal velocity reached in parachutist (sam)
• when sam first falls, gravity much higher than air resistance, accelerate
• as speed increases, so does air res
• eventually they balance, resultant force = 0
• terminal velocity reached
• parachute opens, area for air resistance increases but force pulling down stays the same
• terminal velocity decrease
what factors affect terminal velocity
area
shape
newtons first law
if resultant force on stationary object is zero it will remain stationary
if resultant force on moving object is zero it will remain moving
ms petosa
newtons first law
if resultant force on stationary object is zero it will remain stationary
if resultant force on moving object is zero it will remain moving
ms petosa
newtons second law
resultant force = mass x acceleration
newtons third law
when two objects interact, forces exerted on each other are equal and opposite
set for apparatus to investigate how mass and force affect acceleration practical
• trolley at starting line
• two light gate at stable distances on track, connected to data logger
• pulley attached to trolley
• masses hanging from trolley & pulley
what dies trolley/pulley practical investigate
how mass and force affect acceleration
what does spring/weights practical investigate
link between forces and extension
method for trolley/pulley practial
• connect trolley to string that goes over pulley and connects to masses
• mark starting line for accuracy
• let trolley go without masses to get original acceleration
• repeat, adding one mass, 5 times
• record data from light gates
f
equation linking stopping, thinking, and braking distances
stopping d = thinking d + braking d
three factors of thinking distance
alcohol
tiredness
distractions
4 factors of braking distance
speed
weather/road conditions
tyre conditions
brake conditions
equation linking momentum, mass, velocity
momentum (kg m/s) = mass x velocity
is momentum vector or scalar
vector
relationship between momentum before and momentum after
equal
what can conservation of momentum be used for
calculate velocities and masses
equation linking force, change in momentum and change in time
force (n) = change in m / change in t
why are cars designed to slow people down slowly when they crash
longer it takes for change of m -> smaller change of m -> smaller force -> less casualty
three safety car features
crumple zone
seat belt
air bag
