FORCES #2 Flashcards
what is newtons first law
if the resultant force on astationary object is zero the object will remain stationary. if the resultant force on a moving object is zero itll carry on moving at the same velocity
the larger the resultant force on a object…
the more the object accelerates
force and acceleration are …..
directly proportional
equation for newtons second law
f=ma
what is inertia
inertia is the tendency for motion to remain unchanged
what is newtons third law
when two objects interact the forces they exert on each other are equal and opposite
how do you find inertia mass
m=f/a
example of newtons third law
is a man pushing against a wall
as he pushes against the wall there is a normal contact force acting back on him
the two forces are the same size
as the man applies a force and pushes the wall the wall pushes back on him with equal force
stopping distance =
thinking distance + braking distance
what is thinking distance
is how far the car travels during the drivers reaction time
what is braking distance
is the distance taken to stop under the braking force
what is thinking distance affected by
your speed, the fast you’re going the further youll travel
reaction time,
the longer your reaction time the longer your thinking distance
what is braking distance affected by
your speed
theweather
condition of your tyres
the larger the braking force
the larger the deceleration
what can reaction time be affected by
tiredness
drugs
alcohol
how can you measure reaction time
ruler drop test
as a car speeds up….
thinking distance increases at the same rate
braking distance increseases ….
faster the more you speed up
momentum=
mass * velocity
the greater the mass of an object or the greater its velocity….
the more momentum it has
momentum before =
momentum after
what is the conservation of momentum
in a closed systek the total momentum before an event is the same as after the event
describe how momentum has been conserved by a gun recoiling
before the gun fires a bullet the toral momentum is zero
when the bullet leaves the gun it has momentum in one direction
the gun moves backwards so it has momentum int he opposite direction
this measn that the total momentum after the bullet has fired is zero this means momentum has been conserved
force = (momentum)
change in momentum/change in time
a larger force means…..
faster change in momentum
car safwty featues
crumple zoens crumple on impact increasing the time taken for the car to stop
seatbelts slightly increasing the time taken for the weare to stop
air bags inflate before you hit the dashboard of a car
how are bike helmets designed to reduce the impact of a fall (talk about momentum and time)
contain a crushable layer of foam which helps to lengthen the time taken for your head to stop in a crash
which means there is a longer change in momentum
how are crash mats designed to reduce the impact of a fall (talk about momentum and time)
they increase the time taken for you to stop if you fall on them which means there is a longer change in momentum
why are cars designed to slow people down over a longer time when peole crash
the longer the takes for a change in momentum the smaller the rate of change of momentum so the smaller the force
less force means less servere injury
the longer the time taken for a change in momentum
the smaller the force
a larger force or a larger distance means..
a larger moment
what does it mean when an object has been elastically deformed
can go back to original shape or length
what does it mean when an object has been in elastically deformed
doesn’t return to original shape or length
why do we need to push at right angles
because pushing at any other angle means a smaller distance, and so that means a smaller moment
a force transmitted to a larger gear…
will cause a bigger moment, as the distance to the pivot is greater
the pressure of a fluid means…
A FORCE IS EXERTED AT RIGHT ANGLES TO ANY SURFACE IN CONTACT WITH A FLUID
what do objects in fluids experience
upthrust
pressure increases with…
depth
an object floats if its weight =
upthrust
how do submarines use upthrust
to sink, large tanks are filled with water to increase the weight of the submarine so that it is more than the upthrust
to go to the surface the tanks are filled with water to increase the weight of the submarine so that it will be more than the upthrust
atmospheric pressure decreases with…
height
how Is atmospheric pressure created
on a surface by air molecules colliding with the surface
what is velocity
speed in a given direction
why when the altitude increases does the atmospheric pressure decrease
because as the altitude increases the atmosphere gets less dense so there are fewer air molecules that are able to collide with the surface
measuring displacement
displacement measures the distance and direction in a straight line from an objects starting and finishing point
example of measuring displacement
if you walk 5m north then 5m south the displacement is 0m as its in a straight line
the total distance is 10m
Mark walks her dog after skl she takes a route of 1500m that starts and returns to her home
what is the distance she travels
whats her displacement
distance= 1500m displacement = 0m
typical every day speeds walking running cycling car train plane
walking- 1.5m/s running- 3m/s cycling- 6m/s car- 25m/s train- 55m/s plane- 250m/s
what is the number for acceleration due to gravity(falling object)
9.8m/s2
when calculating uniform acceleration of a ball dropping what do you use for the acceleration
9.8m/s2
how do you find the acceleration at a point on a velocity time graph
use a tangent to the curve at a point
what is drag
resistance you get in a fluid, gas. or liquid
how do you reduce drag
make the object stream lined
example of drag
air resistance
