mechanics Flashcards
when a object is in equilibrium, what are the forces doing?
all forces acting on it are balanced and cancel each other out. there is no resultant force acting on the object
how do you find a missing magnitude of a force when a particle is in equilibrium and three forces are acting (one vertical another horizontal, one diagonal)?
draw the forces tip to tail, then use Pythagorus to work out the missing length.
how to resolve three forces at different angles for a body in equilibrium
sum of the vertical components = 0
sum of the horizontal components=0
work these out using trigonometry
what’s a good way of investigating equilibrium?
force boards- you can apply forces to an object in different directions and when at equilibrium, the object will be in the middle.
what are the two main types of friction?
contact- between solid surfaces
fluid-liquid or gas
what are the three factors that effect fluid friction?
the thickness (viscosity) of the fluid
force increases as speed increases
the larger the area pushing against the fluid, the greater the resistive force
what do frictional forces convert kinetic energy into?
heat
what is lift force?
an upward force on an object moving through a fluid
when does a lift force occur?
when the shape of an object causes the fluid flowing over it to change direction
when does terminal speed occur?
when frictional forces equal the driving force
an object will reach it at some point if there’s a driving force that is constant and a resistive force that increases with speed
what will happen to the forces if a car speeds up with a constant driving force?
the air resistance on it will increase as speed increases until its equal to the driving force, it will then be travelling at maximum speed and terminal velocity
what are the two main ways of increasing a car’s maximum speed?
increase driving force eg. increase engine size
reduce frictional force eg. more streamlined
how could you investigate terminal speed in a fluid?
put elastic bands around the tube of viscous liquid at fixed distances using a ruler
drop a ball bearing into the tube
use a stopwatch to record the time it reaches each band
repeat this, use a strong magnet to remove the ball bearing from the tube
calculate and average time and use this and distance to work out average velocity
as soon as a skydiver leave the plane what happens and when do they reach terminal velocity?
they accelerate downwards until air resistance equals their weight
they will then travel at terminal velocity
this velocity is too large to land safely so just before hitting the ground open parachute
this immediately increases air resistance so its bigger then weight
this slows them down until weight equals air resistance again
then reaches a lower terminal velocity which is small enough to survive the landing
what’s newton’s first law of motion?
the velocity of an object will not change unless a resultant force acts against it
what’s newton’s second law?
the acceleration of an object is proportional to the resultant force acting on it
F=ma
what’s newton’s third law?
if object A exerts a force on object B, then object B will exert and equal and opposite force on object A
how can you find change in velocity from an acceleration time graph?
area under the graph
how do you find acceleration from a velocity time graph?
the gradient
how do you find displacement from a velocity time graph?
area under the line
whats an ultrasound position detector?
a type of data-logger that automatically records the distance from the sensor multiple times every second
what are some advantages of using data loggers over traditional methods for drawing graphs?
more accurate data, eliminates human reaction time
much higher sampling rate then humans
you can see the data displayed in real time
if an object is accelerating, what will the displacement-time graph look like?
curved line with an increasing gradient
when is linear momentum conserved?
assuming there is no external forces, always
