Mechenics Flashcards
what’s a scalar and vector
a scalar has no direction it’s just the amount of smth
ex. mass, temp, time, speed
a vector has magnitude and direction
ex. displacement, velocity, force, acceleration
what’s a moment and what’s formula
a turning effect of a force
M=Fd
force x perpendicular distance from the point to the line of action of force
what is equilibrium
the sun of the clockwise moments bout any point equals the sum of the anti-clockwise moments about the same point
what’s a couple
a pair of forces of equal size which act parallel to each other but in opposite directions
it doesn’t produce a turning effect
what does inertia mean
any mass has a resistance to a change in velocity when subjected to a force
what is centre of mass
it’s the single point that you can consider it’s whole weight to act through
how do you get the centre of mass of an irregular object
- hang the object freely from a point
- draw vertical line downwards from the point of suspension
- hang the object from a diff point
- draw anotherr vertical line downwards
- center of mass is where the two lines cross
how does an object topple over
if the vertical line drawn downwards from its centre of mass falls outside its base area
this happens because of a resultant moment occurs which causes a turning effect
the lower the centre of mass and the bigger the base area, the more stable the object is
what does acceleration mean
the rate of change of an objects velocity
whats velocity
the rate of change of an objects displacement
whats displacement
how far an object has travelled from its starting point in a given direction
what’s an ultrasound position detector and what are advantages of it
it’s a tote of data logger that automatically records the distance of an object from the sensor several times a second
this helps get real time displacement-time and velocity-time graphs
adv.
- data is more accurate (faster reaction times)
- have higher sampling rate than humans (take ten readings very second)
- you can see the data displayed in real time
what are the 4 SUVAT equations
- a=(v-u)/t
- S=ut+1/2at^2
- v^2=u^2+2as
- S=(u+v)/2xt
what’s the free falls experiment
- measure the night from the bottom of the ball bearing to the trapdoor
- flick the switch to simultaneously start the timer and disconnect the electromagnetic, releasing the ball bearing
- the ball bearing falls, knocking the trapdoor down and breaking the circuit which stops the timer. record t
- repeat this experiment three times and average the time taken to fall from this height. repeat this experiment but drop the ball from several different heights
- you can then use these results to find the g using a graph
what can help getting a smaller uncertainly when doing the free fall experiment
by using a computer automatically release and time the ball bearings fall
how to calc the gradient of the free fall experiment
g= 2xs/t^2
what is a systematic and random error of the free fall experiment
random — effected by wind to remove this error conduct the experiment indoors and close all windows
systematic — there might be a delay in the stopwatch/light gates to remove this ensure they are properly calibrated before conducting the experiment
whats newton’s first law of motion
velocity of an object will not change unless a resultant force acts on it
whats newtons 2nd law
the more force you have acting on a certain mass the more acceleration you get
F=ma
in what direction does the acceleration go
the same direction as the resultant force
why did galileo say
he said that all objects fail at the same rate
whats newton’s second law
if an object A exerts a force on object B then object B exerts an equal but opposite force on object A
two ppl are diving and they reach the water at the same time why? explain in newtons 2nd laws
the force acting on each diver is their weight =mg since F=ma this gives the equation
mg=ma which can be written as g=a so their acceleration doesn’t depend on their mass but rather there gravitational sooo they reach the same time
what are the two types of friction
dry friction (solid friction)
fluid friction (drag) ( fluid resistance or air resistance )
what are three things you need to know about frictional forces
- they always act opposite direction to the motion of the object
- they can never speed things up or start smth moving
- they convert kinetic energy into heat and sound
whats lift
lift is an upwards force on an object moving through fluid
it happens when the shape of an object causes the fluid flowing over it to change direction
it acts perpendicular to the direction fluid flows in
whats terminal speed
when the friction force equals the driving force
when frictional or drag force increase with speed
what are two ways of increasing a vehucles max speed
- increase the driving force — by increasing engine size
- reducing friction — making the body more streamlined
how is momentum always conserved
the total momentum of two objects before they collide equals to the total momentum after the collision
what is the difference between elastic and inelastic collisions
elastic collision is one where momentum AND kinetic energy is conserved meaning no sounds and no heat dissipated
inelastic collision is on where momentum is conserved but some kinetic energy is converted into other forms during collision
whats impulse and whats its formula
impulse is the change in momentum
Ft = mv - mu
(Ns )
what are three designs that help increase impact time for safety
crumple zones — parts of the front and back of the car crumple on impact to allow the car to have a longer stop increasing the impact time and decreasing force on passengers
seatbelts — these stretch slightly increasing time taken for the wearer to stop this reduces forces acting on chest
Air bags — these also slow down passengers more gradually and prevent from hitting hard surfaces like the dash board
helmet — has a special foam that is covered with air sockets allowing the helmet to take all the shock from the force instead of the head
what are 4 things of getting area under graph to calculate smth
calculating displacement
calculating work done
calculating impulse / momentum
elastic strain
what’s the principal of conservation of energy
energy cannot be created or destroyed. energy can be transferred from one form to another but total amount of energy in a closed system will not change
what are examples of scalar and vector
scalar
distance
speed
mass
energy
temp
vector
displacement
velocity
acceleration
force
momentum
