Mechanics Flashcards
define distance
scalar or vector, why
a measure of the total length moved by an object
scalar because it doesnt take direction into account
define displacement
scalar or vector, why
how far an object is from its starting position
vector because it takes direction into account (it can be north east south west)
define speed
scalar or vector, why
a measure of how the distance changes with time
scalar since neither distance or time are vectors so direction is not taken into account
define velocity
scalar or vector, why
the rate of change of displacement
vector because displacement is a vector so direction needs to be considered
define acceleration
what is the equation and units
scalar or vector, why
the rate of change of velocity
change in velocity / change in time = acceleration
ms^-2
vector because velocity is a vector so direction needs to be considered
what is uniform acceleration
constant acceleration
the acceleration changes by the same amount each unit of time
what does the gradient signify on a displacement time graph
the velocity
what does the gradient signify on a distance time graph
the speed
how can you calculate the gradient
change in y / change in x
what does a horizontal straight line on a disp-time graph indicate
stationary
what does a positive diagonal straight line on a disp-time graph indicate
a constant velocity in an object whose displacement is increasing
what does a negative diagonal straight line on a disp-time graph indicate
a constant velocity in an object whose displacement is decreasing
what does a curved line on a disp-time graph indicate
the object is accelerating
what is stopping distance
how can you calculate it
the minimus disance that a car can safely stop in
the thinking distance plus the braking distance
what factors may affect thinking distance
alcohol
drugs and medicines
tiredness
distractions
speed
define thinking distance
the distance traveled by the vehicle in the time it takes for the driver to react and step on the brakes
what factors may affect breaking distance
speed
weather
condition of tires and brakes
condition of road
generally anbything that affects the friction between the road and the tired
define stopping distance
the distance traveled by the vehicle while the braking force acts
in what situation can we use suvat
when an object uniformly accelerates
what does each letter of suvat stand for and their units
s - displacememt m
u- initial velocity m/s
v- final velocity m/s
a- acceleration m/s^2
t- time s
what are the four suvat equations
v = u + at
s = 1/2 (u + v) t
s = ut + 1/2 at^2
v^2 = u^2 + 2at
what is acceleration due to gravity
9.81m/s^2
what is a projectile
an object on which the only force acting is weight
at a projectiles maximum height what is its velocity
0m/s
how can we use suvat to find parameters of a projectiles motion
when the projectile is thrown at an angle, you can separate the initial velocity into the horizontal and vertical components the same way as you do with forces
uou can then use suvat tk find different parameters kf the projectiles motion
describe the horizontal velocity in parabolic motion
the horizontal component will always have an acceleration of 0 and the velocity will be constant throughout the whole journey
describe the vertical velocity in parabolic motion
the vertical velocity will be always affected by the objects weight, hence the acceleration on earth will always be 9.81m/s^2.
the object, if thrown upwards, will decelerate downwards due to gravity before reaching its peak displacement at a velocity of 0, then accelerating down due to gravity.
describe how we can determine g in a practical
g can be determined by dropping a ball from different heights and measuring the time or velocity with which it falls
this can be done using a lightgate or a stopwatch
what is newtons first law
an object will remain at rest or at constant velocity unless it is acted on by an external resultant force
what is newtons second law
the rate of change of an objects linear momentum is directly proportional to the resultant force
the change in momentum takes place in the direction of the force
what is newtons third law
for every force between two surfaces each surface will exert an equal and opposite force of the same type towards eachother
how can you calculate weight
mass in kg times by 9.81
define what the centre of mass is
the point on an object where the mass can be thought to act through
how can we find the centre of weight of an irregular object
the object is hung from a pin or from a clamp stand so that it is freely suspended from one point
a string taut with mass (plumbline) is hung in front of the object in line with the point from which it is suspended and a line is drawn where the string is
repeat this process for other points on the object
the centre of mass will be where all the lines meet
describe the forces acting on a car moving at a constant velocity
north - normal force
east - driving force
south - weight
west - friction and air resistance
the N and S forces will be equal
the E and W forces will be equal
the resultant force will be 0
what is the acceleration due to gravity
9.81m/s^2
what is terminal velocity
the maximum velocity reached by an object moving through a fluid
what does acceleration in free fall depend on
the gravitational field strength of the planet
why does an object reach terminal velocity
as it falls, the drag forces get bigger and bigger and eventually equal the weight so that the resultant force is 0 and the object falls at a constant velocity
describe the motion of a skydiver, explaining each part in terms of forces an acceleration
as soon as he jumps, the resultant force and acceleration are the greatest because the drag is almost 0
as he falls and his velocity increases, his drag increases and the resultant force decreases so his acceleration decreases
eventually, the drag will equal his weight an he will fall with an acceleration of 0 because the resultant force is 0
why does someone who falls with a parachute have a lower terminal velocity compared to someone without one
a parachute will increase the rate with which drag increases on a falling object, leading to the object accelerating for a shorter time, and the velocity being able to increase for less time, hence leading to it being smaller
what is a moment
the turning effect of a force around a fixed point a pivot
what are the three parts of a lever
the load
the effort
the pivot
what is the equation for a moment
moment = force * perpendicular distance from force to the pivot
how can you find the moment when a force is not perpendicular to the pivot
you can either resolve the force to find the perpendicular component to the distance
or finding the closest perpendicular distance to the pivot by resolving the distance
what is a couple in moments
a pair of equal forces acting in opposite directions, when a couple acts on an object, the object rotates in position
the moment of a couple is called the torque
what assumption do we make when we calculate moments
all the mass is concentrated in a single point on an object
what are the two conditions necessary for a system to be in equillibrium
the resultant forces on an object must be 0
the resultant moment on an object must be 0
how can you find the force from 2 pivots on a balanced object with an unevenly distributed iweight
neglect one of the pivots and find the moment due to the weight. Then, since the C and AC moments must equal, you can find the force due to the pivot. because the force on the object must be equal you can findthe force on the other pivot
What is the principle of moments
when a body is balanced the total clockwise moments will equal the total anticlockwise moment
howcan you find the moment from a force at an angle
resolve the force to get the perpendicular force to the distance from the pivot
what must happen before you can find the moment due to a force
the force and the distance must be perpendicular to eachother
you can either resolve the force or resolve the distance
define drag
A frictional force opposing motion due to an object moving through a fluid, proportional to the square of the object’s speed; and proportional to the surface area of the object in the plane perpendicular to the direction of motion
define work done
The transfer of energy when an object is displaced in parallel to the direction of the force
E=Fs
state the equation for GPE
GPE=mgh
what is power
the rate at which energy is transferred
P=E/t
state the equation for KE
KE=1/2 x m x v^2
describe and explain the motion of a ball thrown up into the air in terms of energy transfer
assume no energy is lost to surroundings
as soon as it is thrown, the valocity is the greatest because the KE is the greatest and the GPE is smallest
as it moves up, it slows down and the KE is converted into GPE
at the very top, the ball has a velocity of 0 since the KE is 0 and the GPE is at its highest
as it moves back down it accelerates as the KE increases and the GPE decreases
why does mass not affect the velocity of an object as it falls
rearrange the equations for KE and GPE to get mgh=0.5mv^2
cancel out m on both sides 2gh=v^2
hence the velocity of a falling object is not affected by the mass, only the height it falls from and the gfs
state the principle of conservation of energy
energy cannot be created or destroyed, only transferred
what is a system
a collection of components that all have the same total energy
no energy can leave or enter a system
rearrange equations for energy to find an equation for power in terms of velocity
E=Pt and E=Fs
so Pt=Fs
hence P=Fs/t
s/t = v
so P=Fv
define KE
Kinetic energy is the energy that an object possesses due to its motion.
define GPE
Gravitational potential energy is the energy stored in an object as a result of its vertical position within a gravitational field.
what is energy efficiency and how to calculate it
measure of how effective a device is at converting the energy supplied to it into useful energy
(useful output energy/total input energy) × 100
why is a 100% efficient device impossible
because some energy will always be converted into heat
this is the second law of thermodynamics
why are high efficiency devices important
because energy can be expensive and a higher efficiency is more cost effective
energy is still majorly sourced from non renewable sources of energy, so the less energy systems require to fully function, the more resources are conserved
define internal energy
the sum of the potential and kinetic energies of atoms in a system
what is the centre of mass
The centre of mass is the point through which any externally applied force produces straight line motion but no rotation
Write the definition of: Work-Energy Principle
The total work done by all the forces acting on a body is equal to the change in kinetic energy of the body
define gpe
The stored potential energy of an object due to position in a gravitational field, associated with the weight of a body at a given vertical height above the Earth’s surface, EP = mgh
define KE
The energy of a body due to the motion of the body, KE = 1/2 mv2
