Physics - Mechanics Flashcards
what type of quantity is speed
scalar quantity
speed equation
speed = d / t
what type of quantity is velocity
vector quantity
velocity equation
velocity = displacement / time
what type of quantity is acceleration
vector
acceleration equation
acceleration = velocity / time
what is acceleration
rate of change of velocity
what is acceleration
rate of change of velocity
distance time graph -
what does straight line mean
stationary object
distance time graph -
what does a straight diagonal line mean
object moving with constant velocity
distance time graph -
what is the gradient of the line
the velocity
distance time graph -
what is on x and y axis
x = time
y = distance
distance time graph -
what is a curved line
accelerating object
velocity time graphs -
what is does a horizontal line mean
object moving w constant velocity
velocity time graphs -
what does a straight diagonal line mean
constant acceleration
velocity time graphs -
what is the gradient of the line
acceleration
velocity time graphs -
what is the area under the graph
displacement / distance travelled
equation involving
- final velocity
- initial velocity
- acceleration
- time
v = u + at
equation involving
- displacement
- initial velocity
- final velocity
- time
s = 0.5(u+v)t
equation involving
- final velocity
- initial velocity
- acceleration
- displacement
v^2 = u^2 +2as
what is a force
interaction between two or more objects
how is acceleration caused
unopposed force
what type of quantity is force
vector
what is the unit for force
Newtons (N)
resultant force
sum of all forces
what is tension force
when a spring/string/wire is pulled by equal and opposite external forces at each end and as shown, said to be subjected to a tension force
tension force typically causes extension on length of spring/string
greater the tension, greater the extension
force-extension characteristics on a graph - what does it mean if the graph is steeper
more force required to produce a given extension
force-extension characteristics on a graph -
what does it mean if the graph is shallower
greater the extension for a given force
when is a material described as rigid
if its deformation is small even with a large tension force
force-extension characteristics of copper wire
stretches uniformly initially, until it suddenly stretched more just before reaching breaking point
force-extension characteristics of glass
very rigid
deforms only very slightly before breaking
force-extension characteristics of rubber
stretches non-uniformly
what does elastic mean
means the material will return to its original lenth when tension is removed
what does inelastic mean
material does not return to its original length when the tension is removed
PLASTIC DEFORMATION
plastic deformation
material does not return to its original length when the tension is removed
what is the elastic limit
point at which extension goes from elastic to inelastic
what is Hooke’s Law
extension is proportional to force applied
F = Kx
F = force in N
x = extension in metres
K = spring constant in N/m
what is spring constant a measure of
rigidity
higher spring constant means higher force is required to produce a certain extension
limit of proportionality
point on force extension graph where the line is no longer straight
material no longer obeys Hooke’s Law (elastic limit)
what is spring constant affected by
- cross sectional area of spring (increased cross sectional area of spring increases spring constant)
- length of spring (longer the spring, smaller the spring constant)
two identical springs in series will have resultant spring constant of ..
0.5 x spring constant of 1 spring
two identical springs in parallel will have resultant spring constant of ..
2 x spring constant of 1 spring
what happens when a spring is stretched
work is done
energy is stored as elastic potential energy in the spring
if elastic limit is not exceeded, energy will be released as kinetic energy
area under a force extension graph equation
E = 0.5Fx
E = 0.5Kx^2
what happens if material is stretched beyond elastic limit
work done is partially or completely irretrievable as material will no longer return to its original length
newtons first law
an object will remain stationary or moving at a constant velocity unless a force acts upon it
if resultant force is zero, then objects will also remain stationary or moving at a constant speed
when a resultant force acts upon an object, the object will accelerate in the direction of the force
newtons second law
acceleration of an object is directly proportional to the resultant force acting upon the object
furthermore, acceleration of an object is inversely proportional to the mass of an object
resultant force = mass x acceleration
F=ma
newtons third law
force exerted by object A on object B is equal in magnitude and opposite in direction to the force exerted by object B on object A
what is momentum
quantity of motion of moving body that is a product of its mass and velocity
has symbol italic p
measured in Kgm/s
momentum in a closed system
conserved
force applied to change momentum equation
force = change in momentum / change in time
car safety features
seatbelts and crumple zones
extends time over which momentum changes, force exerted on passengers reduced
occurs by using relationships between force, momentum and time
mass
quantity of object
regardless of volume or forces
symbol M
measured in kg
weight
force exerted on body by gravity
symbol W
measured in N
how is weight calculated
mass of object x g
g = 10 !!!!!!!
what happens when an object is in free fall
two forces acting on object is weight downwards and aerodynamic drag acting in opposite direction
object starts falling , weight acting down > aerodynamic drag , therefore has acceleration down
as object accelerates, magnitude of aerodynamic drag increases
drag increases until it is equal to objects weight, at this point there is no resultant force acting on the object so it moves at constant velocity (TERMINAL VELOCITY)
terminal velocity
drag increases until it is equal to objects weight, at this point there is no resultant force acting on the object so it moves at constant velocity
why do skydivers use a parachute
increase their aerodynamic drag causing them to decelerate until the forces are once again balanced, and they continue to fall at a new, lower terminal velocity
energy
capacity of a body to do wok and work done is analogous to energy transferred
measured in J
work done equation
work done = force x distance
power
rate of energy transfer
power equation
power = energy / time
GPE
energy stored in an object due to position in a gravitational field
change in GPE equation
mass x acceleration due to gravity x change in height
kinetic energy equation
1/2 x mass x velocity^2
what happens when there is no drag/resistance
all GPE will be converted to kinetic energy so
M x G x H = 1/2 x M x V^2
what are the 9 forms of energy
- heat
- light
- sound
- kinetic
- electric
- nuclear
- elastic potential
- gravitational potential
- chemical potential
