Motion Flashcards
what is instantaneous speed
it is the speed of the car over a very short interval of time.
How do you calculate instantaneous speed
drawing a tangent to the graph and calculate the gradient of the tangent
What does this graph imply
A) stationary object
B) constant + speed
C) constant - speed
D) changing speed, slow to fast
E) changing speed, fast to slow
F) constant speed
what is the gradient of a distance-time graph?
∆d / ∆t = speed
what do displacement-time graphs represent
the gradient represents the velocity of an object.
what is the definition of velocity
it is the rate of change of displacement per unit time
What is the definition of speed
it is the rate of change of distance per unit time
what is the formula and units for acceleration
a = ∆v / ∆t units: ms-2
What is the gradient of a velocity-time graph?
∆v / ∆t = a
what do these velocity-time graphs represent
What does the AREA of a velocity-time graph represent?
ms-1 x s = m
from v x t = s
define stopping distance
it is the total distance travelled from when the driver first sees a reason to stop, to when the vehicle stops
what are the two components of stopping distance
thinking distance + braking distance = stopping distance
define thinking distance
the distance travelled between the moment when you first see a reason to stop, to the moment when you use the brake.
define braking distance
the distance travelled from the time the brake is applied until the vehicle stops
what is the formula for thinking distance?
thinking distance = speed x reaction time
when is an object said to be in free fall?
when an object is accelerating under gravity, with no other force acting on it
what is implied when an object is thrown
- the vertical velocity changes due to gravity
- horizontal velocity remains constant
why does the horizontal velocity of the projectile remain constant
the acceleration of free fall is vertically downwards, the component of this acceleration in the horizontal direction is 0
how can we calculate the actual velocity of a projectile
when an object is fired at an angle θ how can the motion be analysed
splitting the force into components
vx= v(cos(θ))
vy= v(sin(θ))
how can we use an electromagnet and trapdoor to calculate g
- an electromagnet holds a small steel ball above a trapdoor
- when current is switched off, a timer is triggered,
- the ball falls
- when it hits the trapdoor, the electrical contact is broken and the timer stops.
- calculate g from height and time taken
example of electromagnet and trapdoor practical
how can we use Light Gates to calculate g
- two light beams, one above the other, with detectors connected to a timer
- when the ball falls through the first beam, it interrupts light and timer starts
- when the ball falls through the second a known distance the timer stops
how can we use pictures to calculate g
- a steel ball is dropped from test next to a metre rule, its fall is recorded on video
- the position of the ball at regular intervals is then determined by examine the recording
example of using pictures to calculate g
define weight
the gravitational force acting on an object through its centre of mass
define drag
frictional force that opposes the motion of the object in fluid
- speed ∝ drag2
- increased cross sectional area increases drag
define upthrust
an upward buoyancy force acting on an object when it is in a liquid
representing an object on a slope
terminal velocity
when the drag force on an object is equal and opposite to the weight of the object, there is no resultant force and therefore the speed remains constant
define moment
the moment of a force is the turning effect of a force about some axis or point
- moment = force x perpendicular distance of the line of action of the force or point of rotation
- moment = Fx
principle of moments
for a body in rotational equilibrium, the sum of the anticlockwise moments is equal to the sum of clockwise moments about the same point
define couple
two forces must be parallel and along different lines in the opposite direction
define torque
the moment of a couple is known as a toque it is defined as
- torque of a couple = one of the forces x perpendicular separation between the forces = Fd
define pressure
the normal force exerted per unit cross-sectional area
- p = F/A
- calculate pressure in liquids
- p(ressure) = hpg
- h - height of the liquid column
- p - density
- g - gravity
archimedes principle
the upthrust exerted on a body immersed in a fluid whether fully or partially submerged is equal to the weight of the fluid that the body displaces
upthrust formula
upthrust = Axpg
A - area
x - depth
p - density
g - gravity
what is work done
work done = force x distance moved in the direction of the force
W = Fx
principle of conservation of energy
the total energy of a closed system remains constant: energy can never be created or destroyed, but it can be transferred from one form to another
energy exchange
Ek = ½mv2
GPE Ep = mgh
mgh = ½mv2
gh = ½v2
define power
power is the rate of work done
p = w/t
p- power
w - work done
t - time
power and motion
- a constant force F moves the car a distance x in a time t
- work done by the force W = Fx
- P= w/t = Fx/t
- (x/t) = velocity
- P = Fv
efficiency formula
efficiency = ( useful output energy / total output energy ) x 100
tensile and compressive forces
- forces that produce extension are known as tensile forces
- forces that shorten an object are known as compressive forces
- a helical spring undergoes tensile deformation when tensile forces are exerted
- similarly compressive deformation occurs when compressive forces are exerted
hookes law
- the extension of the spring is directly proportional to the force applied as long as the elastic limit of the spring is not exceeded
- F = kx
- k - force constant which is a measure of the stiffness of a spring
describe the force extension graph
- straight line from the origina up to the elastic limit (A)
- in this region it undergoes elastic deformation, will therefore return to its original length when the force is removed
- beyond A is plastic deformation: permanent structural changes to the spring occur and doesnt return to its original state
- area under graph = work done
elastic potential energy
E = ½Fx = ½(kx) * x
F - force producing an extension x
E = ½kx2
tensile stress
- defined as the force applied per unit cross-sectional area of the wire
- tensile stress = force/cross-sectional area
- σ = F/A
tensile strain
defined as the fractional change in the original length of the wire
tensile strain = extension/original length
Ɛ = x/L
- stress ∝ strain from the origin to P, the limit of proportionality
- E represents the elastic limit
- elastic deformation occurs up to the elastic limit and plastic deformation beyond that
- y1 and y2 are upper and lower yield points ,where material extends rapidly
- UTS , ultimate tensile strength is the maximum stress that a material can withstand when being stretched before it breaks
young modulus
the ratio of stress to strain for a particular material is a constant and is known as its young modulus, E.
young modulus = tensile stress/ tensile strain
E = σ / Ɛ
newtons first law
an object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force.
newtons third law of motion
when two objects interact, they exert equal and opposite forces on each other
momentum
product of mass and velocity
p = mv
principle of conservation of momentum
for a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system
what is the difference between perfectly elastic and inelastic collisions
newtons second law
the net force acting on an object is directly proportional to the rate of change of its momentum and is in the same direction
F = P/t
F is the net force, P is the change in momentum over time interval t
F = ma for momentum
- F = ma
- a = (v-u)/t
- F = m(v-u)/t
- F = (mv-mu)/t
- F = p/t
