Topic 8 - Kinematics Flashcards
scalar quantity
a quantity with magnitude but no direction
vector quantity
a quantity with magnitude AND direction
distance
- scalar quantity
- how far an object has moved
displacement
- vector quantity
- distance and direction in a straight line from starting point to finishing point of an object ( with bearing )
speed
- scalar quantity
- how fast an object is moving with no regard to direction
velocity
- vector quantity
- how fast an object is moving and in which direction ( bearing )
speed equation
speed = distance / time
moving in a circle
- constant speed while the velocity is constantly changing as…
- velocity is a vector with both magnitude and direction
- constantly changing direction
walking typical speed
1.5 m/s
running and cycling typical speed
running : double walking
cycling : double running
acceleration equation
change in velocity / time
v - u / t
distance - time graphs
- gradient = speed
- straight uphill sections = steady speed
- straight line = stationary
- steep curved section = accelerating
- leveling curve = decelerating
velocity - time graphs
- gradient = acceleration
- straight line = constant speed
- steeper = greater ac/deceleration
what is a resultant force?
the resultant force has the same effect as all the individual force acting on the object in a straight line
what is a force
- a vector quantity
- a push or pull that acts on an object due to an interaction with another object
contact forces acting on a body
- forwards thrust
- driving force
- friction
- air resistance (opposite direction)
- normal contact force from the ground acts upwards
non contact forces
- weight caused by gravitational force acts downwards
- electrostatic force
- magnetic force
Newton’s First Law
if the r.f on an object is zero then it will continue moving at the same velocity
- if it is stationary it will remain stationary
Newton’s Second Law
- an object’s acceleration is directly proportional to its resultant force
F = ma
inertia
an object’s tendency to continue moving at same velocity
inertial mass
how difficult it is to change velocity of an object
F/ a
Newton’s Third Law
- when two objects interact, the forces they exert on each other are equal and opposite
what is friction? how is it affected by speed
frictional forces act in the opposite direction of movement
- as speed of an object increases the frictional forces also increase
what are most of the resistive forces caused by?
air resistance or drag
how does a falling object reach terminal velocity?
- when a falling object first sets off,
- the force of gravity is much greater than the frictional air resistance pushing upwards.
- object accelerates downwards
how does a falling object reach terminal velocity? (P2)
- with increasing speed, the air resistance also increases, reducing acceleration
- eventually, the air resistance pushing upwards equals the force of gravity pushing downwards
- it will reach its terminal velocity, stay at same speed and stop accelerating
gravity
the force that makes objects with mass attract to each other
it makes all things accelerate towards the ground
weight
the force acting on an object due to gravity
weight equation
W= mg
work done
work done = force x distance
how does a moving object heat up?
- when an object moves it does work against friction
- some energy is transferred by heating to thermal energy stores of object
- and away from KE of object
- overall temp of object and surface increase
stopping distance
distance covered in the time between a driver spotting a hazard and the vehicle coming to complete stop
stopping distance equation
thinking distance + braking distance
thinking distance
distance the vehicle travels during the time between the driver seeing a hazard and applying the breaks
braking distance
distance the vehicle travels after braking force is applied
why do objects fall at a slower rate on the Moon than the earth?
- moon’s g.f.s is much lower
- the weight of object is much lower on moon than earth
- gravity causes objects to accelerate towards the ground : objects accelerate slower on moon
what factors affect the strength of gravitational field?
the closer you are to the centre of mass causing the gravitational field, the stronger it is
factors affecting thinking distance
- vehicle speed
- reaction time which is affected by drugs, alcohol or tiredness
factors affecting braking distance
- vehicle speed
- brake condition
- tyre condition
- road condition
how does speed affect thinking distance
- thinking distance is directly proportional to speed
how does speed affect braking distance
- braking distance increases by a scale factor of speed increase
- 1/2mv2
car safety : seatbelts
- stretches slightly and prevents component from exiting vehicle in crash
car safety : air bags
increase collision time for head and chest
3 SUVAT equations
v2 = u2 + 2as
v = u + at
s = ut + 1/2 at
