P11 Speed Flashcards
distance vs displacement
distance is how far an object moves and is a scalar quantity (no direction)
displacement is a vector and includes distance and direction of a straight line from start point to finish point
speed
(average) speed = distance / time
v = s / t
typical average speeds (waking, running, cycling, sound)
1.5
3
6
300 m/s
velocity
speed in a given direction - vector quantity
so:
changes if direction changes, even if speed stays constant
if an object moves in a circle it can have constant speed but velocity will always be changing
acceleration
change in velocity per second - vector quantity
m/s2
change in velocity / time
negative acceleration is called deceleration (but is still counts as acceleration)
uniform acceleration (+ eq that applies to objects with this)
when acceleration of an object is constant
v2 - u2 = 2as
drag forces
frictional forces that action on objects moving through fluids (liquids or gases):
- always act in opposite direction to object’s movement
- increase with object’s speed - the greater the speed, the greater the frictional force
- depends on the shape and size of the object
called air resistance when in air
how to reduce drag forces on an object
streamline it
distance-time graphs
velocity-time graphs
terminal velocity
constant velocity a falling object reaches when the frictional force acting on it is equal to its weight
for an object falling through a fluid: (text)
- 2 forces - weight due to gravity, and drag force
- weight remains constant
- drag force starts small but increases with speed
- as drag force increases resultant force gets smaller - acceleration decreasing
- there will reach a point when frictional drag force = weight - object will reach a final steady speed
for an object falling through a fluid: graph
