P9 Motion Flashcards
Distance and displacement
Distance is a measure of how far an object travels
-it is a scalar quantity
Displacement is a measure of how far something is from its starting position,a long with its direction
-it is a vector quantity-both magnitude and direction
Consider a 300m rave
-the athletes would run a distance of 300m however their displacement at the end of the rave is 100m to the right
-if they had ran a full 400m, their final displacement would be 0
Speed and non-uniform motion
Speed of an object is the distance it travels every second
-it is a scalar qauntity
Average speed= total distance/time taken
Distance= metres
Time=seconds
Speed=m/s
Non-uniform motion refers to motion thag is changing
Changing motion can mean the object is changing speed,direction or both
Calculating speed and
Speed=distance travelled/time taken
V=S/T
V=speed in metres per second
S=distance travelled in metres
T=time taken in seconds
Velocity
The velocity of a moving object is similar to its speed,except it also describes the object’s direction
Velocity is a vector quantity as it has both direction and magnitude
Vector and scalar quantities-distance,displacement,speed,velocity
Distance:
Type:scalar
Definition:how far an object travels
Displacement:
Type:vector
Definition: the distance lf an object from its starting position,along with its direction
Speed:
Type:scalar
Definition: the distance an object travels every second
Velocity:
Type:scalar
Definition:the speed of a moving object and its direction
Circular motion
-velocity is a vector quantity
-when an object travels in a circular path, its velocity is always changing
The speed of the object moving in a circle might be constant-that is, it is travelling the same distance every second
However, the direction of travels is always changing as the object moves in a circular path
A change in velocity is defined as acceleration, so although the object isn’t speeding up, it is accelerating due to the changing direction
Displacement-time graphs
-a straight line represents constant speed
-a steeper slope means the object is moving at a large speed
-a shallow slope means the object is moving at a small speed
-a flat horizontal line means object is stationary
-gradient is velocity
-objects might be moving at changing speed-represented by a curve
-if slope is increasing the object is accelerating
-if slope is decreasing the object is decelerating
-if an object is accelerating, its speed can be determined by drawing a tangent and calculating the gradient of the distance-time graph
Instantaneous soeed
-if an object speed is changing, then distance-time graph will be a curve
-if it accelerating, then line curve will be upwards
-if decelerating line curve will be downwards
Speed=gradient= rise/run
Acceleration
Acceleration is defined as the rate of change in velocity
-describes how much a objects velocity changes every second
Acceleration= change in velocity/time taken
Acceleration= m/s squared
Velocity=m/s
Time= seconds
Chnages in velocity = final velocity-initial velocity
Speeding up and slowing down:
If object speeds up it is accelerating
If object slows down it is decelerating
-acceleration of an object can be positive or negative, depending wether object is speeding up or slowing down
If object is speeding up, its acceleration is positive
If object is slowing down, its acceleration is negative (deceleration)
Velocity-time graph
-gradient is acceleration
-sharper gradient means sharper acceleration
-negative gradient means deceleration
-horizontal line means constant speed
-0 velocity means stationary
Area under graph shows distance travelled of object
-if area beneath forms a triangle area=1/2 x base x height
-if an object with changing acceleration, its velocity-time graph will be a curve so estimate the distance travelled by counting the squares underneath curve
Uniform acceleration
(Final speed)2= (initial speed)2 +2(acceleration)(distance)
Terminal velocity
When a skydiver jumps out a plane, two forces act on it:
-weight (due to gravity =9.8 m/s)
-air resistance (due to friction)
-the resultant force of a skydiver decreases as they fall
-initially, the upwards resistance is very small because the skydiver isn’t falling very quickly
-as they speed up, the air resistance increases, eventually growing large enough to balance the downwards weight force
-once air resistance equals weight, there is no longer any resultant force
-therefore divers acceleration is 0-travelling at constant speed
-this is called terminal velocity
Graphs of motion
Distance-time graphs:
Distance: read values from graph
Velocity= gradient
V=D/T (use a tangent)
Velocity-time graphs:
Distance: area under graph
Velocity: read values from graph
Acceleration: the gradient
A= change in velocity/ time (use a tangent)
