PHYA2 - Speed and Velocity 0.0 / 5 ? PhysicsMotionASAQA Created by: FranklinCreated on: 11-05-14 14:53 Speed and velocity Speed: the change in distance per unit time Velocity: the change in displacement per unit time Displacement: distance in a given direction Motion at constant speed Speed v = s/t circle speed v=2 r/T where T is the time take to move round once Speed = gradient of a distance-time graph Velocity = gradient of displacement-time graph 1 of 9 Distance-time graph with variable speed 2 of 9 Displacement-time graph Gradient of displacement-time graph = velocity, however acceleration is indicated by the curve 3 of 9 Acceleration Acceleration: the change in velocity per unit time Acceleration is a vector quantity, deceleration is negative 4 of 9 SUVAT Equations 5 of 9 Motion Graphs The case of a ball thrown upwards is used below The ball reaches a maximum height (when velocity is instantaneously zero) then descends Intially the gradient is positive and large because as the ball leaves the hand the velocity is high As the ball rises the velocity decreases because it is acting against gravity As the ball descends the velocity increases due to gravity Difference between distance-time and displacement time graphs Displacement-time graph 6 of 9 Motion Graphs (cont.) Distance-time graph 7 of 9 Velocity-time and speed-time graphs The case of a ball thrown upwards is used below The ball reaches a maximum height (when velocity is instantaneously zero) then descends Intially the gradient is positive and large because as the ball leaves the hand the velocity is high As the ball rises the velocity decreases because it is acting against gravity As the ball descends the velocity increases due to gravity Velocity-time graphs Gradient represents acceleration Area beneath a velocity-time graph is displacement The positive area represents displacement during ascent since upwards is considered positive The negative area represents displacement during descent since downward is considered negative 8 of 9 Velocity-time graph for ball 9 of 9

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