SpeedTime Graphs Interpreting Velocitytime graphs the gradient of

Interpreting Velocity/time graphs • the gradient of a velocity/t graph is the acceleration v

Interpreting Velocity/time graphs Faster constant acceleration v Slow constant acceleration t Constant acceleration (the

Interpreting Velocity/time graphs decreasing acceleration v Increasing acceleration t Changing acceleration (the rate of

Interpreting Velocity/time graphs RC Car Journey B v C D A t • •

Acceleration • An object changing its speed is said to be accelerating. If the

Acceleration (change in speed) • acceleration is a measure of how quickly the velocity

Example • A racing car speeds up from 8 ms-1 to 24 ms-1 and

Examples 1. A cyclist starts from rest and accelerates to 15 ms-1 in 8

Calculating the Gradient (v/t graphs) • the gradient of a velocity/time graph is the

Velocity/time graphs • The area under the graph is the distance travelled (as the

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Speed-Time Graphs

Interpreting Velocity/time graphs • the gradient of a velocity/t graph is the acceleration v t Constant velocity (the velocity remains the same)

Interpreting Velocity/time graphs Faster constant acceleration v Slow constant acceleration t Constant acceleration (the velocity changes at a constant rate)

Interpreting Velocity/time graphs decreasing acceleration v Increasing acceleration t Changing acceleration (the rate of change in velocity per second changes)

Interpreting Velocity/time graphs RC Car Journey B v C D A t • • A -fast acceleration (steep gradient and line straight) B –slower acceleration (shallow gradient and line straight) C –constant velocity (line horizontal) D –Very fast deceleration (steep gradient, straight line, sloping down)

Acceleration • An object changing its speed is said to be accelerating. If the acceleration is: – positive (eg. 2 ms-2) = object speeding up – negative (eg. -2 ms-2) = object slowing down or decelerating

Acceleration (change in speed) • acceleration is a measure of how quickly the velocity (speed) of an object is changing • If the object is a constant acceleration (unbalanced forces) the formula is; Note; v =final velocity-initial velocity v=vf - vi • The units for acceleration are ms-2

Example • A racing car speeds up from 8 ms-1 to 24 ms-1 and takes 8 s to do so. Calculate the acceleration. = 24 – 8 = 16 ms-1 A = 16 ms-1 8 s = 2 ms-2

Examples 1. A cyclist starts from rest and accelerates to 15 ms-1 in 8 s. Calculate her acceleration 1. 9 ms-2 2. A runner jogging at 2. 5 ms-1 increases his pace to 4. 5 ms-1 in 3 s. What was her acceleration? 0. 7 ms-2

Calculating the Gradient (v/t graphs) • the gradient of a velocity/time graph is the acceleration Velocity Gradients 30 Velocity (m/s) 25 20 15 10 5 0 0 2 4 6 8 10 12 14 Time (s) For the blue line; For the green line; For the red line; Gradient=Rise/Run =6/12 =(14 -2)/12 =24/12 =0. 5 ms-2 =1. 0 ms-2 =2. 0 ms-2

Velocity/time graphs • The area under the graph is the distance travelled (as the cut up ticker timer tape showed) Car Journey 10 9 Velocity (m/s) 8 7 6 5 4 3 2 1 0 0 2 4 6 8 10 12 Time (s) Area of triangle=½base ×height Area of rectangle=base × height = ½× 6× 9 = 4× 9 =27 m =36 m Total area=27+36=63 m

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