UNIT-1 Motion-Speed-time and distance - time graph.pptx

Interpreting and plotting Speed - time and distance - time graph

1. MOTION SPEED-TIME GRAPH

2. Plot and interpret a speed–time graph Recognise from the shape of a speed–time graph when a body is – at rest – moving with constant speed – moving with changing speed Calculate acceleration from the gradient of a speed–time graph Calculate the area under a speed–time graph to work out the distance travelled for motion with constant acceleration OUTCOME

3. Recognise linear motion for which the acceleration is constant Recognise motion for which the acceleration is not constant Understand deceleration as a negative acceleration Demonstrate understanding that acceleration and deceleration are related to changing speed including qualitative analysis of the gradient of a speed–time graph State that the acceleration of free fall for a body near to the Earth is constant OUTCOME

4. Straight horizontal line along x-axis Stationary body Speed = 0 Object moving at rest

5. Straight horizontal line Acceleration = zero Object moving with constant speed

6. Linear motion is motion across a straight line. Acceleration on a speed-time graph is constant when the line is straight. Straight line passing through origin Object moving at a constant acceleration

7. Line curving downwards indicating decreasing acceleration (A) Line curving upwards indicating increasing acceleration (B) Object moving at a varying speed A B If on the speed-time graph the line is bent or curved it does not have a constant acceleration, because the gradient of the line changes.

8. Speed – time graph

9. Graph of speed of a body against time. Speed plotted along Y axis Time plotted along X axis Gradient of speed-time graph = acce l eration m = a Speed-time (v-t) graph Acceleration, a =  

10. Speed – time graph With this graph we can tell three things; the speed ; directly off of the graph. the acceleration ; by calculating the gradient of the line. the distance it has travelled; by calculating the area under the graph.

11. Speed – time graph Speed = 16 m/s

12. Gradient, m Gradient is a unit less quantity Gradient, m = = = 170 – 10 / 32 – 4 = 5 . 7  

13. Ca l cu l ating Gradient, m Gradient of speed-time graph = acceleration m = a = = 40 – 10 / 4 – 1 = 10 m/s 2   m =   m = = 40 – 10 / 4 – 1 m = 10 a = 10 m/s 2   m = a

14. Distance trave ll ed fr o m Speed – time graph Area under speed-time graph = distance trave ll ed (s) s = A = ( ½ × b × h ) + ( l × b ) + ( ½ × b × h ) = ( ½ × 10 × 16 ) + ( 10 × 16 ) + ( ½ × 5 × 16 ) = 80 + 160 + 40 = 280 m A B C

15. Speed – time graph Area under speed-time graph = distance trave ll ed s) s = Area o f trapezium = ½ × ( base1 + base2 ) × h = ½ × ( 10 + 25 ) × 16 = 280 m A B C base1 base2

16. Demonstrate a qualitative understanding that acceleration is related to changing speed.   Acceleration is the rate of which an object changes speed, so when a speed changes, we assume that the acceleration has either increased or decreased.  Acceleration, a =   Deceleration refers to acceleration in the direction opposite to the direction of the velocity

17. State that the acceleration of free fall for a body near to the Earth is constant Acceleration is the rate of which an object changes speed, so when a speed changes, we assume that the acceleration has either increased or decreased.