2.motion graphs of physics igcse 0625 notes

IGCSE 0625 Physics , Revision Notes

1. MOTION GRAPHS The motion of the objects can be shown with the help of distance - time and speed – time graphs. Distance – time graphs Object at rest (stationary object)

2. Object moving with constant speed Object increasing speed non - uniformly (accelerating)

3. Object decreasing speed constantly Object decreasing speed non - uniformly (decelerating non - uniformly)

4. Note: The gradient of the distance-time graph represents the speed of the object.

5. Example Question: The graph shown below represents the distance traveled by a car plotted against time.

6. (a) Describe the motion of the car between point A and E. Between A and B the speed of the car increasing, then between B and C car moves with constant speed, after that between C and D the speed of the car decreasing and between D and E car is at rest. (b) How far has the car travelled at the end of 30seconds ? 60 m ( c) Calculate the speed of the car between point B and C ? ( e) What is the distance travelled between A and D ? ( f)What is the average speed between A and D?

7. Speed – time graphs Object at rest (stationary object) Object moving with constant speed

8. Object moving with uniform acceleration Object moving with non - uniformly acceleration

9. Object decelerating uniformly Object decelerating non - uniformly

10. Note : the gradient of the speed-time graph is equal to the acceleration of the object.

11. Speed The Area Under Speed-Time graph represent the Distance. Area=1/2( t×v ) Area= t×v A=1/2(s) Area=s=distance

12. Example question: The speed – time graph below shows the motion of a car. (a) Describe the motion of the car.

13. (b) Calculate the acceleration of the car between 2s and 4s. (c) Calculate distance travelled by the car between 5s and 7s.

14. Free fall When an object is released near to the surface of the Earth, it falls under the influence of gravity. This is known as free fall. The acceleration of free fall or acceleration due to gravity is denoted by g . The acceleration due to gravity is 9.8m/s 2 . This is true in the absence of air resistance . The experiment below shows, all the air has been removed from the tube. Both feather and lead ball dropped from same height and reaches bottom of the tube at the same time. This is because all the objects in the absence of air resistance, accelerates towards the earth at same rate that is10m/s 2 .

15. terminal velocity Falling objects accelerate due to the pull of Earth’s gravity. However, a falling object stops accelerating when it reaches terminal velocity. At this point, the downward force of its weight is balanced by the upward force of air resistance . Terminal velocity is the constant velocity of a falling object reaches when the vertical forces acting on it are balanced . when Weight = Air Resistance

16. 30 September 2024 Consider a parachutist jumping from aircraft . When the parachutist jumps from the aircraft, his speed increase downward due to weight of his body or gravitational force As his speed increases his air resistance will also increases in the opposite direction of fall. After sometime air resistance will be big enough to balance the parachutist’s weight. At this point the forces are balanced so his speed becomes uniform - this is called terminal velocity .

17. 30 September 2024 When he opens his parachute the air resistance suddenly increases and the speed decreases. After some time again air resistance decreases until it balances his weight. The parachutist has now reached a new, lower terminal velocity . Air Resistance Weight

18. 30 September 2024 speed Time Speed increases… Terminal velocity reached… Parachute opens – diver slows down New, lower terminal velocity reached Diver hits the ground Speed-time graph of a parachutist is shown below … Speed decreasing